oversight

Nuclear Regulatory Commission: Natural Hazard Assessments Could Be More Risk-Informed

Published by the Government Accountability Office on 2012-04-26.

Below is a raw (and likely hideous) rendition of the original report. (PDF)

             United States Government Accountability Office

GAO          Report to Congressional Requesters




April 2012
             NUCLEAR
             REGULATORY
             COMMISSION
             Natural Hazard
             Assessments Could Be
             More Risk-Informed




GAO-12-465
                                           April 2012

                                           NUCLEAR REGULATORY COMMISSION
                                           Natural Hazard Assessments Could Be More Risk-
                                           Informed
Highlights of GAO-12-465, a report to
congressional requesters




Why GAO Did This Study                     What GAO Found
On March 11, 2011, an earthquake           The Nuclear Regulatory Commission (NRC) and companies licensed to operate
triggered a tsunami wave that              nuclear power reactors (or licensees) apply probabilistic risk assessment (PRA)
exceeded the seawall at Japan’s            to natural hazards at operating U.S. nuclear reactors to a limited extent. When
Fukushima Daiichi nuclear power            the 104 operating reactors were originally licensed before 1997, NRC required
plant, leading to the release of           licensees to assess natural hazards using deterministic analysis, which—
radioactive material into the              informed by historical experience, test results, and expert judgment—considers a
environment. The disaster raised           specific set of potential accidents and how the consequences of those accidents
questions about the threats that natural   can be prevented and mitigated. Subsequent to most of these initial licenses
hazards, such as earthquakes and
                                           being issued, NRC, through policy statements and other documents, has
floods, may pose to U.S. commercial
                                           endorsed PRA—a systematic method for assessing what can go wrong, its
nuclear power reactors. NRC licenses
and regulates U.S. nuclear power
                                           likelihood, and its consequences, resulting in quantitative estimates of risk—as a
reactors. NRC criteria for licensees to    means to enhance and extend traditional deterministic analysis. In 1991, NRC
assess natural hazards were                requested that licensees voluntarily examine their reactors’ vulnerability to
developed using an approach that           natural hazards and suggested PRA as one of several possible methods for
required reactors to be designed           licensees to use in their examinations. However, most licensees opted to use
according to a set of potential            other methods. According to NRC officials and nuclear power industry
accidents using deterministic analysis.    representatives—and reflected in data GAO obtained from five licensees that
Since the 1990s, NRC has been              together operate 25 reactors—few licensees are likely to have developed or
encouraging the use of PRA as part of      updated since the 1990s PRAs that address natural hazards. NRC would have to
a risk-informed, performance-based         conduct an analysis to determine whether or not to require licensees to develop
approach.                                  PRAs that address natural hazards. According to agency officials, NRC has not
GAO was asked to (1) determine the         conducted such an analysis.
extent to which PRA is applied to          The experts in assessing natural hazards and/or nuclear reactor risks that GAO
natural hazards at operating U.S.          interviewed offered a range of views on (1) the overall adequacy of NRC
reactors and (2) describe expert views     processes for assessing the threats that natural hazards pose to operating U.S.
on and suggested changes, if any, to       nuclear power reactors and (2) what, if any, changes to those processes are
NRC processes for assessing natural        warranted. Several experts said they believe NRC processes are generally
hazards at such reactors. GAO
                                           adequate for assessing the threats that natural hazards pose to operating
reviewed documents; analyzed
                                           reactors. However, more than half of the experts GAO interviewed suggested
responses from 15 experts in
assessing nuclear reactor risks and/or     expanding the use of PRA for assessing natural hazards as a complement to
natural hazards; visited five selected     traditional deterministic analyses to provide a more robust approach. Those
nuclear power plants; and interviewed      experts cited a number of advantages to doing so, including that PRA can help
NRC officials and industry and public      identify vulnerabilities that might otherwise be overlooked by relying on traditional
interest group representatives.            deterministic analyses alone. Several experts also identified challenges to
                                           expanding the use of PRA for assessing natural hazards, including the limited
What GAO Recommends                        number of experts qualified to develop PRAs and the costs of doing so.
GAO recommends that NRC analyze
whether licensees of operating
reactors should be required to develop
PRAs that address natural hazards.
NRC agreed with the recommendation
and stated it will conduct the analysis
in the context of ongoing initiatives.

View GAO-12-465. For more information,
contact Frank Rusco at (202) 512-3841 or
ruscof@gao.gov.

                                                                                    United States Government Accountability Office
Contents


Letter                                                                                    1
               Background                                                                6
               PRA Is Applied to Natural Hazards to a Limited Extent                    15
               Experts Offered a Range of Views on NRC Assessment Processes             22
               Conclusions                                                              28
               Recommendation for Executive Action                                      29
               Agency Comments and Our Evaluation                                       29

Appendix I     Objectives, Scope, and Methodology                                       31



Appendix II    List of Experts                                                          34



Appendix III   Key Developments in NRC’s Approach to Probabilistic Risk
               Assessment                                                               35



Appendix IV    Information on Developing a Probabilistic Risk Assessment                41



Appendix V     NRC Actions on Natural Hazard Assessment in Response to the
               Fukushima Daiichi Disaster                                               43



Appendix VI    Comments from the Nuclear Regulatory Commission                          47



Appendix VII   GAO Contact and Staff Acknowledgments                                    49



Tables
               Table 1: Natural Hazard PRAs at Selected Nuclear Power Reactors          18
               Table 2: Selected Techniques Used in PRA                                 42




               Page i                               GAO-12-465 Nuclear Regulatory Commission
Figure
         Figure 1: U.S. Operating Commercial Nuclear Power Reactors by
                  Power Plant Location                                                             7




         Abbreviations

         IPEEE             Individual Plant Examination of External Events
         NRC               Nuclear Regulatory Commission
         PRA               probabilistic risk assessment


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         Page ii                                        GAO-12-465 Nuclear Regulatory Commission
United States Government Accountability Office
Washington, DC 20548




                                   April 26, 2012

                                   The Honorable Barbara Boxer
                                   Chairman
                                   Committee on Environment and Public Works
                                   United States Senate

                                   The Honorable Edward J. Markey
                                   House of Representatives

                                   On March 11, 2011, a 9.0-magnitude earthquake and subsequent
                                   tsunami devastated northeast Japan and led to the most extensive
                                   release of radioactive material at a nuclear power plant since the 1986
                                   Chernobyl disaster. The Fukushima Daiichi nuclear power plant suffered
                                   extensive damage when a tsunami wave that exceeded the plant’s
                                   seawall flooded the site and caused a prolonged loss of electrical power
                                   at several of its reactors. As a result of the loss of power, plant operators
                                   were unable to keep three of the reactors cool, which led to fuel melting,
                                   hydrogen explosions, and the release of radioactive material into the
                                   environment. The disaster displaced tens of thousands of residents and
                                   contaminated the surrounding area. The Japanese government expects
                                   recovery to take years and cost billions of dollars. In light of the disaster,
                                   Japan and other countries have decided to reduce their reliance on
                                   nuclear power, which could affect their electricity costs and output of
                                   carbon emissions.

                                   In the United States, the Nuclear Regulatory Commission (NRC), an
                                   independent federal agency headed by five commissioners, licenses
                                   commercial nuclear power reactors and regulates and oversees their safe
                                   operation and security. 1 An NRC task force has reviewed the Fukushima
                                   Daiichi disaster and determined that the continued operation of existing
                                   U.S. nuclear power reactors and the licensing of new reactors do not
                                   pose an imminent risk to public health and safety. Nevertheless, the
                                   disaster and its origins in a natural hazard—a tsunami—that was more
                                   severe than the plant was designed to withstand has raised questions
                                   about whether a similar event could happen here. These questions were



                                   1
                                    Congress created NRC in 1974 to take over the regulatory duties of its predecessor, the
                                   Atomic Energy Commission.




                                   Page 1                                        GAO-12-465 Nuclear Regulatory Commission
further highlighted by natural hazards that affected the sites of several
U.S. commercial nuclear power plants and their reactors in 2011, 2
including flooding near two power plants in Nebraska, severe storms at a
plant in Alabama, and an earthquake at a plant in Virginia. 3

NRC’s design criteria for nuclear power reactors require that systems,
structures, and components important to safety be designed to withstand
the effects of natural hazards, such as earthquakes, tornados, hurricanes,
floods, and tsunamis, without losing the ability to perform their safety
functions. 4 The companies licensed to operate nuclear power reactors, or
licensees, are responsible for protecting their reactors against natural
hazards by assessing the hazards their reactors may face according to
these criteria and designing their reactors to withstand such hazards.
NRC is responsible for reviewing assessments and the resulting reactor
designs as part of its process for issuing licenses for the construction and
operation of nuclear power reactors, as well as for providing continuing
oversight of operating reactors.

Most of NRC’s regulatory framework—including its criteria for assessing
natural hazards for currently-operating reactors—was developed
according to a deterministic approach. The deterministic approach
establishes a specific set of potential accidents, the consequences of
which a nuclear power reactor must be designed to prevent or mitigate to
protect public health and safety. It also establishes requirements for
engineering safety margins and quality assurance standards for the
design, manufacture, and construction of nuclear power reactors. Using
this approach, NRC developed regulatory requirements primarily based
on historical experience, test results, and expert judgment without




2
 In this report, when we use the term power plant, we are referring to an entire site, and
nuclear power reactors are the individual units at each site.
3
 Each plant successfully withstood these events, although the ground accelerations of the
earthquake that affected the North Anna Power Station in Virginia exceeded the plant’s
design at several frequencies for a short period of time. This was the first time an
operating reactor in the United States exceeded its design limit for ground acceleration.
NRC and licensee inspections found minimal earthquake damage to the plant.
4
 10 C.F.R. Part 50, Appendix A, General Design Criterion 2—Design Bases for Protection
Against Natural Phenomena. According to an NRC document, all currently operating
reactors were licensed to or meet the intent of the General Design Criteria, which include
General Design Criterion 2.




Page 2                                          GAO-12-465 Nuclear Regulatory Commission
considering quantitative estimates of risk. 5 According to NRC documents,
in developing those requirements, NRC considered the concept of
“defense-in-depth”—a way of designing and operating nuclear power
reactors that focuses on creating multiple independent and redundant
layers of defense to compensate for potential human and mechanical
failures so that no single layer, no matter how robust, is exclusively relied
upon. 6 The agency has been moving since the 1990s toward a risk-
informed, performance-based approach to regulatory decision making
that is being implemented in phases according to NRC documents. 7 This
approach extends the traditional deterministic approach in part by
incorporating probabilistic risk assessment (PRA). PRA is a systematic
method for assessing what can go wrong, its likelihood, and its potential
consequences to determine quantitative estimates of risk in order to
provide insights into the strengths and weaknesses of the design and
operation of a nuclear power reactor. We have previously reported on
NRC’s use of PRA, its adoption of a risk-informed, performance-based
approach, and the challenges involved in implementing that approach. 8

According to several experts in assessing nuclear reactor risks, risk
analysts face challenges in assessing the threats posed by natural
hazards, particularly for extreme natural hazards with a low likelihood of
occurring but potentially high consequences. These challenges include
uncertain knowledge about particular natural hazards due to the limited



5
 According to NRC, the deterministic approach considers implied but unquantified
elements of probability in the selection of accidents to be analyzed.
6
 According to NRC, the “defense-in-depth” concept is not defined in NRC regulations, and
there is no single, agency-accepted description of the concept. However, it includes the
use of access controls, physical barriers, redundant and diverse key safety functions, and
emergency response measures.
7
 NRC differentiates between “risk-informed” and “risk-based” regulation, noting that the
former uses risk analysis to augment other information used to support regulatory
decisions, while the latter approach relies solely on quantitative results of risk
assessments. NRC does not endorse a risk-based approach.
8
 GAO, Nuclear Safety: NRC’s Oversight of Fire Protection at U.S. Commercial Nuclear
Reactor Units Could Be Strengthened, GAO-08-747 (Washington, D.C.: June 30, 2008);
GAO, Nuclear Regulatory Commission: Oversight of Nuclear Power Plant Safety Has
Improved, but Refinements Are Needed, GAO-06-1029 (Washington, D.C.: Sept. 27,
2006); GAO, Nuclear Regulation: Strategy Needed to Regulate Safety Using Information
on Risk, GAO/RCED-99-95 (Washington, D.C.: Mar. 19, 1999); GAO, Probabilistic Risk
Assessment: An Emerging Aid to Nuclear Power Plant Safety Regulation,
GAO/RCED-85-11 (Washington, D.C.: June 19, 1985).




