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Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2 (2016)

Chapter: 4 Reevaluation of Findings and Recommendations from Previous NAS Reports

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Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
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4

Reevaluation of Findings and Recommendations from Previous NAS Reports

The focus of this chapter is on the second charge of the study task (Sidebar 1.2 in Chapter 1), which calls for a

“Reevaluation of the conclusions from previous NAS studies on safety and security of spent nuclear fuel and high-level radioactive waste storage, particularly with respect to the safety and security of current storage arrangements and alternative arrangements in which the amount of commercial spent fuel stored in pools is reduced.”

The “previous NAS studies” referred to in this task is a single study carried out in 2003-2004 at the request of the U.S. Congress. That study addressed the four tasks shown in Sidebar 4.1 and produced two reports:

  • A report containing classified and other security-related information,1 hereafter referred to as the classified report (NRC, 2004), and
  • An abbreviated version of this classified report that was suitable for unrestricted public release, hereafter referred to as the public report (NRC, 20062).

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1 That is, Safeguards Information, which is protected from unauthorized disclosure under Section 147 of the Atomic Energy Act, as well as sensitive unclassified non-safeguards information, referred to by many federal agencies as “official use only” information, which is restricted from public release through the Freedom of Information Act.

2 Completion and release of the public report was delayed because of an extended security review by the sponsoring agency (U.S. Nuclear Regulatory Commission).

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
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The public report is similar in content to the classified report and contains all of its findings and recommendations. However, redactions and wording modifications were made to the classified report, including its findings and recommendations, to remove classified and other security-related information.

The discussions in this chapter are referenced primarily to the public report (NRC, 2006). Where necessary for completeness, identification of classified and other security-related information in the classified report (NRC, 2004) is made by reference to specific sections and page numbers in that report.

Table 4.13 summarizes the committee’s reevaluation of the findings and recommendations in the public report (NRC, 2006). The left-hand column of the table displays the findings and recommendations in the public report (NRC, 2006) organized by their order of presentation in that report. The committee’s reevaluation is presented in the right-hand column of the table, also in the form of findings and recommendations. To avoid confusion, these findings and recommendations are numbered using a scheme different from those in the National Research Council public report (NRC, 2006).4

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3 The table appears on pp. 102-110 at the end of this chapter because of its length.

4 The findings and recommendations in NRC (2006) are numbered using the format xy, where x corresponds to the task number in NRC (2006) (i.e., tasks 1-4) and y is a serial letter (i.e., A-E). In the present report, the findings and recommendations are numbered using the format 4.z, where z is a serial number (1, 2, . . . ).

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

In performing its reevaluation, the present committee paid particular attention to the disposition of recommendations in the public report (NRC, 2006) by the U.S. Nuclear Regulatory Commission (USNRC) and the nuclear industry. The committee gathered information from the USNRC, nuclear industry, and independent analysts (see Appendix B) to determine (1) whether and how these recommendations were addressed and (2) what additional actions, if any, are needed.

The following sections provide a discussion of the committee’s reevaluations. The sections are organized identically to those in Table 4.1. Detailed supporting information for some of the present committee’s findings and recommendations in this chapter is provided in Appendix A and Chapters 5-7.

4.1 TERRORIST ATTACKS ON SPENT FUEL STORAGE OR THEFT OF SPENT FUEL

Chapter 2 of NRC (2006) addresses the fourth study task in Sidebar 4.1:

“Explicitly consider the risks of terrorist attacks on [spent fuel] and the risk these materials might be used to construct a radiological dispersal device.”5

The chapter provides background information on risk assessment and a brief discussion of possible terrorist motivations for attacking a nuclear plant and its spent fuel storage facilities. The report concluded that the terrorist attack risks could not be addressed “using quantitative and comparative risk assessments.” Instead, the report examined “a range of possible terrorist attack scenarios in terms of (1) their potential for damaging spent fuel pools and dry storage casks; and (2) their potential for radioactive material releases” (NRC, 2006, p. 27). The report provided three findings and three recommendations to address the fourth study task (see Table 4.1):

  • Finding 2A (NRC, 2006) notes that the probability of terrorist attacks on spent fuel storage could not be assessed quantitatively or comparatively and that spent fuel storage facilities could not be dismissed as targets for such attacks.
  • Finding 2B (NRC, 2006) notes that the likelihood that terrorists could steal enough spent fuel for use in a significant radiological dispersal device is small. Recommendation 2B (NRC, 2006) encouraged the USNRC to review and upgrade, where necessary, its requirements for protecting spent fuel rods not contained in fuel

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5 That is, a device that disperses radioactive material using explosives or other means.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
  • assemblies from knowledgeable insiders,6 especially in facilities where fuel rods or portions of rods are being stored in pools.