Page 3                                         GAO-12-465 Nuclear Regulatory Commission
historical record and the rarity of extreme natural hazards, the developing
state of knowledge about natural hazards that varies by hazard, and
changes to natural hazards over time potentially due to climate change
and other causes.

Natural hazard assessments are only one component of NRC’s
processes for ensuring that nuclear power reactors are protected against
such hazards. In addition to requiring licensees to design their reactors
using information from such assessments, NRC also requires licensees to
have the ability to mitigate the consequence of accidents if they occur to
prevent core damage and the uncontrolled release of radioactive material
into the environment and, if that fails, to have emergency preparedness
procedures in place to mitigate the effects of a radiological release on the
public and the environment. Operating a nuclear power reactor is never
entirely free of risk; assessments do not eliminate all risk no matter how
well the hazards have been assessed but are an important source of
information for identifying and mitigating vulnerabilities to events that can
occur as a result of natural hazards.

In this context, you asked us to review how NRC assesses the threats
that natural hazards pose to operating U.S. commercial nuclear power
reactors. This report examines (1) the extent to which PRA is applied to
natural hazards at operating U.S. nuclear power reactors and (2) expert
views on and suggested changes, if any, to NRC processes for assessing
natural hazards at operating U.S. nuclear power reactors.

To describe the extent to which PRA is applied to natural hazards at
operating U.S. nuclear power reactors, we reviewed relevant documents
and data obtained from NRC and selected licensees. We interviewed
knowledgeable officials about the data and found the data to be
sufficiently reliable for the purposes of our report. We reviewed NRC
policies and procedures, as well as NRC initiatives related to the
assessment of natural hazards. We also reviewed the NRC task force
report on lessons learned from the Fukushima Daiichi disaster and
documented actions NRC has taken on recommendations related to the
assessment of natural hazards. In addition, we visited a nonprobability
sample of five nuclear power plants to interview licensees about the




Page 4                                 GAO-12-465 Nuclear Regulatory Commission
actions they have taken to assess natural hazards. 9 The five nuclear
power plants we visited were the Browns Ferry Nuclear Plant in Alabama,
the Diablo Canyon Power Plant in California, the North Anna Power
Station in Virginia, the San Onofre Nuclear Generating Station in
California, and the Turkey Point Nuclear Plant in Florida. We selected
these sites to capture a variety of characteristics, including reactor and
containment vessel type, operating license issuance date, license
renewal status, and natural hazard activity level. We also interviewed
NRC officials and representatives from the nuclear power industry, 10
public interest groups, and the insurance industry to discuss NRC
processes for assessing natural hazards. Further, we interviewed officials
and reviewed documents from the National Oceanic and Atmospheric
Administration, the U.S. Army Corps of Engineers, and the U.S.
Geological Survey on the current state of knowledge on natural hazards,
how that knowledge has changed over time, and the related uncertainty.

To obtain expert views on and suggested changes, if any, to NRC
processes for assessing natural hazards at operating U.S. nuclear power
reactors, we held semistructured interviews with 15 experts in assessing
natural hazards, risks to nuclear power reactors, or both. We identified
these experts through a literature search, a review of prior GAO reports,
and congressional and NRC hearings, as well as expert
recommendations. The experts we interviewed included representatives
from academia, government, industry, and public interest groups. We
analyzed experts’ responses across a standard set of questions and
summarized the results. We did not independently evaluate the quality of
NRC processes for assessing natural hazards and the threats they pose
to nuclear power reactors. Appendix I presents a more detailed
description of our scope and methodology and appendix II lists the names
and affiliations of the 15 experts we interviewed.

We conducted this performance audit from May 2011 to April 2012 in
accordance with generally accepted government auditing standards.
Those standards require that we plan and perform the audit to obtain



9
  Because this was a nonprobability sample, the information we gathered from these site
visits is not generalizable to all 65 operating nuclear power plants but provides important
illustrative information.
10
  We interviewed officials from the Nuclear Energy Institute, the policy organization of the
nuclear energy and technologies industry.




Page 5                                          GAO-12-465 Nuclear Regulatory Commission
                        sufficient, appropriate evidence to provide a reasonable basis for our
                        findings and conclusions based on our audit objectives. We believe that
                        the evidence obtained provides a reasonable basis for our findings and
                        conclusions based on our audit objectives.


                        This section discusses U.S. commercial nuclear power reactors, NRC’s
Background              approach to natural hazard assessments, NRC’s endorsement of PRA,
                        and actions NRC has taken on natural hazard assessments since the
                        Fukushima Daiichi disaster.


Commercial Nuclear      Currently, 104 commercial nuclear power reactors operate in the United
Power Reactors in the   States. Together, these reactors generated almost 20 percent of our
United States           nation’s electricity in 2011. These reactors are located at 65 power plants
                        across the country (see fig. 1) and are operated by 26 different
                        companies. All 104 operating reactors received their construction permits
                        in the 1960s and 1970s, with most receiving their operating licenses in
                        the 1970s and 1980s. 11 Many reactors are reaching or have reached the
                        end of their initial 40-year license. As of March 2012, NRC had renewed
                        71 reactor licenses for an additional 20 years and was currently reviewing
                        11 license renewal applications. 12 In addition, NRC authorized two new
                        reactors in Georgia in February 2012 and two new reactors in South
                        Carolina in March 2012 and is considering 10 applications for the building
                        and operation of new commercial nuclear power reactors.




                        11
                           One operating reactor received its operating license in 1969, and 6 operating reactors
                        received their operating licenses in the 1990s, with the last of those reactors receiving its
                        operating license in 1996. The other 97 operating reactors received their operating
                        licensees between 1970 and 1989.
                        12
                          NRC issues licenses for commercial nuclear power reactors to operate for 40 years.
                        Under current regulations, licensees may renew their licenses for up to 20 years. License
                        renewal focuses on evaluating and managing the adverse effects of aging on a nuclear
                        power reactor. Current regulations do not include a requirement that licensees of
                        operating reactors reevaluate their design bases pertaining to natural hazards as part of
                        the license renewal process.




                        Page 6                                           GAO-12-465 Nuclear Regulatory Commission
Figure 1: U.S. Operating Commercial Nuclear Power Reactors by Power Plant Location




NRC’s Approach to                      NRC required licensees of the 104 operating reactors to use deterministic
Assessing Natural Hazards              analysis to assess the natural hazards their reactors might face as part of
                                       their construction permit and operating license applications. 13 Among
                                       other things, NRC required the designs of structures, systems, and


                                       13
                                         10 C.F.R. Part 50, Appendix A and 10 C.F.R. Part 100—Reactor Site Criteria. NRC
                                       requires new nuclear power reactors licensed after January 1997 to be sited and designed
                                       with respect to geological and seismic determinations based on an appropriate analysis,
                                       such as a probabilistic seismic hazard analysis. 10 C.F.R. Part 100, subpart B.




                                       Page 7                                       GAO-12-465 Nuclear Regulatory Commission
components important to safety to reflect appropriate consideration of the
most severe natural hazards that had been historically reported for a
reactor site and the surrounding area, with sufficient safety margin to
account for the limited accuracy, quantity, and period over which historical
data on natural hazards have been accumulated. NRC staff
independently reviewed applicants’ natural hazard assessments as part
of the application review process to determine whether the assessments
were acceptable. When NRC issued an operating license for a nuclear
power reactor, these natural hazard assessments became part of the
reactors’ licensing basis––that is, the collection of documents or technical
criteria upon which NRC issues licenses for the construction and
operation of nuclear power reactors. NRC does not require licensees to
reevaluate their natural hazard assessments on a periodic basis, but
through several pieces of regulation it requires that licensees consider
new information on natural hazards as they become aware of it to
determine if the information may necessitate additional licensee action
under NRC requirements. NRC staff also continually evaluate new
information on natural hazards through research and oversight processes
to assess potential impacts on reactor safety, according to NRC officials,
and the agency has initiated several discrete efforts over time that have
examined the threats that natural hazards pose to operating nuclear
power reactors. For example, in 1991, NRC requested that each licensee
identify and report plant-specific vulnerabilities to severe accidents
caused by external events, including natural hazards, as part of its
Individual Plant Examination of External Events (IPEEE) program. 14 More
recently, NRC initiated the Generic Issue-199 program in 2005 to
examine the implications of new seismic hazard estimates for the central
and eastern United States for operating nuclear power reactors. 15




14
  NRC, Individual Plant Examination of External Events (IPEEE) for Severe Accident
Vulnerabilities—10 CFR 50.54(f), Generic Letter No. 88-20, Supplement 4 (Washington,
D.C.: June 28, 1991). Acts of sabotage or terrorism were not included in the set of events
considered.
15
 NRC, Implications of Updated Probabilistic Seismic Hazard Estimates in Central and
Eastern United States, Generic Issue 199 (Washington, D.C.: June 9, 2005).




Page 8                                         GAO-12-465 Nuclear Regulatory Commission
NRC’s Endorsement of   NRC’s approach to risk assessment has evolved over time. 16 NRC began
PRA                    endorsing the use of PRA to enhance and extend traditional deterministic
                       analysis as part of the agency’s move toward a risk-informed,
                       performance-based regulatory approach. Specifically,

                       •    In 1986, NRC issued a policy statement calling for the use of PRA to
                            measure achievement of the agency’s individual and societal safety
                            goals. 17 The policy statement aimed to express NRC policy on “how
                            safe is safe enough” at U.S. nuclear power plants by broadly defining
                            an acceptable level of radiological risk that might be imposed on the
                            public as a result of plant operations. 18

                       •    In 1995, NRC issued a policy statement encouraging the increased
                            use of PRA in all regulatory matters to the extent supported by the
                            state-of-the-art in PRA methods and data, and in a manner that
                            complemented NRC’s deterministic approach and supported NRC’s
                            defense-in-depth philosophy. 19




                       16
                         Appendix III describes key developments in NRC’s approach to probabilistic risk
                       assessment, including its application to natural hazards.
                       17
                        NRC, Safety Goals for the Operations of Nuclear Power Plants; Policy Statement, 51
                       Fed. Reg. 30,028 (Aug. 21, 1986).
                       18
                          The policy statement established two qualitative safety goals—one addressing individual
                       risk and the other addressing societal risk—each supported by a quantitative health
                       effects objective by which the safety goal could be measured. NRC staff subsequently
                       adopted subsidiary numerical objectives of less than 1 core damage event expected per
                       10,000 years of reactor operation and less than 1 large early radiation release expected
                       per 100,000 years of reactor operation to serve as surrogates for the quantitative health
                       effects objectives. Both the quantitative health effects objectives and the subsidiary
                       numerical objectives are calculated using probabilistic risk assessment. The safety goals,
                       quantitative health effects objectives, and subsidiary numerical objectives are applied at
                       the individual reactor level. NRC officials indicated that NRC does not consider aggregate,
                       industry-wide probabilities that core damage or a large early radiation release would occur
                       somewhere in the United States or set total aggregate, industry-wide objectives because
                       NRC licenses nuclear power reactors on an individual reactor basis and because they do
                       not believe such probabilities would be appropriate.
                       19
                         NRC, Use of Probabilistic Risk Assessment Methods in Nuclear Regulatory Activities;
                       Final Policy Statement, 60 Fed. Reg. 42,622 (Aug. 16, 1995).




                       Page 9                                         GAO-12-465 Nuclear Regulatory Commission
•     In 2007, NRC issued regulations requiring applicants for combined
      licenses 20 for new nuclear power reactors to submit a description and
      the results of a reactor-specific PRA to NRC as part of their
      application. 21 NRC also began requiring licensees of new nuclear
      power reactors that will operate those reactors under a combined
      license to develop, maintain, and periodically upgrade a reactor-
      specific PRA. Among other things, NRC required the PRA to cover
      initiating events––that is, events that can lead to a reactor accident—
      for which there were NRC-endorsed consensus standards for PRA
      quality. 22

•     In 2009, NRC issued a regulatory guide that endorsed national
      consensus standards for PRA quality. 23 Effective April 2010, licensees
      of operating reactors who choose to submit risk-informed licensing
      applications are expected to meet the NRC-endorsed guidelines,
      including a quality standard that addresses the assessment of natural
      hazards.

•     In 2011, the Chairman of the NRC commissioned a task force to
      develop a strategic vision and assess options for a more holistic risk-
      informed, performance-based regulatory approach, with one option
      being better incorporation of risk management concepts into NRC’s
      regulatory programs.




20
   In 1989, NRC promulgated 10 C.F.R. Part 52, which established a new combined
license for electric power companies to obtain a license to build and operate a new
reactor. 54 Fed. Reg. 15,372 (Apr. 18, 1989). While NRC has revised its regulatory
process, the technical bases for its decisions to make findings have generally remained
the same. The combined license is NRC’s response to the nuclear industry’s concerns
about the length and complexity of NRC’s former two-step process of issuing a
construction permit followed by an operating license. The combined license process
provides a one-step approval process that authorizes a licensee to construct and operate
a nuclear power reactor; as such, it is intended to provide predictability and early
resolution of issues in the review process.
21
    10 C.F.R. § 52.79(a)(46).
22
    10 C.F.R. § 50.71(h).
23
 NRC, An Approach for Determining the Technical Adequacy of Probabilistic Risk
Assessment Results for Risk-Informed Activities, Regulatory Guide 1.200 (Washington,
D.C.: March 2009).




Page 10                                       GAO-12-465 Nuclear Regulatory Commission
NRC policy statements, training manuals, and other documents cite
numerous advantages of using PRA to enhance the agency’s traditional
deterministic approach. Specifically, PRA

•    can enhance safety decision making with risk insights, allowing for the
     more efficient use of NRC resources and reducing unnecessary
     burdens on licensees;

•    explicitly considers a broader set of potential challenges to safety;

•    provides a logical means for prioritizing challenges based on risk
     significance, operating experience, and engineering judgment;

•    explicitly identifies, evaluates, and quantifies sources of uncertainty;

•    provides a means to test the sensitivity of assessment results to key
     assumptions;

•    provides a rigorous, systematic tool for analyzing complex systems
     and enables information integration; and

•    provides qualitative insights into plant vulnerabilities and quantitative
     results for use in decision making.

NRC has encouraged the increased use of PRAs in all regulatory matters
but generally does not require licensees to develop or maintain PRAs for
currently operating reactors. However, licensees may choose to submit
license amendment requests so they can transition to less prescriptive,
risk-informed approaches for particular issues allowed by NRC
regulations, such as NRC’s risk-informed approach to fire protection. 24
According to NRC officials, if licensees choose to apply to use a risk-
informed approach, licensees must develop a PRA to the extent required



24
  In 2004, NRC issued a regulation that allowed the transition of nuclear reactors from its
existing, prescriptive fire safety regulations to a less prescriptive, risk-informed,
performance-based approach, under which licensees can use tools, such as fire modeling
and risk analysis, to determine which areas of the nuclear power plant are most at risk
from fire. According to NRC officials, these analyses could enable units to focus their
resources on addressing these higher-risk areas and reduce the number of future
exemptions in areas that are no longer considered to be at high risk from fire. Reductions
in exemptions would, thus, simplify the units’ licenses. For more information, see
GAO-08-747.




Page 11                                        GAO-12-465 Nuclear Regulatory Commission
for the application. 25 In contrast, applicants for combined licenses to build
and operate new nuclear power reactors are required to develop a PRA in
addition to a deterministic analysis. 26 For combined licenses, NRC
expects those PRAs to address natural hazards except for natural
hazards that licensees determine are an insignificant contributor to risk,
based on NRC-endorsed screening criteria. For example, a nuclear
power reactor that is distant from a coast will likely be able to omit
tsunami hazards from its PRA. Further, NRC requires licensees of new
nuclear power reactors who will operate their reactors under a combined
license to develop, maintain, and periodically upgrade their PRAs over
the operating life of their reactors. 27 PRAs are used to evaluate several
categories of initiating events, including internal events, which start inside
the nuclear power plant or the electric system serviced by the power plant
(e.g., random hardware failures and operator actions), and external
events, which typically start outside the nuclear power plant, such as
natural hazards (e.g., earthquakes, external floods, external fires, and
high-wind events). According to NRC documents, PRA can estimate three
different levels of risk—one focused on reactor core damage, one
focused on containment release, and one focused on radiological




25
   Regulatory activities that use PRA include (1) risk-informed licensing change
applications; (2) categorization and treatment of structures, systems, and components
under 10 C.F.R. § 50.69; (3) fire protection programs under 10 C.F.R. § 50.48(c); and (4)
licenses, certifications, and approvals for nuclear power plants under 10 C.F.R. Part 52.
NRC staff have prepared guidance to assist licensees in developing risk-informed
changes to their licensing bases. See NRC, An Approach to Using Probabilistic Risk
Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis,
Regulatory Guide 1.174 (Washington, D.C.: July 1998).
26
 10 C.F.R. § 52.79(a)(46).
27
  Specifically, NRC requires licensees who will operate reactors under a combined license
to develop, maintain, and periodically upgrade a Level 1 and Level 2 PRA. 10 C.F.R. §
50.71(h).




Page 12                                       GAO-12-465 Nuclear Regulatory Commission
                           consequences to the public. 28 For information on developing a PRA, see
                           appendix IV.


Actions NRC Has Taken on   In March 2011, NRC chartered a staff task force to review its processes
Natural Hazard             and regulations in light of the Fukushima Daiichi disaster and to
Assessments Since the      recommend whether NRC should make near-term improvements to its
                           regulatory system. 29 The task force issued its final report in July 2011.
Fukushima Daiichi
                           Among other things, the task force found that NRC regulations and
Disaster                   guidance provide a robust approach for assessing natural hazards, but it
                           noted that NRC’s processes for assessing natural hazards had evolved
                           over time. As a result, the licensing bases, design, and level of protection
                           from natural hazards differ among operating reactors depending on when
                           the reactors were built and when they were licensed for operation. Based
                           on these findings, the task force recommended, among other things, that
                           NRC order licensees to reevaluate the seismic and flooding hazards at
                           their sites against current NRC requirements and guidance and, if
                           necessary, update their reactor design bases. The task force further
                           recommended that NRC initiate rulemaking to require licensees to
                           confirm seismic and flooding hazards every 10 years, address any new
                           and significant information and, if necessary, update their reactor design
                           bases. In addition, the task force recommended that, while these longer
                           term actions are being completed, NRC order licensees to check their
                           seismic and flood protection features to identify and address any plant-


                           28
                             Specifically, Level 1 PRAs evaluate events that can lead to plant accidents and examine
                           reactor systems and operators’ responses to calculate “core damage frequency”—the
                           frequency of the combinations of initiating events, hardware failures, and human errors
                           leading to the uncovering of the reactor core such that reflooding of the core is not
                           imminent. Level 2 PRAs start with Level 1 core damage accidents and assess the
                           frequencies of various categories of containment releases. The results for operating
                           reactors are typically reported in terms of “large early release frequency”—the frequency
                           of those accidents leading to significant, unmitigated releases from the reactor’s
                           containment in a time frame prior to effective evacuation of the nearby population such
                           that there is a potential for early health effects. Level 3 PRAs start with Level 2 radiological
                           release accidents and assess the public health consequences of a radiological release in
                           terms of injury to the public and damage to the environment. Because core damage and
                           large early release estimates are easier to calculate than public health consequences, the
                           results of Level 1 and Level 2 PRAs are often used as surrogates for the results of a Level
                           3 PRA. NRC has plans to perform a new Level 3 PRA (including Level 1 and Level 2
                           PRAs) for a single operating power plant that will include assessment of natural hazards
                           and be completed within 4 years.
                           29
                             Appendix V describes actions that NRC has taken in response to the Fukushima Daiichi
                           disaster that relate to natural hazard assessments.




                           Page 13                                          GAO-12-465 Nuclear Regulatory Commission
specific vulnerabilities and verify the adequacy of monitoring and
maintenance for protection features such as watertight barriers and seals.

In response to the task force report, in August 2011, NRC directed
agency staff to identify the task force recommendations that could and, in
the staff’s view, should be implemented without unnecessary delay. The
staff submitted a report to NRC in October 2011 with their proposed
prioritization of the recommendations. In this report, the staff
recommended that NRC move forward with requiring licensees to
reevaluate the seismic and flooding hazards at their sites and to check
their seismic and flood protection features. However, the staff
recommended that NRC wait to initiate rulemaking requiring licensees to
confirm their sites’ seismic and flooding hazards every 10 years in order
to gain experience from the implementation of the initial reevaluation. In
December 2011, NRC approved the staff’s proposals and supported
actions on several recommendations. That same month, Congress
passed, and the President signed, the 2012 Consolidated Appropriations
Act, which included a provision directing NRC to require that licensees
reevaluate external hazards at their sites, including seismic and flooding
hazards, as expeditiously as possible. 30 In February 2012, NRC staff
proposed issuing a request for information that, among other things,
would ask licensees to reevaluate the seismic and flooding hazards at
their sites. 31 The staff suggested PRA as one of two acceptable methods
for licensees to use in reevaluating seismic hazards. The staff did not
exclude, but also did not suggest, PRA as a method for assessing
flooding hazards because, according to NRC officials, NRC currently uses
a deterministic approach for assessing flooding hazards. NRC staff also
proposed addressing other natural hazards, such as wind and missile
loads from tornados and hurricanes, at a later date once sufficient
resources are available for the reevaluations. According to NRC officials,
it is not clear yet whether agency staff will suggest licensees use PRA or
other methods to reevaluate those other natural hazards. In March 2012,




30
  Consolidated Appropriations Act, 2012, Pub. L. No. 112-74, Div. B, § 402 (Dec. 23,
2011).
31
  NRC, Proposed Orders and Requests for Information in Response to Lessons Learned
from Japan’s March 11, 2011, Great Tohoku Earthquake and Tsunami, SECY-12-0025
(Washington, D.C.: Feb. 17, 2012).




Page 14                                       GAO-12-465 Nuclear Regulatory Commission
                          NRC issued the request for information proposed by agency staff in
                          February. 32


                          Licensees and NRC apply PRA to natural hazards at operating U.S.
PRA Is Applied to         nuclear power reactors to a limited extent, according to information
Natural Hazards to a      provided by nuclear power industry representatives, NRC officials, and
                          several experts in assessing nuclear reactor risks that we interviewed and
Limited Extent            data we obtained. While NRC has endorsed PRA as a means to enhance
                          and extend traditional deterministic assessments, the agency has not
                          conducted the analyses to determine whether or not it should require
                          licensees of operating reactors to develop and maintain PRAs that
                          address natural hazards.


Licensees and NRC Apply   Nuclear power industry representatives, NRC officials, and several
PRA to Natural Hazards    experts in assessing nuclear reactor risks we interviewed, as well as data
to a Limited Extent       we obtained, indicate that licensees and NRC apply PRA to natural
                          hazards at operating nuclear power reactors to a limited extent. Prior to
                          its response to the Fukushima Daiichi disaster, the last time NRC
                          requested licensees to assess natural hazards was in 1991 when the
                          agency initiated the IPEEE program. For the IPEEE, NRC requested each
                          licensee to voluntarily identify and report plant-specific vulnerabilities to
                          severe accidents caused by external events, including natural hazards.
                          Although PRA was suggested by NRC as one of several possible
                          methods for licensees to use in their examinations, most licensees opted
                          to use methods other than PRA. Specifically, NRC received 70 IPEEE
                          submissions from licensees covering all operating reactors. According to
                          NRC’s summary of the 70 submissions, about 40 percent applied PRA to
                          seismic hazards, and about 15 percent applied PRA to high winds, floods,
                          and other external events. NRC reported that almost no licensees
                          identified vulnerabilities with respect to seismic hazards, and none
                          identified vulnerabilities related to high winds, flooding, or other external
                          events. Nonetheless, according to NRC’s summary, 70 percent of the
                          IPEEE submissions identified plant improvements related to seismic
                          hazards, and about 50 percent identified plant improvements related to
                          high winds and flooding. NRC performed a review of all IPEEE


                          32
                            NRC, Staff Requirements—SECY-12-0025—Proposed Orders and Requests for
                          Information in Response to Lessons Learned From Japan’s March 11, 2011, Great
                          Tohoku Earthquake and Tsunami (Washington, D.C.: Mar. 9, 2012).




                          Page 15                                    GAO-12-465 Nuclear Regulatory Commission
submissions to assess the technical adequacy of the methods and data
used and noted that the quality of licensees’ submissions varied. NRC did
not attempt to verify or validate licensees’ results. NRC staff proposed in
2011 that licensees reevaluate seismic hazards under the agency’s
Generic Issue-199 program. Similar to the IPEEE, the proposal cited PRA
as one—but not the only—possible method for assessing seismic
hazards. The NRC staff has now proposed to pursue the reevaluation of
seismic hazards as part of the implementation of the Fukushima Daiichi
task force recommendations and has identified PRA as one of the
methods that licensees can choose to use.