  • Finding 2C (NRC, 2006) notes that a number of security improvements at nuclear plants have been instituted since the events of September 11, 2001, but that the USNRC did not provide enough information to evaluate the effectiveness of these procedures for protecting stored spent fuel. Recommendation 2C (NRC, 2006) encouraged the performance of an independent7 assessment of surveillance and security measures for protecting stored spent fuel.

The committee’s reevaluation of these findings and recommendations is provided in the following sections.

4.1.1 Reevaluation of Finding 2A from NRC (2006)

The present committee agrees with NRC (2006) that there are technical challenges associated with identifying terrorist attack scenarios and quantifying their likelihoods. However, the committee judges that the NRC (2006) report’s focus on quantification challenges is too narrow a perspective for judging the usefulness of applying risk assessment methods to nuclear plant security. The present committee finds (see Finding 4.1 in Table 4.1) that the understanding of security risks at nuclear power plants and spent fuel storage facilities can be improved through risk assessment. Assessments that focus on the risk triplet—scenarios, likelihoods, and consequences—can contribute useful security insights for improving the protection of facilities and operations. Chapter 5 provides the committee’s detailed rationale for this finding.

The present committee received a briefing from USNRC staff on ongoing and planned future work by the agency and the nuclear industry on development and application of risk assessment to nuclear plant security. The committee was encouraged to learn that the agency is working on this issue. The committee also recognizes that support from USNRC management and from the nuclear industry will be essential to the success of this effort. To encourage further progress, the present committee recommends (Recommendation 4.1A) that the U.S. nuclear industry and the USNRC strengthen their capabilities for identifying, evaluating, and managing the risks from terrorist attacks. The committee also recommends (Recommendation 4.1B) that the USNRC sponsor a spent fuel storage security risk assessment of sufficient scope and depth to explore the benefits of this

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6 An insider is a person who is authorized to have physical and/or cyber access to nuclear plant facilities and systems and is working alone or with others to attack the plant.

7 That is, independent of the USNRC and the nuclear industry.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

methodology for enhancing security at U.S. nuclear plants. This assessment should be subjected to independent review by technical peers (i.e., peer review) as part of the development process. See Section 5.1.1.8 in Chapter 5 of the committee’s phase 1 report (NRC, 2014) for a discussion of peer review.

4.1.2 Reevaluation of Finding and Recommendation 2B from NRC (2006)

The committee agrees with Finding 2B in NRC (2006) that the “likelihood terrorists could steal enough spent fuel for use in a radiological dispersal device is small” for the same reasons described in pp. 33-34 of that report. The committee finds (Finding 4.2) that the USNRC has made good progress in upgrading its requirements for protecting spent fuel rods not contained in assemblies: The USNRC has taken steps to improve inventory recordkeeping and controls, enhance inspections, and update regulatory guidance for control and accounting of spent fuel rods and rod fragments. Additionally, the USNRC is undertaking a rulemaking to clarify and strengthen material control and accounting requirements for these materials.

4.1.3 Reevaluation of Finding and Recommendation 2C from NRC (2006)

The committee finds (Finding 4.3) that the USNRC has not obtained the independent examination of surveillance and security measures for protecting stored spent fuel that was recommended by NRC (2006). USNRC staff told the committee that the agency obtains independent reviews of security readiness at nuclear plants through its force-on-force testing program, and also that the agency receives independent advice from the Advisory Committee on Reactor Safeguards8 (ACRS). The committee agrees that the force-on-force testing program is important for assessing the training and operational readiness of a plant’s security forces. However, this testing does not in itself constitute the independent assessment of a plant’s surveillance and security measures recommended by NRC (2006). Moreover, the ACRS does not review USNRC security matters.