Nuclear Energy Institute representatives told us that, if data were to be
collected on licensees’ current application of PRA to natural hazards, they
believe the data would likely show little difference since the IPEEE in the
1990s. They also stated that they believe few of those PRAs developed
for the IPEEE would have been updated since then. Likewise, senior
NRC officials told us that were NRC to obtain current data on licensees’
application of PRA to natural hazards, the results would likely show
limited application, substantial variability, and few new or updated
assessments since the IPEEE. According to several experts in assessing
nuclear reactor risks we spoke with, few of the nation’s operating reactors
currently have PRAs in place that address natural hazards. For example,
one expert stated that some reactors have PRAs that address seismic
hazards, and a few have PRAs that address external floods, but the rest
do not have PRAs that address natural hazards at all.

NRC does not collect comprehensive data on the extent of licensees’
voluntary application of PRA to natural hazards at operating reactors.
NRC officials stated that, because PRAs are not required for operating
reactors, NRC does not have comprehensive data on their use. NRC
officials told us that where licensees voluntarily undertake risk-informed
applications or license amendments, the information licensees submit to
NRC may include results on natural hazards. For example, when a
licensee chooses to use a risk-informed approach to request a change to
its licensing basis, the licensee must determine whether natural hazards




Page 16                               GAO-12-465 Nuclear Regulatory Commission
are a significant contributor to risk and provide that information to NRC. 33
To make this determination, the licensee may use a PRA. Apart from
these circumstances, however, NRC does not have data on operating
reactor licensees’ PRA use. NRC officials could not tell us, therefore,
which licensees of operating reactors have voluntarily undertaken PRAs
that address natural hazards, what natural hazards are addressed, when
existing PRAs were first developed and last updated, or the extent to
which they meet NRC-endorsed quality standards. Nuclear Energy
Institute representatives similarly told us that they do not collect data on
PRA use and do not have a plant-by-plant listing of which reactors have
PRAs in place that address natural hazards. NRC officials said that they
do not collect comprehensive PRA information because licensees of
operating reactors are not required to have a PRA. Further, they told us
that, if NRC decided to collect this information, the agency would likely
issue a “generic communication”––NRC’s primary method of
communicating information to licensees and interested stakeholders or
requesting information from them. NRC officials told us that a generic
communication to obtain comprehensive PRA information would take
NRC a significant amount of time to develop and issue. 34

According to representatives of five licensees we interviewed, 12 of the
25 reactors those licensees operate have PRAs in place that address
seismic hazards, and none have PRAs in place that address high winds
or external floods (see table 1). 35 The representatives told us that, in
some instances, a reactor does not have a PRA in place for a given
natural hazard because a screening analysis indicated that the hazard’s
contribution to risk was sufficiently low that it could be eliminated from


33
   NRC licenses nuclear power reactors on an individual reactor basis. Therefore,
licensees’ natural hazard assessments—including voluntary PRAs—and NRC’s review of
those assessments are at the individual reactor level and generally do not take into
account other nuclear power reactors on the same site, or other nuclear power plants in
the region or nationwide. An event that affects multiple reactors can potentially have
greater consequences than an event that affects a single reactor.
34
  Some generic communications request information or actions relative to NRC
regulations and require responses. Others suggest methods for meeting NRC
requirements on which licensees may voluntarily act or communicate related technical or
regulatory information.
35
  We requested data from the companies that operate the five nuclear power plants we
visited regarding their application of PRA to seismic hazards, floods, high winds, and other
external events at the reactors we toured, as well as the other reactors operated by the
companies.




Page 17                                        GAO-12-465 Nuclear Regulatory Commission
                                         further consideration; in other instances, licensees have performed
                                         margin studies instead or rely on traditional deterministic assessments of
                                         the hazard. Of the seismic PRAs in place at 12 of the 25 reactors for
                                         which we obtained information, 10 have not been updated since they
                                         were first developed. The seismic PRAs at 6 of the 12 reactors were
                                         developed in the 1990s under NRC’s IPEEE program. The seismic PRAs
                                         at the other reactors were developed between 1983 and 2010 for a
                                         variety of reasons. For example, two were developed as part of voluntary
                                         licensee efforts to better understand seismic risk. Another was developed
                                         as part of a plant’s long-term seismic monitoring program created as a
                                         condition of its operating license due to discovery during construction of a
                                         new fault line.

Table 1: Natural Hazard PRAs at Selected Nuclear Power Reactors

                                                              Natural hazards included
                  Plant name         Reactor                          High      External                       Last
                                            a
Licensee          (state)            number              Seismic      winds     floods        Developed        updated
Dominion          Kewaunee Power     Data not            Yes          No        No            1994             1994
                  Station (WI)       applicable
                  Millstone Power    2                   No           No        No            Data not         Data not
                  Station (CT)                                                                applicable       applicable
                                     3                   Yes          No        No            1995             1995
                  North Anna Power 1                     No           No        No            Data not         Data not
                  Station (VA)                                                                applicable       applicable
                                     2                   No           No        No            Data not         Data not
                                                                                              applicable       applicable
                  Surry Nuclear      1                   Yes          No        No            2010             2010
                  Power Station      2                   Yes          No        No            2010             2010
                  (VA)
NextEra Energy    Duane Arnold       Data not            Yes          No        No            1997             2005
                  Energy Center (IA) applicable
                  Point Beach        1                   Yes          No        No            1995             1995
                  Nuclear Plant (WI) 2                   Yes          No        No            1995             1995
                  Seabrook Station   1                   Yes          No        No            1983             2004
                  (NH)
                  St. Lucie Plant    1                   No           No        No            Data not         Data not
                  (FL)                                                                        applicable       applicable
                                     2                   No           No        No            Data not         Data not
                                                                                              applicable       applicable
                  Turkey Point       3                   No           No        No            Data not         Data not
                  Nuclear Plant (FL)                                                          applicable       applicable
                                     4                   No           No        No            Data not         Data not
                                                                                              applicable       applicable




                                         Page 18                                     GAO-12-465 Nuclear Regulatory Commission
                                                                           Natural hazards included
                    Plant name         Reactor                                           High           External                                        Last
                                              a
Licensee            (state)            number                         Seismic            winds          floods               Developed                  updated
Pacific Gas &       Diablo Canyon      1                              Yes                No             No                   1988                       1988
Electric            Power Plant (CA)   2                              Yes                No             No                   1988                       1988
Southern            San Onofre         2                              Yes                No             No                   1995                       1995
California Edison   Nuclear
                    Generating Station 3                              Yes                No             No                   1995                       1995
                    (CA)
Tennessee Valley    Browns Ferry       1                              No                 No             No                   Data not                   Data not
Authority           Nuclear Plant (AL)                                                                                       applicable                 applicable
                                       2                              No                 No             No                   Data not                   Data not
                                                                                                                             applicable                 applicable
                                       3                              No                 No             No                   Data not                   Data not
                                                                                                                             applicable                 applicable
                    Sequoyah Nuclear 1                                No                 No             No                   Data not                   Data not
                    Plant (TN)                                                                                               applicable                 applicable
                                       2                              No                 No             No                   Data not                   Data not
                                                                                                                             applicable                 applicable
                    Watts Bar Nuclear 1                               No                 No             No                   Data not                   Data not
                    Plant (TN)                                                                                               applicable                 applicable
                                           Sources: GAO analysis of data provided by Dominion, NextEra Energy, Pacific Gas & Electric, Southern California Edison, and
                                           Tennessee Valley Authority.

                                           a
                                            One or more reactors may be located at a single power plant. Generally, individual reactors are
                                           numbered. Where only one reactor is located at a plant, however, the reactor may or may not have a
                                           number associated with it.

                                           NRC has also applied PRA to natural hazards to a limited extent. For
                                           example, NRC officials told us that the agency has developed 16 external
                                           event risk analysis models of limited detail that address some natural
                                           hazards at 19 operating reactors. 36 These models are available to NRC
                                           staff for internal use in providing risk insights to various agency initiatives
                                           such as NRC’s inspection and incident investigation programs. According
                                           to NRC officials, NRC staff use the models to a limited extent. The
                                           models rely on licensee information, such as that derived from the IPEEE,
                                           that could be out-of-date. NRC officials told us they have plans to validate


                                           36
                                              In 1995, NRC began developing these models, called Standardized Plant Analysis Risk
                                           models. As of December 2011, NRC had 78 Standardized Plant Analysis Risk models that
                                           address internal events at all 104 operating reactors and 16 Standardized Plant Analysis
                                           Risk models that address some external events at 19 operating reactors. Specifically, of
                                           the 16 external event Standardized Plant Analysis Risk models, all 16 include seismic
                                           events among the natural hazards assessed, 5 include high winds, and 2 include external
                                           floods.




                                           Page 19                                                             GAO-12-465 Nuclear Regulatory Commission
                            the models in the future to improve confidence among agency staff in
                            their use. According to the officials, there has also recently been renewed
                            interest in the agency in resuming development of these models for the
                            remaining operating reactors. The officials told us NRC is finalizing the
                            first in a series of such models that include more recent plant information
                            and improved validation. 37 In a separate initiative, according to NRC
                            documents and officials, NRC has plans to perform a new full-scope PRA
                            for a single operating power plant that will calculate off-site risk and its
                            contributors, including natural hazards. 38 NRC staff identified several
                            reasons for doing so, including technical advances that had taken place
                            since the last similar NRC effort in the late 1980s, 39 scope considerations
                            that had not previously been addressed such as multiunit site effects, and
                            potential future uses for these models such as verifying or revisiting
                            regulatory requirements and guidance and developing NRC’s in-house
                            PRA technical capability.


NRC Has Not Analyzed        While NRC has endorsed PRA as a means to enhance and extend
Whether It Should Require   traditional deterministic assessments, the agency has not conducted the
PRAs That Address           analyses to determine whether or not it should require licensees of
                            operating reactors to develop and maintain PRAs that address natural
Natural Hazards             hazards. NRC’s “backfit rule” generally requires NRC to assure licensees
                            that requirements placed on them will change only when warranted from




                            37
                              NRC officials told us the 19 reactors that the existing Standardized Plant Analysis Risk
                            external event models were developed for were selected on the basis of convenience and
                            availability of information. NRC’s initial plans to develop additional external event
                            Standardized Plant Analysis Risk models for the remaining reactors were not carried out
                            due to an agency determination that resources would be better allocated to internal event
                            Standardized Plant Analysis Risk model development.
                            38
                               In September 2011, the NRC directed agency staff to plan for and perform a new full-
                            scope comprehensive site Level 3 PRA for a single operating power plant that will include
                            assessment of natural hazards and be completed within 4 years. A full-scope
                            comprehensive site Level 3 PRA is a PRA that includes a quantitative assessment of the
                            public risk from accidents involving all site reactor cores and spent nuclear fuel that can
                            occur during any plant operating state, and that are caused by all initiating event hazards
                            (internal events, fires, flooding, seismic events, and other site-specific external hazards).
                            39
                             NRC, Severe Accident Risks: An Assessment for Five U.S. Nuclear Power Plants,
                            NUREG-1150 (Washington, D.C.: December 1990).