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8 The ACRS has oversight on all safety aspects of nuclear plants including spent fuel storage facilities. A recent example of such oversight is the July 18, 2013, ACRS letter report concerning the USNRC’s Spent Fuel Study (see ACRS, 2013). Committee member Michael Corradini is a member of the ACRS. Additional information about the ACRS can be found at http://www.nrc.gov/about-nrc/regulatory/advisory/acrs.html.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

Commission staff provided the present committee with written information9 and briefings on many of the agency’s security requirements and programs, including

  • Physical security at nuclear plants,
  • Security performance characteristics and training,
  • Personnel access authorization at nuclear plants,
  • Design-basis threat for commercial power reactors,
  • Mitigation of the insider threat at commercial power reactors, and
  • Material control and accounting of spent fuel assemblies and fuel rods.

It was clear from these briefings that the USNRC has an extensive set of requirements and programs for ensuring the protection of nuclear plants and their spent fuel storage facilities. However, the present committee was unable to assess the effectiveness of these requirements and programs: Such an assessment was not within the scope of the present study and, moreover, it would require a dedicated effort with a committee having more focused physical, cyber, and personnel security expertise than exists on the present committee.

If the USNRC carries out the independent examination of surveillance and security measures that was recommended by NRC (2006), then the present committee recommends (Recommendation 4.3) that it include an examination of the effectiveness of measures for addressing the insider threat. Several programs have been put into place by the USNRC and the nuclear industry to address the trustworthiness and reliability of individuals with access to nuclear plants to minimize the potential for malevolent actions, including

  • Fitness for duty,
  • Access authorization, and
  • Behavior observation.

The committee received written documents10 and briefings on these measures from USNRC staff.

The USNRC requires licensees to implement an Insider Mitigation Program to oversee and monitor the initial and continuing trustworthiness and reliability of individuals having unescorted access in protected or vital

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9 The written documents contain information that is exempt from public release through the Freedom of Information Act. Consequently, their content cannot be described in this report.

10 The written documents contain Safeguards Information and other security-related information, so their content cannot be described in this report.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

areas of nuclear plants. There is a long-standing assumption by the USNRC that this program reduces the likelihood of an active insider (GAO, 2006). USNRC staff was not able to provide an explanation that was adequate to the committee on how it assesses the effectiveness of these measures for mitigating the insider threat. Moreover, to the committee’s knowledge, there are no programs in place at the USNRC to specifically evaluate the effectiveness of these measures for mitigating the insider threat.

4.2 SAFETY AND SECURITY OF POOL STORAGE

Chapter 3 of NRC (2006) addresses the first task of that study (Sidebar 4.1), which calls for an assessment of the

“Potential safety and security risks of spent nuclear fuel presently stored in cooling pools at commercial reactor sites.”

The safe storage of spent fuel in pools depends critically on keeping the fuel covered with water. This fact was understood more than 40 years ago and was powerfully reinforced by the Fukushima Daiichi accident. If pool water is lost through an accident or terrorist attack (such occurrences are referred to as loss-of-pool-coolant events), then the fuel can become uncovered, possibly leading to fuel damage, including zirconium cladding fires,11 that can result in the release of radioactive materials to the environment. NRC (2006) reviewed work carried out by the USNRC and others to better understand how stored fuel can become uncovered as well as the consequences of such uncovery.

Chapter 3 of NRC (2006) provides background information on spent fuel pool storage, examines potential initiating mechanisms for loss-of-pool-coolant events, and examines the potential consequences of such events. The chapter contains five findings and three recommendations (see Table 4.1):

  • Finding 3A (NRC, 2006) notes that pool storage is required at all operating commercial nuclear plants to cool newly discharged spent fuel.
  • Finding 3B (NRC, 2006) notes that a terrorist attack that partially or completely drained a spent fuel pool could, under some conditions, lead to a propagating zirconium cladding fire and the release of large quantities of radioactive materials to the environment.

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11 The term zirconium cladding fire is used to describe the self-sustaining oxidation of zirconium fuel cladding. This oxidation results in a temperature runaway that can generate enough heat to melt the fuel pellets. See Sidebar 2.2 in Chapter 2.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
  • Finding 3C (NRC, 2006) notes that it appears to be feasible to reduce the likelihood of zirconium cladding fires following a loss-of-pool-coolant event using readily implemented measures.
  • Finding 3D (NRC, 2006) notes that the vulnerabilities of spent fuel pools to terrorist attacks are plant-design specific and can be understood only by examining the characteristics of spent fuel storage at each plant.
  • Finding 3E (NRC, 2006) notes that progress has been made by the USNRC and others to understand the potential vulnerabilities and consequences of terrorist attacks on spent fuel pools but that additional work is needed.
  • Recommendations 3E-1 (NRC, 2006) specifies the additional analyses that should be carried out by the USNRC to improve the understanding of vulnerabilities and consequences of terrorist attacks on pool storage.
  • Recommendation 3E-2 (NRC, 2006) specifies two measures that should be taken by the USNRC to reduce the consequences of loss-of-coolant events.

Finding 3A and Finding 3D of NRC (2006) are statements of fact that require no reevaluation. Consequently, they are not discussed further. The other findings and recommendations are reevaluated in the followings sections.

4.2.1 Reevaluation of Finding 3B from NRC (2006)

NRC (2006) considered four general types of terrorist attack scenarios:

  • Air attacks using large civilian aircraft or smaller aircraft laden with explosives,
  • Ground attacks by groups of well-armed and well-trained individuals,
  • Attacks involving combined air and land assaults, and
  • Thefts of spent fuel for use by terrorists (including knowledgeable insiders) in radiological dispersal devices.

The report noted that

“. . . only attacks that involve the application of large energy impulses or that allow terrorists to gain interior access have any chance of releasing substantial quantities of radioactive material. This further restricts the scenarios that need to be considered. For example, attacks using rocket-propelled grenades (RPGs) of the type that have been carried out in Iraq against U.S. and coalition forces would not likely be successful if the intent

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

of the attack is to cause substantial damage to the facility. Of course, such an attack would get the public’s attention and might even have economic consequences for the attacked plant and possibly the entire commercial nuclear power industry.” (NRC, 2006, p. 30)

The concluding sentence speaks to terrorist intent and metrics for success. That is, if the intent of a terrorist attack is to instill fear into the population and cause economic disruption, then an attack need not result in any release of radioactive material from the plant to be judged a success. The classified report (NRC, 2004) identified particular terrorist attack scenarios that were judged by its authoring committee to have the potential to damage spent fuel pools and result in the loss of water coolant (see Section 2.2 in NRC, 2004). The present committee asked USNRC staff whether any of these attack scenarios had been examined further since NRC (2004) was issued. Staff was unable to present the committee with any additional technical analyses of these scenarios. Consequently, the present committee finds (Finding 4.4) that the USNRC has not undertaken additional analyses of terrorist attack scenarios to provide a sufficient technical basis for a reevaluation of Finding 3B in NRC (2004).

The present committee did not have enough information to evaluate the particular terrorist attack scenarios identified in NRC (2004) and therefore cannot judge their potential for causing damage to spent fuel pools. The committee notes, however, that new remote-guided aircraft technologies have come into widespread use in the civilian and military sectors since NRC (2004) was issued. These technologies could potentially be employed in the attack scenarios described in NRC (2004).

Other types of threats, particularly insider and cyber threats, have grown in prominence since NRC (2004) was issued. There is a need to more fully explore these threats to understand their potential impacts on nuclear plants. The committee-recommended risk assessment (see Finding 4.1 and associated Recommendations 4.1A and 4.1B in Table 4.1) would be an appropriate way to explore these threats.

4.2.2 Reevaluation of Finding 3C from NRC (2006)

NRC (2006) identified three measures that appear to have particular merit for reducing the likelihood of zirconium cladding fires following loss-of-pool-coolant events:

  1. Reconfiguring spent fuel in the pools (i.e., redistribution of high-decay-heat assemblies so that they are surrounded by low-decay-heat assemblies) to more evenly distribute decay-heat loads and enhance radiative heat transfer;
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
  1. Limiting the frequency of offloads of full reactor cores into spent fuel pools, requiring longer shutdowns of the reactor before any fuel is offloaded, and providing enhanced security when such offloads must be made; and
  2. Developing redundant and diverse response systems to mitigate loss-of-pool-coolant events that would be capable of operation even if the pool or overlying building were severely damaged.