                            Page 20                                         GAO-12-465 Nuclear Regulatory Commission
a public health and safety standpoint. 40 As such, to require that licensees
of operating reactors apply PRA to natural hazards, NRC officials told us
NRC would have to determine that the advantages of doing so are
necessary to ensure that protection of the public health and safety is
adequate or that the added increase in overall protection is at least
substantial and justifies the cost of implementation. Senior NRC officials
told us that it may be difficult to meet either of these criteria in order to
justify the imposition of a new PRA requirement on licensees of operating
reactors. 41 NRC officials we spoke with were unaware of any formal
determinations by the agency regarding whether or not requiring PRA of
operating reactors meets the backfit rule or exceptions thereto.
Additionally, an official from the agency’s Office of General Counsel told
us that the NRC has the authority to “administratively except” a new




40
  NRC’s backfit rule requires that NRC determine that new requirements would result in a
substantial increase in the overall protection of public health and safety or common
defense and security and that this increased protection justifies the cost of
implementation. 10 C.F.R. § 50.109(a)(3). Backfit is defined in 10 C.F.R. § 50.109(a)(1) as
“the modification of or addition to systems, structures, components, or design of a facility;
or the design approval or manufacturing license for a facility; or the procedures or
organization required to design, construct or operate a facility; any of which may result
from a new or amended provision in the Commission’s regulations or the imposition of a
regulatory staff position interpreting the Commission’s regulations that is either new or
different from a previously applicable staff position.” The backfit rule requires a backfit
analysis demonstrating that the new or changed requirement is a substantial increase in
overall protection unless NRC finds that a backfit is needed to ensure that protection of
public health and safety is adequate, or in other limited situations. 10 C.F.R. §
50.109(a)(4).
41
  We reported in 1999 that similar difficulties had been expressed by the NRC staff in the
1990s, during which time NRC was considering whether and to what extent it should
revise its regulations pertaining to operating reactors to make them risk-informed. In 1998,
agency staff proposed to the NRC a phased approach to risk-informing its regulations.
The staff also recommended that implementation of revised regulations be voluntary. The
staff noted that it would be difficult to make the backfit determination needed to require
implementation and further that doing so could create the impression that current plants
were less safe. In response, the Chairman suggested a more aggressive approach that
would entail a risk-informed approach for all relevant regulations across the board and
stated that the revised regulations should be mandatory, unless the staff found that backfit
provisions could not be met. Also, the Commissioners expressed concern about a
voluntary approach, believing that it would create two classes of plants operating under
two different sets of regulations. Ultimately, however, the NRC adopted the staff’s
proposed phased approach to risk-informing its regulations of operating reactors and
determined that compliance would be voluntary.




Page 21                                         GAO-12-465 Nuclear Regulatory Commission
                          requirement from the backfit rule. 42 NRC officials stated that it generally
                          takes several years to conduct and document the regulatory analyses to
                          determine whether a new requirement should be implemented and then
                          to complete the rulemaking process necessary before a requirement can
                          become law. 43


                          The 15 experts in assessing natural hazards and/or nuclear reactor risks
Experts Offered a         that we interviewed offered a range of views on (1) the adequacy of NRC
Range of Views on         processes for assessing the threats that natural hazards pose to
                          operating U.S. nuclear power reactors and (2) what, if any, changes to
NRC Assessment            those processes are warranted. Experts had varied views on the overall
Processes                 adequacy of NRC natural hazard assessment processes and identified a
                          number of strengths and limitations of those processes. More than half of
                          the experts we interviewed suggested expanding the use of PRA for
                          assessing natural hazards as a complement to traditional deterministic
                          analyses, and several experts cited a number of challenges to doing so.
                          Some experts we interviewed suggested other changes to NRC
                          processes for assessing natural hazards. Appendix II lists the names and
                          affiliations of the 15 experts we interviewed.


Experts Noted Strengths   The 15 experts we interviewed had varied views on the overall adequacy
and Limitations of NRC    of NRC processes for assessing the threats that natural hazards pose to
Assessment Processes      operating U.S. nuclear power reactors and identified a number of
                          strengths and limitations of those processes. Several experts said they
                          believe NRC processes are generally adequate. One of those experts
                          noted that, in his view, NRC’s processes for assessing natural hazards
                          work well due to the conservative approach NRC takes to assessing and
                          designing against natural hazards. Another expert who agreed that NRC
                          processes are adequate overall explained that natural hazards are well


                          42
                            The official told us that the NRC did this when it adopted the Aircraft Impact Assessment
                          Rule in 2009. See 74 Fed. Reg. 28,112, 28,143 (June 12, 2009). The official stated that an
                          administrative exception must be the subject of notice and public comment for
                          rulemakings, but is not required with respect to the issuance of orders.
                          43
                            Officials from NRC’s Office of General Counsel believe that a requirement to perform a
                          PRA would not be subject to the backfit rule because such a requirement would constitute
                          an information collection (and possibly reporting) requirement that NRC has deemed not
                          to be subject to the backfit rule. However, according to the same officials, if the
                          requirement is implemented by rule, the NRC would prepare—as part of that rulemaking—
                          a regulatory analysis to support the adoption of such a requirement.




                          Page 22                                        GAO-12-465 Nuclear Regulatory Commission
accounted for in reactor designs and that NRC does as good of a job as
any other federal agency in ensuring that its regulated community
protects against natural hazards. Several other experts expressed mixed
views on the adequacy of NRC processes. Some of these experts stated
that they had more confidence in NRC’s approach for assessing the
threats that natural hazards pose to proposed new reactors than its
approach for operating nuclear power reactors because the former
requires licensees to use PRA in addition to traditional deterministic
assessments when assessing natural hazards. Two experts stated that
NRC processes for assessing natural hazards are inadequate. One of
those experts noted that NRC and licensees need to consider other
possibilities that may affect natural hazard assessments, such as the
potential effects of climate change on the natural hazards a reactor may
face over its operating life.

Experts we interviewed identified a number of strengths of NRC
processes for assessing the threats posed by natural hazards to
operating nuclear power reactors. Four strengths were identified by more
than two experts. First, about half of the experts identified as a strength
the structured and thorough process NRC follows in reviewing licensee
assessments of natural hazards. A few of these experts noted the
stringency of NRC’s review of licensee assessments, and a few others
said that the agency has done an effective job defining a comprehensive
set of natural hazards that licensees are responsible for assessing.
Second, several experts identified as a strength what they said was
NRC’s conservative approach to licensee assessments and reactor
designs for natural hazards, including NRC’s emphasis on (1) defense-in-
depth principles, (2) engineering safety margins, and (3) reactor designs
based on the worst credible natural hazards a site is expected to face.
Some of these experts said that, because NRC’s approach to assessing
natural hazards is conservative, they believe that U.S. nuclear power
reactors are well-designed and well-protected from natural hazards.
Third, a few experts pointed to the expertise of NRC’s staff in assessing
natural hazards as another strength of the agency’s processes. These
experts said that NRC staff are diligent in trying to understand natural
hazards and are proactive in identifying new information for assessing
natural hazards. Several experts indicated that NRC is effective at
identifying and considering new natural hazard data, although one of
those experts also noted that it can take the agency time to incorporate
new data into agency regulations. Fourth, a few experts identified as a
strength what they said was NRC’s global leadership in developing the
latest tools and methods for assessing the threats posed by natural
hazards to nuclear power reactors.


Page 23                                GAO-12-465 Nuclear Regulatory Commission
                            Experts we interviewed also identified a number of limitations of NRC
                            processes for assessing the threats posed by natural hazards to
                            operating nuclear power reactors. Three limitations were identified by
                            more than two experts. First, about half of the experts identified as a
                            limitation that NRC has not required licensees of operating reactors to
                            assess natural hazards using PRA and that licensees generally have not
                            done so. One of these experts noted that while NRC generally has good
                            information on natural hazards, the use of PRA would allow NRC to better
                            quantify the adequacy and uncertainty of that information. Another of
                            these experts stated that deterministic assessments of natural hazards
                            alone can provide a false sense of security with regard to the certainty of
                            the information that has been assessed. Second, several experts
                            identified as an additional limitation of NRC processes for assessing
                            natural hazards that some existing assessments are not as robust or up-
                            to-date as they could be. One of these experts noted that NRC generally
                            does not require licensees of operating reactors to systematically
                            reevaluate their natural hazard assessments, and some experts
                            highlighted external flooding and high-wind hazards in particular as
                            warranting further review. Third, a few experts identified as a limitation
                            that NRC’s processes for assessing natural hazard threats are overly
                            bureaucratic and slow and can lead to overly conservative results. One of
                            those experts noted that NRC’s conservatism can potentially lead to the
                            costly overdesign of nuclear power reactors. Another of these experts
                            stated that NRC processes are bureaucratic and time-consuming and
                            undermine the agency’s ability to identify actions that need to be taken
                            promptly in response to new information.


More Than Half of Experts   More than half of the 15 experts we interviewed suggested expanding the
Suggested Expanded          use of PRA for assessing natural hazards at operating nuclear power
Use of PRA                  reactors as a complement to traditional deterministic assessments, and
                            several experts cited a number of advantages, as well as challenges to
                            doing so. The experts’ suggestion was similar to a lesson learned from
                            the Fukushima Daiichi disaster identified by a team from the International
                            Atomic Energy Agency, which found a need for the nuclear power
                            community to increase efforts to develop PRAs for external events. 44 Of
                            the experts who suggested expanding the use of PRA, more than half



                            44
                             International Atomic Energy Agency, Mission Report: The Great East Japan Earthquake
                            Expert Mission (Vienna, Austria: June 16, 2011).




                            Page 24                                    GAO-12-465 Nuclear Regulatory Commission
noted that such risk assessments should not be the sole basis for
decision making but should be used to complement traditional
deterministic assessments in order to provide a more robust approach to
assessing natural hazards. A few experts noted that NRC has already
moved in this direction by requiring that licensees of new reactors
develop and maintain PRAs that address natural hazards. Some experts
emphasized the importance of NRC better integrating PRA into agency
processes for assessing natural hazards, and others said that such risk
assessments of natural hazards should be comprehensive, periodically
updated, and integrated with licensees’ PRAs of internal events.

The experts who suggested expanding the use of PRA for natural
hazards cited a number of advantages of using it to complement
traditional deterministic assessments, including the following:

•   PRA takes a broader look at hazards than traditional deterministic
    assessment by systematically examining all potential causes of an
    accident for any particular hazard, including events beyond those
    accounted for in a reactor’s original design.

•   PRA considers and quantifies the likelihood of events and can help
    inform regulatory priorities by identifying more significant contributors
    to a reactor’s risk profile.

•   PRA provides a structure for explicitly addressing and presenting
    uncertainty and attempts to account for unknowns.

•   PRA can help identify design vulnerabilities that might otherwise be
    overlooked by relying on traditional deterministic assessments alone.

•   PRA can support improved safety decision making by providing risk
    insights.

Several experts also identified challenges to expanding the use of PRA
for natural hazards, including the following:

•   More than half of the experts we interviewed noted that uncertain
    knowledge about natural hazards, particularly the frequency of large
    hazards, presents a challenge in evaluating those hazards. Some
    experts noted the difficulty of identifying the frequency of large natural
    hazards for use in a PRA given the limited data resulting from the brief
    historical record and rarity of the hazards. One of these experts said
    he believes the uncertainties associated with low-probability, high-



Page 25                                 GAO-12-465 Nuclear Regulatory Commission
                               consequence natural hazards are too large for a PRA to produce an
                               accurate risk estimate, and two other experts said the information
                               generated by a PRA would be useful to inform but not determine
                               decisions.

                         •     About half of the experts said another key challenge is the limited
                               number of experts qualified to develop PRAs for natural hazards. One
                               expert noted the number of practitioners that can do this type of risk
                               assessment is small and that it is important that more people be
                               trained to conduct them. Another expert said that finding people to do
                               these analyses, more so than the cost involved in conducting them,
                               represents the primary challenge to expanding the use of PRA. He
                               further noted that this is even more the case now given the actions
                               NRC and industry are taking in response to the Fukushima Daiichi
                               disaster. In June 2008, we noted a similar challenge to NRC’s efforts
                               to transition to a risk-informed approach to fire protection. 45 At that
                               time, numerous NRC, industry, and academic officials we spoke with
                               expressed concern regarding the limited number of personnel with the
                               necessary skills and training to design, review, and inspect against
                               PRAs. Those officials told us that the shortage of skilled personnel
                               was due in part to an increased demand for individuals with critical
                               skills under NRC’s risk-informed approach. We have reported on this
                               challenge of the limited number of PRA practitioners as far back as
                               1985. 46 NRC and industry officials we interviewed agreed that the
                               limited number of experts qualified in PRA remains a challenge today.

                         •     A few experts identified other challenges to expanding the use of PRA
                               for natural hazards, including the cost of developing those risk
                               assessments, the regulatory hurdles to NRC requiring licensees of
                               operating reactors to use PRA, and the care that must be taken when
                               deciding which natural hazards to include in a PRA and which to
                               screen out of the analysis.