The present committee received briefings and technical reports from USNRC and Sandia National Laboratories staff on additional technical analyses and physical experiments that have been carried out since NRC (2004) was released. Some of the key reports examined by the committee are described in Chapter 6. The committee finds (Finding 4.5) that these analyses confirm that reconfiguring spent fuel in pools to more evenly distribute heat loads and enhance heat transfer can be an effective strategy for reducing the likelihood of fuel damage and zirconium cladding fires following loss-of-pool-coolant events. If a loss-of-pool-coolant event results in fuel uncovery, then reconfiguration may provide additional time for mitigating actions to be taken. However, reconfiguring spent fuel in pools does not completely eliminate the risks of zirconium cladding fires, particularly during certain periods following reactor shutdowns and for certain fuel and water configurations in the pool.12 Additional discussion of these issues is provided in Chapter 6.

4.2.3 Reevaluation of Finding 3E and Recommendations 3E-1 and 3E-2 from NRC (2006)

The USNRC and its technical contractor, Sandia National Laboratories, have performed physical experiments and computer analyses (the latter using the Methods for Estimation of Leakages and Consequences of Releases [MELCOR] code; see Sidebar 6.1 in Chapter 6) to elucidate the phenomenology and consequences of loss-of-coolant events in spent fuel pools. These experiments and analyses focused on determining whether runaway oxidation of the fuel cladding (i.e., zirconium cladding fires) could develop in the stored fuel assemblies and propagate to other assemblies in the pool; whether specific configurations of fuel in the pool could delay or prevent this oxidation reaction from occurring; and whether certain mitigating strategies are effective for preventing this reaction from occurring. A description of these studies and some key results and remaining questions are provided in Chapter 6.

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12 Specific shutdown times and fuel and pool water configurations are considered by the USNRC to be security-related information and therefore are not disclosed in this report.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

The present committee finds (Finding 4.6) that these additional experiments and analysis have substantially improved the state of knowledge concerning spent fuel behavior following partial or complete loss of pool water. The committee recommends (Recommendation 4.6) that the USNRC sponsor an end-to-end validation13 of the MELCOR code for modeling loss of coolant in spent fuel pools and validate key submodels. The committee also finds (Finding 4.7) that the USNRC has not analyzed the potential vulnerabilities of spent fuel pools to the specific terrorist attack scenarios identified in NRC (2004) (see Section 4.2.1 in this chapter).

The committee finds (Finding 4.8) that the USNRC and the nuclear industry have made good progress in implementing the actions in Recommendation 3E-1 in NRC (2006). The committee recommends (Recommendation 4.8) that the USNRC and industry take additional steps to further reduce risks of zirconium cladding fires and improve mitigation capabilities. Additional discussion of these issues is provided in Chapter 6.

4.3 SAFETY AND SECURITY OF DRY CASK STORAGE AND COMPARISON WITH POOL STORAGE

Chapter 4 of NRC (2006) addresses the first study task in that report (Sidebar 4.1), which calls for an assessment of the

“Safety and security advantages, if any, of dry cask storage versus wet pool storage at [commercial] reactor sites.”

The chapter provides background information on dry cask storage, its potential risks, as well as potential advantages over pool storage. The chapter contains five findings and one recommendation (see Table 4.1):

  • Finding 4A (NRC, 2006) notes that although there are differences in the robustness of different dry cask designs, the differences are not large.
  • Finding 4B (NRC, 2006) notes that additional steps can be taken to make dry casks less vulnerable to terrorist attacks. Recommen

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13 That is, the validation of key parameters in all phases of an analyzed scenario. For example, for a scenario involving indefinite loss of cooling in a spent fuel pool, the parameters validated would include heat-up rate of the pool; time to equilibrium temperature and variation of equilibrium temperature with time, especially after the two-phase mixture level drops below the top of fuel racks; temperature, pressure, and humidity in the environment above the pool; time at which liquid level drops below the fuel racks; time at which air–water vapor convective flow begins through fuel assemblies; heat-up rate of fuel rods; cladding failure location and size and melt relocation; and, if possible, radioactive material releases from the damaged fuel and their retention in the reactor building.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
  • dation 4B (NRC, 2006) encourages the USNRC to upgrade the requirements of its spent fuel storage regulations to improve the resistance of dry casks to terrorist attacks.