Some Experts Suggested   Some of the 15 experts we interviewed suggested changes to NRC
Other Changes to NRC     processes for assessing the threats posed by natural hazards to
Assessment Processes     operating U.S. nuclear power reactors that were unrelated to expanding



                         45
                             GAO-08-747.
                         46
                             GAO/RCED-85-11.




                         Page 26                                  GAO-12-465 Nuclear Regulatory Commission
the use of PRA. Five such changes were suggested by at least two
experts as follows:

•    Several experts suggested that NRC should have licensees revisit
     their existing natural hazard assessments to incorporate current
     knowledge on natural hazards or ensure that the assumptions used in
     the assessments have not changed. Some of these experts noted that
     the state of knowledge on natural hazards such as earthquakes,
     floods, and high-wind events had changed since licensees completed
     their assessments. More than half of the experts we interviewed said
     the NRC Fukushima Daiichi task force’s recommendations that NRC
     require licensees to reevaluate their seismic and flooding hazards and
     confirm them on a periodic basis in the future were useful, and some
     of those experts suggested that the reevaluation should include all
     natural hazards, as it will, according to NRC officials. 47 One expert
     said it would be better if NRC required licensees to perform a
     comprehensive assessment of natural hazards rather than a
     reevaluation of existing assessments against current requirements. A
     few experts said the reevaluations proposed by the task force would
     be of only limited utility. Two of those experts indicated that resources
     would be better devoted to having licensees enhance their reactors’
     abilities to mitigate natural hazards and to reevaluate natural hazards
     as significant new information becomes available rather than on a set
     periodic basis.

•    A few experts suggested that NRC should examine the criteria that
     licensees use to decide whether to assess a natural hazard or screen
     it out of their assessment. One expert suggested that NRC create a
     special category of assessments to consider low probability, high-
     consequence natural hazards that otherwise might be screened out.

•    Two experts suggested that NRC should devote additional resources
     to researching natural hazards in order to inform agency assessments
     and guidance relating to those hazards.


47
  In October 2011, NRC’s Advisory Committee on Reactor Safeguards recommended that
agency staff consider additional external hazards beyond seismic and flooding hazards as
part of the lessons learned from the Fukushima Daiichi disaster. After we completed our
interviews with experts, the 2012 Consolidated Appropriation Act was enacted with a
provision that, among other things, directed NRC to require licensees to reevaluate the
seismic, tsunami, flooding, and other external hazards at their sites against current
requirements and guidance as expeditiously as possible, and thereafter when appropriate,
as determined by the NRC.




Page 27                                      GAO-12-465 Nuclear Regulatory Commission
              •   Two experts suggested that NRC should do more work to assess how
                  natural hazards might affect sites with multiple reactors. One expert
                  expressed the view that there has not been a systematic enough
                  examination of the potential consequences of a natural hazard that
                  might affect multiple reactors.

              •   Two experts suggested that NRC should consider how potential future
                  changes in natural hazards are addressed in assessments. One
                  expert noted, for example, that climate change could potentially lead
                  to changes in natural hazards over reactors’ operating lives.

              In addition, two experts said that they do not believe NRC needs to make
              changes to its processes for assessing the threats posed by natural
              hazards beyond what NRC is already undertaking in response to the
              Fukushima Daiichi disaster. One expert said that NRC and licensees
              should focus on enhancing reactors’ ability to cope with and respond to
              natural hazards rather than devote those resources to further assessing
              natural hazard threats.


              Operating a nuclear power reactor is never entirely free of risk, but
Conclusions   comprehensive assessments of that risk and various contributing risk
              factors—including natural hazards—can help identify vulnerabilities that
              might otherwise be overlooked. Actions taken to mitigate such risks could
              decrease the chance of an accident that could have serious public health,
              environmental, and economic consequences. NRC documents and most
              experts we spoke with indicate that PRA offers NRC and licensees a
              number of advantages that, as a complement to traditional deterministic
              assessments, can provide a more robust approach to assessing natural
              hazards.

              Because NRC and licensees of operating reactors continue to rely
              primarily on deterministic assessments of natural hazards, they are
              realizing PRA’s advantages to a limited extent. We recognize that NRC
              must undertake a thorough review to require licensees of operating
              reactors to develop and maintain PRAs that address natural hazards. In
              particular, we acknowledge the difficulty that NRC officials anticipate in
              reaching a determination that a PRA requirement is warranted for
              operating reactors under existing regulations. Further, we understand
              there are a limited number of experts qualified to develop PRAs for
              natural hazards, and that there is a cost to developing PRAs. However,
              we also note NRC’s overall endorsement of the use of PRA to enhance
              and extend traditional deterministic assessments, as well as the



              Page 28                                GAO-12-465 Nuclear Regulatory Commission
                     significant advantages cited by the experts we interviewed who
                     suggested expanding the use of PRA for assessing natural hazards at
                     operating nuclear power reactors. Moreover, we note that a team from the
                     International Atomic Energy Agency has identified a need to increase
                     efforts to develop PRAs for external events as a lesson learned from the
                     Fukushima Daiichi disaster. While NRC suggested PRA in the 1990s as
                     one potential option for licensees to use to assess natural hazards, most
                     licensees opted not to do so, and agency officials and industry
                     representatives told us they believe that licensees today have only
                     applied PRA to natural hazards to a limited extent. Given all this, PRAs’
                     potential benefits in the natural hazard context may not be realized
                     without efforts by NRC to promote its use. Without conducting the
                     analyses necessary to determine whether a PRA requirement is
                     warranted for operating reactors, however, NRC does not have a strong
                     basis to judge whether or not such a requirement should be implemented.


                     To improve safety decision making by NRC in carrying out its
Recommendation for   responsibility under the Atomic Energy Act to ensure that the operation of
Executive Action     nuclear power plants is consistent with the common defense and security
                     and public health and safety, we recommend that the NRC
                     Commissioners direct agency staff to conduct and document any needed
                     analyses to determine whether the agency should require licensees of
                     operating reactors to develop and maintain PRAs that address natural
                     hazards.


                     We provided a draft of this report to the NRC Commissioners and the
Agency Comments      Secretaries of Commerce, Defense, and the Interior for their review and
and Our Evaluation   comment. The Secretaries of Commerce, Defense, and the Interior had
                     no comments. NRC provided written comments on April 13, 2012, which
                     are reproduced in appendix VI, and technical comments, which we
                     incorporated into the report as appropriate.

                     NRC agreed with the report recommendation. The agency stated it would
                     conduct and document the analysis recommended by GAO in the context
                     of follow-on actions for related ongoing agency initiatives after sufficient
                     information has been gathered from those activities to better inform the
                     analysis. In addition, NRC asserted that it will continue to evaluate its
                     processes and policies regarding the enhanced use of PRA and risk
                     insights as part of its overall regulatory framework. As we noted in our
                     report, NRC documents and most experts we spoke with indicate that
                     PRA offers NRC and licensees a number of advantages that, as a


                     Page 29                                GAO-12-465 Nuclear Regulatory Commission
complement to traditional deterministic assessments, can provide a more
robust approach to assessing natural hazards. We also noted that
officials we interviewed and data we obtained indicate that NRC and
licensees apply PRA to natural hazards at operating nuclear power
reactors to a limited extent. We continue to believe that until NRC
completes the analysis necessary to determine whether a PRA
requirement is warranted for operating reactors, NRC will not have a
strong basis to judge whether or not such a requirement should be
implemented, and PRAs’ potential benefits in the natural hazard context
may not be realized.


As agreed with your offices, unless you publicly announce the contents of
this report earlier, we plan no further distribution until 30 days from the
report date. At that time, we will send copies to the Chairman of the NRC,
the Secretaries of Commerce, Defense, and the Interior, the appropriate
congressional committees, and other interested parties. In addition, this
report will be available at no charge on the GAO website at
http://www.gao.gov.

If you or your staff members have any questions about this report, please
contact me at (202) 512-3841 or ruscof@gao.gov. Contact points for our
Offices of Congressional Relations and Public Affairs may be found on
the last page of this report. Key contributors to this report are listed in
appendix VII.




Frank Rusco
Director, Natural Resources and Environment




Page 30                                GAO-12-465 Nuclear Regulatory Commission
Appendix I: Objectives, Scope, and
              Appendix I: Objectives, Scope, and
              Methodology



Methodology

              Our review provides information on: (1) the extent to which probabilistic
              risk assessment (PRA) is applied to natural hazards at operating U.S.
              nuclear power reactors and (2) expert views on and suggested changes,
              if any, to Nuclear Regulatory Commission (NRC) processes for assessing
              natural hazards at operating U.S. nuclear power reactors. To address
              both of these objectives, we reviewed relevant literature and NRC
              documents and met with officials from NRC, the nuclear power industry,
              public interest groups, and others to understand NRC processes for
              assessing natural hazards at nuclear power reactors.

              Specifically, to address the first objective, we reviewed relevant
              documents and data obtained from NRC and selected licensees on the
              extent to which PRA has been applied to natural hazards. We interviewed
              knowledgeable officials about the data and found the data to be
              sufficiently reliable for the purposes of our report. We reviewed NRC
              policies and procedures, as well as NRC initiatives related to the
              assessment of natural hazards. We also reviewed the NRC near-term
              task force’s report on insights gained from the Fukushima Daiichi disaster
              and documented the actions taken by NRC on recommendations related
              to the assessment of natural hazards. In addition, we visited a
              nonprobability sample of five nuclear power plants to interview licensees
              about the actions they have taken to assess natural hazards. 1 The five
              nuclear power plants we visited were the Browns Ferry Nuclear Plant in
              Alabama, the Diablo Canyon Power Plant in California, the North Anna
              Power Station in Virginia, the San Onofre Nuclear Generating Station in
              California, and the Turkey Point Nuclear Plant in Florida. We selected
              these sites to capture a variety of characteristics, including reactor and
              containment vessel type, operating license issuance date, license
              renewal status, and natural hazard activity level.

              To address the second objective, we summarized the results of
              semistructured interviews with experts in assessing natural hazards, risks
              to nuclear power reactors, or both. We first reviewed NRC documentation
              about processes used to assess natural hazards at nuclear power
              reactors and confirmed our understanding of those processes with NRC.
              Then, we identified 43 experts from our review of the literature, prior GAO
              reports, congressional and NRC hearings, and recommendations from


              1
                Because this was a nonprobability sample, the information we gathered from these site
              visits is not generalizeable to all 65 operating nuclear power plants but provides important
              illustrative information.




              Page 31                                         GAO-12-465 Nuclear Regulatory Commission
Appendix I: Objectives, Scope, and
Methodology




NRC, the Nuclear Energy Institute, the Union of Concerned Scientists,
and experts in assessing risks to nuclear power reactors. From this list,
we selected 15 experts based on (1) the relevance of their expertise as
reflected in publications, testimonies, and their biographies; (2) the
relevance and extent of their publications; (3) the relevance and extent of
their testimonies before Congress and NRC; and (4) recommendations
from others in the field. Finally, to ensure coverage and a range of
perspectives, we selected experts who came from academia,
government, industry, public interest groups, and other affiliations;
provided perspectives from both those inside NRC or the nuclear power
industry and from those outside of those two groups; and provided
perspectives from those publicly supportive, publicly critical, and those
without a public position on nuclear power. Appendix II lists the experts
we interviewed. We conducted a content analysis to assess experts’
responses to a standard set of questions and grouped responses into
overall themes. The views expressed by experts do not necessarily
represent the views of GAO. Not all of the experts provided their views on
all issues. We did not independently evaluate the quality of NRC
processes for assessing natural hazards and the threats they pose to
nuclear power reactors.

During the course of our review, we interviewed NRC officials from the
Office of General Counsel, Office of New Reactors, Office of Nuclear
Reactor Regulation (including the Japan Lessons Learned Project
Directorate), Office of Nuclear Regulatory Research, and Risk
Management Task Force in headquarters, as well as NRC officials in
Region II and Region IV and the resident inspectors at the five nuclear
power plants we visited. We also interviewed officials and reviewed
documents from the National Oceanic and Atmospheric Administration,
the U.S. Army Corps of Engineers, and the U.S. Geological Survey on the
current state of knowledge on natural hazards, how that knowledge has
changed over time, and the related uncertainty. Further, we interviewed
representatives from American Nuclear Insurers, the Nuclear Energy
Institute, and the Union of Concerned Scientists to discuss their views on
NRC processes for assessing natural hazards and the threats those
hazards pose to nuclear power reactors.

We conducted this performance audit from May 2011 to April 2012 in
accordance with generally accepted government auditing standards.
Those standards require that we plan and perform the audit to obtain
sufficient, appropriate evidence to provide a reasonable basis for our
findings and conclusions based on our audit objectives. We believe that



Page 32                                GAO-12-465 Nuclear Regulatory Commission
Appendix I: Objectives, Scope, and
Methodology




the evidence obtained provides a reasonable basis for our findings and
conclusions based on our audit objectives.




Page 33                              GAO-12-465 Nuclear Regulatory Commission
Appendix II: List of Experts
               Appendix II: List of Experts




               •   Dennis C. Bley, Buttonwood Consulting, Inc., Member of NRC’s
                   Advisory Committee on Reactor Safeguards

               •   Biff Bradley, Nuclear Energy Institute

               •   Robert J. Budnitz, Lawrence Berkeley National Laboratory

               •   Thomas B. Cochran, Natural Resources Defense Council

               •   Karl N. Fleming, KNF Consulting Services LLC

               •   B. John Garrick, U.S. Nuclear Waste Technical Review Board

               •   Michael W. Golay, Massachusetts Institute of Technology

               •   N. Prasad Kadambi, Consultant

               •   William Leith, U.S. Geological Survey

               •   William Levis, PSEG Power LLC

               •   Stuart Lewis, Electric Power Research Institute

               •   David A. Lochbaum, Union of Concerned Scientists

               •   Mohammad Modarres, University of Maryland

               •   Ali Mosleh, University of Maryland

               •   Doug True, ERIN Engineering & Research, Inc.




               Page 34                                  GAO-12-465 Nuclear Regulatory Commission
Appendix III: Key Developments in NRC’s
              Appendix III: Key Developments in NRC’s
              Approach to Probabilistic Risk Assessment



Approach to Probabilistic Risk Assessment

              According to NRC documents, NRC is moving toward a risk-informed,
              performance-based approach to decision making that is being
              implemented in phases. This approach extends the traditional
              deterministic approach in part by incorporating PRA—a systematic
              method for assessing what can go wrong, its likelihood, and its potential
              consequences to determine quantitative estimates of risk. The timeline
              below describes some of the key developments in NRC’s approach to
              PRA, including its application to natural hazards.


1975          NRC publishes the first PRA of nuclear power reactors. 1 According to an
              NRC document, this study marks the first U.S. attempt to systematically
              evaluate a large spectrum of accidents and to use quantitative techniques
              to evaluate severe accident probabilities and off-site radiological
              consequences in an integrated manner to obtain a more realistic estimate
              of public risk. The study challenged the concept that conservative safety
              analysis of design-basis accidents could establish an upper limit of public
              risk.


1979          An accident occurs at the Three Mile Island nuclear power plant, resulting
              in a partial meltdown of a reactor core. According to an NRC document,
              the accident substantiated risk insights generated through the 1975 study
              and led to the increased use of PRA to identify vulnerabilities in the
              nuclear industry.


1986          NRC issues its Safety Goal Policy Statement in which it broadly defines
              an acceptable level of radiological risk that might be imposed on the
              public as a result of nuclear power reactor operations and calls for the
              use of PRA to measure achievement of the agency’s individual and
              societal safety goals. 2




              1
               NRC, Reactor Safety Study: An Assessment of Accident Risks in U.S. Commercial
              Nuclear Power Plants, WASH-1400(NUREG 75/014) (Washington, D.C.: October 1975).
              2
               NRC, Safety Goals for the Operations of Nuclear Power Plants; Policy Statement, 51
              Fed. Reg. 30,028 (Aug. 21, 1986).




              Page 35                                      GAO-12-465 Nuclear Regulatory Commission
       Appendix III: Key Developments in NRC’s
       Approach to Probabilistic Risk Assessment




1988   NRC initiates the Individual Plant Examination program and requests that
       each licensee perform an examination to identify plant-specific
       vulnerabilities to severe accidents that could be fixed with low-cost
       improvements. 3 One of several program objectives is for each licensee to
       gain a more quantitative understanding of the overall probability of core
       damage and radioactive material releases. NRC identifies PRA as one
       acceptable approach for licensees to use in conducting their examination
       but limits the scope of the effort to internal events.


1990   NRC publishes a follow-on study to its original 1975 study that advances
       the state of the art in PRA, particularly the analysis of uncertainty. 4


1991   NRC initiates the Individual Plant Examination of External Events
       program and requests that each licensee identify and report to the agency
       all plant-specific vulnerabilities to severe accidents caused by external
       events, including natural hazards such as seismic events, floods, and
       high-wind events. 5 NRC suggests PRA as one possible method for
       licensees to use in responding to NRC’s request.


1994   NRC develops a PRA implementation plan that aims to ensure PRA is
       implemented in a consistent and predictable manner in regulatory
       activities. 6




       3
        NRC, Individual Plant Examination for Severe Accident Vulnerabilities, 10 CFR 50.54(f),
       Generic Letter No. 88-20 (Washington, D.C.: Nov. 23, 1988).
       4
        NRC, Severe Accident Risks: An Assessment for Five U.S. Nuclear Power Plants,
       NUREG-1150 (Washington, D.C.: December 1990).
       5
        NRC, Individual Plant Examination of External Events for Severe Accident
       Vulnerabilities—10 CFR 50.54(f), Generic Letter No. 88-20, Supplement 4 (Washington,
       D.C.: June 28, 1991).
       6
        NRC, Proposed Agency-Wide Implementation Plan for Probabilistic Risk Assessment,
       SECY-94-219 (Washington, D.C.: Aug. 19, 1994).




       Page 36                                       GAO-12-465 Nuclear Regulatory Commission
       Appendix III: Key Developments in NRC’s
       Approach to Probabilistic Risk Assessment




1995   NRC issues a policy statement regarding the expanded use of PRA. 7 In
       its approval of the policy statement, the NRC stated its expectation that
       “the use of PRA technology should be increased in all regulatory matters
       to the extent supported by state-of-the-art in PRA methods and data and
       in a manner that complements the NRC’s deterministic approach and
       supports the NRC’s traditional defense-in-depth philosophy.”


1996   NRC requires new nuclear power reactors licensed after January 1997 to
       be sited and designed with respect to geological and seismic
       determinations based on an appropriate analysis, such as a probabilistic
       seismic hazard analysis. 8


1998   NRC establishes a structure for risk-informed decision making to improve
       consistency in regulatory decisions where PRA results are used to
       supplement traditional deterministic and defense-in-depth approaches. 9
       The structure consists of five key principles: proposed changes must (1)
       meet current regulations, (2) be consistent with the defense-in-depth
       philosophy, and (3) maintain sufficient safety margins; (4) when proposed
       changes result in an increase in risk, the increases should be small and
       consistent with the intent of NRC’s Safety Goal Policy Statement; and (5)
       the impact of the proposed changes should be monitored using
       performance management strategies. The structure acknowledges that
       assurance of adequate protection of public health and safety
       encompasses more than simply demonstrating an acceptable level of
       overall risk.




       7
        NRC, Use of Probabilistic Risk Assessment Methods in Nuclear Regulatory Activities;
       Final Policy Statement, 60 Fed. Reg. 42,622 (Aug. 16, 1995).
       8
       10 C.F.R. Part 100, subpart B.
       9
        NRC, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions
       on Plant-Specific Changes to the Licensing Basis, Regulatory Guide 1.174 (Washington,
       D.C.: July 1998).




       Page 37                                      GAO-12-465 Nuclear Regulatory Commission
       Appendix III: Key Developments in NRC’s
       Approach to Probabilistic Risk Assessment




2000   NRC develops a strategy 10 for implementing risk-informed regulation in
       response to a GAO recommendation. 11

2007   NRC issues regulations requiring that applicants for combined licenses
       for new nuclear power reactors submit a description and the results of a
       reactor-specific PRA to NRC as part of their license application. 12 NRC
       also requires licensees of new nuclear power reactors that will operate
       their reactors under a combined license to develop by the scheduled date
       of their initial fuel loading a Level 1 and Level 2 reactor-specific PRA that
       covers, among other things, initiating events for which there are NRC-
       endorsed consensus quality standards 1 year prior to the scheduled date
       for initial fuel loading. 13 Licensees are required to maintain their PRA and
       upgrade it every 4 years over the operating life of the reactor, as well as
       when the licensee submits a license renewal application. 14 Also, NRC
       develops its risk-informed and performance-based implementation plan. 15
       The plan provides guidance and direction regarding activities the agency
       undertakes to integrate risk information and performance measures into
       its regulations, regulatory guidance, and oversight processes.


2009   NRC issues a regulatory guide that provides guidance to licensees to use
       in determining the technical adequacy of a PRA for regulatory decision
       making and endorses certain American Society of Mechanical Engineers
       and American Nuclear Society national consensus standards for PRA



       10
        NRC, Risk-Informed Regulation Implementation Plan, SECY-00-0213 (Washington,
       D.C.: Oct. 26, 2000).
       11
         GAO/RCED-99-95. GAO recommended that “the Commissioners of NRC direct the staff
       to develop a comprehensive strategy that includes but is not limited to objectives, goals,
       activities, and time frames for the transition to risk-informed regulation; specifies how the
       Commission expects to define the scope and implementation of risk-informed regulation;
       and identifies the manner in which it expects to continue the free exchange of operational
       information necessary to improve the quality and reliability of risk assessments.”
       12
        10 C.F.R. § 52.79(a)(46).
       13
        10 C.F.R. § 50.71(h)(1).
       14
        10 C.F.R. § 50.71(h)(2), (3).
       15
         NRC, Update on the Improvements to the Risk-Informed Regulation Implementation
       Plan, Enclosure 1 - Risk-Informed and Performance-Based Plan, SECY-07-0074
       (Washington, D.C.: Apr. 26, 2007).




       Page 38                                         GAO-12-465 Nuclear Regulatory Commission
       Appendix III: Key Developments in NRC’s
       Approach to Probabilistic Risk Assessment




       quality. 16 Among other things, those standards address the application of
       PRA to natural hazards. 17


2011   The Chairman of the NRC charters a task force to develop a strategic
       vision and assess options for a more comprehensive and holistic risk-
       informed, performance-based regulatory approach, with one option being
       better incorporating risk management concepts into NRC’s regulatory
       programs. 18 Later that year, in response to the Fukushima Daiichi
       disaster, NRC charters a staff task force to review its processes and
       regulations and to recommend whether NRC should make near-term
       improvements to its regulatory system. 19 The task force makes several
       recommendations in its final report, including requiring that licensees
       reevaluate the seismic and flooding hazards at their sites against current
       NRC guidance and requirements. 20 With policy direction from the NRC,
       the agency staff moves forward with actions to implement the task force
       recommendations. 21




       16
        NRC, An Approach for Determining the Technical Adequacy of Probabilistic Risk
       Assessment Results for Risk-Informed Activities, Regulatory Guide 1.200 (Washington,
       D.C.: March 2009).
       17
         American Society of Mechanical Engineers and American Nuclear Society, Addenda to
       ASME/ANS RA-S-2008: Standard for Level 1/Large Early Release Frequency Probabilistic
       Risk Assessment Results for Nuclear Power Plant Applications, ASME/ANS RA-Sa-2009
       (ASME, New York, NY; ANS, La Grange Park, IL: February 2009).
       18
        NRC, Charter for Task Force for Assessment of Options for More Holistic Risk-Informed,
       Performance-Based Regulatory Approach (Washington, D.C.: Feb. 11, 2011).
       19
         NRC, Charter for the Nuclear Regulatory Commission Task Force to Conduct a Near-
       Term Evaluation of the Need for Agency Actions Following the Events in Japan
       (Washington, D.C.: Mar. 30, 2011).
       20                                                              st
        NRC, Recommendations for Enhancing Reactor Safety in the 21 Century: The Near-
       Term Task Force Review of Insights From the Fukushima Dai-ichi Accident (Washington,
       D.C: July 12, 2011).
       21
         NRC, Prioritization of Recommended Actions to Be Taken in Response to Fukushima
       Lessons Learned, SECY-11-0137 (Washington, D.C.: Oct. 3, 2011).




       Page 39                                      GAO-12-465 Nuclear Regulatory Commission
       Appendix III: Key Developments in NRC’s
       Approach to Probabilistic Risk Assessment




2012   NRC issues three orders and a request for information in response to
       lessons learned from the Fukushima Daiichi disaster. 22 As part of the
       request for information, the staff asks licensees to reevaluate the seismic
       and flooding hazards at their sites and suggests PRA as one possible
       method to address the seismic hazard reevaluation.




       22
         NRC, Staff Requirements—SECY-12-0025—Proposed Orders and Requests for
       Information in Response to Lessons Learned From Japan’s March 11, 2011, Great
       Tohoku Earthquake and Tsunami (Washington, D.C.: Mar. 9, 2012).