  • Finding 4C (NRC, 2006) notes that dry cask storage does not eliminate the need for pool storage at operating commercial reactors.
  • Finding 4D (NRC, 2006) notes that dry cask storage for older, cooler spent fuel has inherent advantages over pool storage.
  • Finding 4E (NRC, 2006) notes that the USNRC might determine that earlier-than-planned movements of spent fuel from pools into dry cask storage would be prudent to reduce the potential consequences of terrorist attacks on pools at some commercial nuclear plants, depending on the outcome of the analyses recommended in NRC (2004).

Findings 4C and 4D in NRC (2006) are statements of fact that require no reevaluation. Consequently, they are not discussed further. The other findings and recommendations are reevaluated in the followings sections.

4.3.1 Reevaluation of Finding 4A from NRC (2006)

Additional work is now being carried out by the USNRC to understand the robustness of dry casks to terrorist attacks. A general description of this work is given in a March 29, 2012, memo to the director of the USNRC’s Office of Regulatory Research14 and is to include physical testing as well as analysis and evaluation of existing studies. The present committee received a classified briefing on this work. These studies are addressing a range of attack scenarios and appear to be well conceived. However, because this work is still under way, the committee finds (Finding 4.9) that it is unable to assess the work’s technical soundness and completeness.

4.3.2 Reevaluation of Finding and Recommendation 4B from NRC (2006)

The USNRC is incorporating the result of its analysis on dry cask vulnerabilities into its regulations through rulemaking. The rulemaking was still in progress15 when the present study was being completed; consequently, the committee finds (Finding 4.10) that it is unable to evaluate its technical soundness and completeness. The committee recommends (Recommendation 4.10) that the USNRC should give high priority to com-

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14 Available at http://pbadupws.nrc.gov/docs/ML1203/ML120380260.pdf.

15 On October 6, 2015, the Commission approved a 5-year delay in the commencement of this rulemaking. See http://pbadupws.nrc.gov/docs/ML1528/ML15280A105.pdf.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

pleting these analyses and rulemaking. Additional information is provided in Appendix 4A.

4.3.3 Reevaluation of Finding 4E from NRC (2006)

The USNRC has completed technical and regulatory studies (USNRC, 2013, 2014a) to inform a regulatory decision on the need for earlier-than-planned movements (i.e., expedited transfer) of spent fuel at commercial nuclear plants from pools to dry cask storage. The technical study examined the consequences of a large earthquake on a spent fuel pool at a particular nuclear plant. Sensitivity analyses were performed to generalize the results of this study to spent fuel pools at other U.S. nuclear plants. The regulatory study included a safety goal screening and cost-benefit analysis to assess the benefit of expedited transfer of spent fuel from pools to dry casks. These USNRC analyses are described in more detail in Chapter 7 of this report.

The present committee finds (Finding 4.11) that this analysis did not consider spent fuel storage sabotage risks, dry cask storage risks, or certain health consequences that would likely result from a severe nuclear accident. The analysis also used simplifying bounding assumptions that make it technically difficult to assign confidence intervals to the consequence estimates or make valid risk comparisons. A risk assessment that evaluates the three questions of the risk triplet (see Chapter 5) and that accounts for uncertainties in both probability and consequence estimates is needed to address Finding 4E in NRC (2006) to determine whether “earlier movements of spent fuel from pools into dry cask storage would be prudent to reduce the potential consequences of terrorist attacks on pools at some commercial nuclear plants.” The committee recommends (Recommendation 4.11) that the USNRC should perform a spent fuel storage risk assessment to elucidate the risks and potential benefits of expedited transfer of spent fuel from pools to dry casks. Chapter 7 provides the committee’s analysis to support these findings and recommendations.

4.4 IMPLEMENTATION ISSUES

Chapter 5 of NRC (2006) provides a discussion of potential impediments to implementing the recommendations in that report. The impediments involve the timely completion of the expert analyses and ensuring that the results of those analyses are communicated to the nuclear industry so that appropriate and timely mitigating actions can be taken. The chapter contains one finding and recommendation (see Table 4.1).