       Page 40                                     GAO-12-465 Nuclear Regulatory Commission
Appendix IV: Information on Developing a
              Appendix IV: Information on Developing a
              Probabilistic Risk Assessment



Probabilistic Risk Assessment

              Probabilistic risk assessments are used to evaluate several categories of
              initiating events––that is, events that can lead to a reactor accident—
              including internal events, which start inside the nuclear power plant or the
              electric system serviced by the power plant (e.g., random hardware
              failures and operator actions), and external events, which typically start
              outside the nuclear power plant, such as natural hazards (e.g.,
              earthquakes, external floods, external fires, and high-wind events).
              According to NRC documents, external events are of significant concern
              since they can both initiate core damage accidents and negate or
              compromise the safety systems or procedures used to prevent or mitigate
              such accidents.

              According to NRC documents, PRA can estimate three different levels of
              risk—one focused on reactor core damage, one focused on containment
              release, and one focused on radiological consequences to the public.
              Specifically, Level 1 PRAs evaluate events that can lead to plant
              accidents and examine reactor systems and operators’ responses to
              calculate “core damage frequency”—the frequency of the combinations of
              initiating events, hardware failures, and human errors leading to the
              uncovering of the reactor core such that reflooding of the core is not
              imminent. A Level 1 PRA consists of six major steps: (1) identifying a
              comprehensive list of events that can lead to accidents and grouping
              those events into categories based on their potential impact on accident
              response systems; (2) establishing success criteria based on traditional
              engineering analyses; (3) modeling accident sequences; (4) estimating
              parameters for the analysis such as initiating event frequencies and the
              failure rates of particular components; (5) quantifying accident
              sequences; and (6) documenting and evaluating the results. To
              accomplish these steps, a PRA employs several specific techniques,
              including event trees, fault trees, human reliability analyses, and Monte
              Carlo methods (see table 2). Analysts use these methods to estimate the
              core damage frequency for each accident sequence. Those frequencies
              are then totaled to calculate the total core damage frequency for a
              reactor.




              Page 41                                    GAO-12-465 Nuclear Regulatory Commission
                                         Appendix IV: Information on Developing a
                                         Probabilistic Risk Assessment




Table 2: Selected Techniques Used in PRA

Technique                           Description
Accident sequence analysis (event   Model responses to each event that can initiate an accident. For any given initiating event,
trees)                              there are various accident sequences resulting from whether systems operate properly or fail
                                    and what actions operators take. Some accident sequences will result in a safe recovery, and
                                    some will result in reactor core damage. Event trees graphically represent accident
                                    sequences.
System analysis (fault trees)       Model systems in detail. Many events in an event tree represent a system that is needed to
                                    respond to the initiating event. An analysis is performed for each such event, which is
                                    graphically represented with a fault tree that identifies the combination of failures that cause
                                    the overall system to fail. The fault tree logic is then used to calculate overall failure probability.
Human reliability analysis          Used to evaluate human errors that are important to the outcome of an event. Analysts assess
                                    the probability of a human error in light of factors like training, procedures, and expected
                                    conditions during an event.
Monte Carlo methods                 Used to compute risks. Allows analysts to consider variations in each analysis factor, imperfect
                                    knowledge, as well as many possible ways that factors can interact.
                                         Source: NRC.


                                         Level 2 PRAs start with Level 1 core damage accidents and assess the
                                         frequencies of various categories of containment releases. The results for
                                         operating reactors are typically reported in terms of “large early release
                                         frequency”—the frequency of those accidents leading to significant,
                                         unmitigated releases from the reactor’s containment in a time frame prior
                                         to effective evacuation of the nearby population such that there is a
                                         potential for early health effects. Level 3 PRAs start with Level 2
                                         radiological release accidents and assess the public health
                                         consequences of a radiological release in terms of injury to the public and
                                         damage to the environment. 1




                                         1
                                          Because core damage and large early release estimates are easier to calculate than
                                         public health consequences, the results of Level 1 and Level 2 PRAs are often used as
                                         surrogates for the results of a Level 3 PRA. NRC has plans to perform a new Level 3 PRA
                                         for a single operating power plant that will include assessment of natural hazards and be
                                         completed within 4 years.




                                         Page 42                                            GAO-12-465 Nuclear Regulatory Commission
Appendix V: NRC Actions on Natural Hazard
              Appendix V: NRC Actions on Natural Hazard
              Assessment in Response to the Fukushima
              Daiichi Disaster


Assessment in Response to the Fukushima
Daiichi Disaster
              NRC has taken a number of actions in response to the Fukushima Daiichi
              disaster. The timeline below describes actions that relate to natural
              hazard assessments.


March 2011    A 9.0 magnitude earthquake and subsequent tsunami lead to a prolonged
              loss of alternating current electrical power at several reactors at Japan’s
              Fukushima Daiichi nuclear power plant. As a result of the loss of power,
              plant operators are unable to keep three of the reactors cool, which leads
              to fuel melting, hydrogen explosions, and the release of radioactive
              material into the environment. Among several actions, NRC charters a
              staff task force to review its processes and regulations in light of the
              Fukushima Daiichi disaster and to recommend whether NRC should
              make near-term improvements to its regulatory system. 1


July 2011     The NRC task force issues its final report. 2 The task force finds that NRC
              regulations and guidance provide a robust approach for assessing natural
              hazards but notes that NRC’s processes for assessing natural hazards
              have evolved over time. As a result, the licensing bases, design, and level
              of protection from natural hazards differ among operating reactors
              depending on when the reactors were built and when they were licensed
              for operation. Based on these findings, the task force recommends
              actions to, among other things, clarify and strengthen NRC’s regulatory
              framework for protection against natural hazards. Three of these
              recommended actions relate to the assessment of natural hazards.
              Specifically, the task force recommends that (1) NRC order licensees to
              reevaluate the seismic and flooding hazards at their sites against current
              NRC requirements and guidance and, if necessary, update their reactor
              design bases; (2) NRC initiate rulemaking to require licensees to confirm
              their seismic and flooding hazards every 10 years, address any new and
              significant information and, if necessary, update their reactor design
              bases; and (3) NRC order licensees to check their seismic and flood
              protection features to identify and address any plant-specific


              1
               NRC, Charter for the Nuclear Regulatory Commission Task Force to Conduct a Near-
              Term Evaluation of the Need for Agency Actions Following the Events in Japan
              (Washington, D.C.: Mar. 30, 2011).
              2
               NRC, Recommendations for Enhancing Reactor Safety in the 21st Century: The Near-
              Term Task Force Review of Insights from the Fukushima Dai-ichi Accident (Washington,
              D.C.: July 12, 2011).




              Page 43                                     GAO-12-465 Nuclear Regulatory Commission
                 Appendix V: NRC Actions on Natural Hazard
                 Assessment in Response to the Fukushima
                 Daiichi Disaster




                 vulnerabilities and verify the adequacy of monitoring and maintenance for
                 protection features such as watertight barriers and seals.


August 2011      The NRC directs agency staff, among other things, to engage
                 stakeholders on the task force recommendations and to identify and
                 prioritize the recommendations that in the staff’s view can and should be
                 implemented without unnecessary delay. 3


September 2011   Agency staff report to the NRC Commissioners on the task force
                 recommendations that in their view can and should be implemented
                 without unnecessary delay. 4 Among other things, the staff recommends
                 that the NRC move forward on requiring licensees to reevaluate the
                 seismic and flooding hazards at their sites against current NRC
                 requirements and guidance. The staff also recommends that the NRC
                 move forward on requiring licensees to check their seismic and flood
                 protection features.


October 2011     Agency staff propose a prioritization of the task force recommendations to
                 the NRC Commissioners and describe the actions necessary to
                 implement the recommendations. 5 The staff suggests deferring the task
                 force recommendation that NRC initiate rulemaking to require licensees
                 to confirm their seismic and flooding hazards every 10 years until the
                 related recommendation for licensees to reevaluate seismic and flooding
                 hazards is implemented. Later in the month, the NRC approves the staff’s
                 proposal on the task force recommendations that can and should be
                 implemented without unnecessary delay and says that the agency should




                 3
                  NRC, Staff Requirements—SECY-11-0093—Near-Term Report and Recommendations
                 for Agency Actions Following the Events in Japan (Washington, D.C.: Aug. 19, 2011).
                 4
                  NRC, Recommended Actions to be Taken Without Delay From the Near-Term Task
                 Force Report, SECY-11-0124 (Washington, D.C.: Sept. 9, 2011).
                 5
                  NRC, Prioritization of Recommended Actions to Be Taken in Response to Fukushima
                 Lessons Learned, SECY-11-0137 (Washington, D.C.: Oct. 3, 2011).




                 Page 44                                     GAO-12-465 Nuclear Regulatory Commission
                Appendix V: NRC Actions on Natural Hazard
                Assessment in Response to the Fukushima
                Daiichi Disaster




                strive to complete and implement the lessons learned from the
                Fukushima Daiichi disaster by 2016. 6


December 2011   The NRC approves the agency staff’s proposals on implementing task
                force recommendations and supports actions on several, including the
                recommendations that licensees reevaluate their seismic and flooding
                hazards against current NRC requirements and guidance and check their
                seismic and flood protection features. 7 Later in the month, Congress
                passes and the President signs the 2012 Consolidated Appropriations
                Act, which includes a provision directing NRC to require that licensees
                reevaluate external hazards at their sites, including seismic and flooding
                hazards, as expeditiously as possible. 8


January 2012    NRC announces that it is accelerating its plans for implementing the task
                force recommendations. According to NRC officials, agency staff will
                propose expanding licensee reevaluations beyond seismic and flooding
                hazards to include all natural hazards that are relevant to a site, but they
                expect to recommend that the reevaluation of seismic and flooding
                hazards take priority over other natural hazards.


February 2012   The NRC staff proposes issuing three orders and a request for
                information in response to lessons learned from the Fukushima Daiichi
                disaster. 9 The staff’s stated goal is for the orders and request for
                information to be issued before the first anniversary of the earthquake
                and tsunami that led to the Fukushima Daiichi disaster. As part of the
                proposed request for information, the staff plans to ask licensees to



                6
                NRC, Staff Requirements—SECY-11-0124—Recommended Actions to be Taken
                Without Delay From the Near-Term Task Force Report (Washington, D.C.: Oct. 18, 2011).
                7
                 NRC, Staff Requirements—SECY-11-0137—Prioritization of Recommended Actions to
                Be Taken in Response to Fukushima Lessons Learned (Washington, D.C.: Dec. 15,
                2011).
                8
                 Consolidated Appropriations Act, 2012, Pub. L. No. 112-74, Div. B, § 402 (Dec. 23,
                2011).
                9
                 NRC, Proposed Orders and Requests for Information in Response to Lessons Learned
                from Japan’s March 11, 2011, Great Tohoku Earthquake and Tsunami, SECY-12-0025
                (Washington, D.C.: Feb. 17, 2012).




                Page 45                                       GAO-12-465 Nuclear Regulatory Commission
             Appendix V: NRC Actions on Natural Hazard
             Assessment in Response to the Fukushima
             Daiichi Disaster




             reevaluate the seismic and flooding hazards at their sites. NRC staff
             propose addressing other natural hazards, such as wind and missile
             loads from tornados and hurricanes, at a later date once sufficient
             resources are available for the reevaluations. The staff also plans to ask
             licensees to check their seismic and flood protection features.


March 2012   NRC issues the three orders and the request for information proposed by
             agency staff in February. 10




             10
               NRC, Staff Requirements—SECY-12-0025—Proposed Orders and Requests for
             Information in Response to Lessons Learned From Japan’s March 11, 2011, Great
             Tohoku Earthquake and Tsunami (Washington, D.C.: Mar. 9, 2012).




             Page 46                                     GAO-12-465 Nuclear Regulatory Commission
Appendix VI: Comments from the Nuclear
             Appendix VI: Comments from the Nuclear
             Regulatory Commission



Regulatory Commission




             Page 47                                  GAO-12-465 Nuclear Regulatory Commission
Appendix VI: Comments from the Nuclear
Regulatory Commission




Page 48                                  GAO-12-465 Nuclear Regulatory Commission
Appendix VII: GAO Contact and Staff
                  Appendix VII: GAO Contact and Staff
                  Acknowledgments



Acknowledgments

                  Frank Rusco, (202) 512-3841, or ruscof@gao.gov
GAO Contact
                  In addition to the individual named above, Kimberly Gianopoulos,
Staff             Assistant Director; David Marroni; Emmy Rhine; and Ashley Vaughan
Acknowledgments   made key contributions to this report. Important contributions were also
                  made by R. Scott Fletcher, Cindy Gilbert, Jonathan Kucskar, Alison
                  O’Neill, Timothy Persons, Kiki Theodoropoulos, and Jack Wang.




(361295)
                  Page 49                               GAO-12-465 Nuclear Regulatory Commission
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