Finding 5A (NRC, 2006) notes that security restrictions on the sharing of information and analyses is hindering progress in addressing potential vulnerabilities of spent fuel storage to terrorist attacks. Recommenda-

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

tion 5A (NRC, 2006) encourages the USNRC to improve its sharing of information on the vulnerability and consequence studies with nuclear plant operators and dry cask storage vendors on a timely basis.

The present committee received briefings from USNRC staff and the Nuclear Energy Institute (NEI), which represents nuclear plant operators and dry cask storage vendors, on current practices for sharing security-related information. The committee finds (Finding 4.12) that the USNRC has made a commendable effort to improve the sharing of pertinent information on vulnerability and consequence analyses of spent fuel storage with nuclear power plant operators and dry cask storage system vendors. The Commission has sponsored key staff at these organizations for national security clearances, regularly shares important security-related information and threat-related intelligence16 with industry groups, and is responsive to industry requests for information. An NEI representative informed the committee that the industry is satisfied with the content and timeliness of security-related information that it is receiving from the Commission.

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16 The USNRC receives intelligence information from other government agencies on a regular basis. This information is used to assess the threat environment and develop appropriate notifications to plant licensees.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

TABLE 4.1 Committee Reevaluation of Findings and Recommendations from NRC (2006)

Findings and recommendations from NRC (2006) Present committee’s reevaluation of findings and recommendations in NRC (2006)
Terrorist Attacks on Spent Fuel Storage or Theft of Spent Fuel
FINDING 2A: The probability of terrorist attacks on spent fuel storage cannot be assessed quantitatively or comparatively. Spent fuel storage facilities cannot be dismissed as targets for such attacks because it is not possible to predict the behavior and motivations of terrorists, and because of the attractiveness of spent fuel as a terrorist target given the well-known public dread of radiation. FINDING 4.1: The understanding of security risks at nuclear power plants and spent fuel storage facilities can be improved through risk assessment. Event trees and other representational formalisms can be used to systematically explore terrorist attack scenarios, responses, and potential consequences. Expert elicitation can be used to rank scenarios; develop likelihood estimates; and characterize adaptive adversary responses to various preventive, protective, or deterrence actions. The identification of scenarios may be incomplete, and the estimates developed through expert elicitation are subjective and can have large uncertainties. Nevertheless, risk assessment methods that focus on the risk triplet—scenarios, likelihoods, and consequences—can contribute useful security insights.
RECOMMENDATION 4.1A: The U.S. nuclear industry and the U.S. Nuclear Regulatory Commission should strengthen their capabilities for identifying, evaluating, and managing the risks from terrorist attacks. Particular attention is needed to broaden scenario identification, including asymmetric attacks; account for the adaptive nature of adversaries; account for the performance of plant security personnel in responding to the identified scenarios; estimate the potential onsite and offsite consequences of attack scenarios, including radioactive releases and psychological impacts; and develop strategies for countering the identified threats.
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
Findings and recommendations from NRC (2006) Present committee’s reevaluation of findings and recommendations in NRC (2006)
RECOMMENDATION 4.1B: The U.S. Nuclear Regulatory Commission should sponsor a spent fuel storage (wet and dry storage) security risk assessment for U.S. nuclear plants. The primary objectives of this assessment should be to (1) develop and exercise the appropriate methodologies for characterizing risk and estimating uncertainties, and (2) explore the benefits of risk assessment for enhancing security at U.S. nuclear plants. This assessment should be subjected to independent review by technical peers (i.e., peer review) as part of the development process.
FINDING 2B: The committee judges that the likelihood terrorists could steal enough spent fuel for use in a significant radiological dispersal device is small. FINDING 4.2: The U.S. Nuclear Regulatory Commission has made good progress in upgrading its requirements for protecting spent fuel rods not contained in assemblies. The Commission has taken actions to improve inventory controls, enhance inspections, and update regulatory guidance for control and accounting of spent fuel rods and rod fragments. The Commission is also undertaking a rulemaking to clarify and strengthen material control and accounting requirements for these materials.
RECOMMENDATION (2B): The Nuclear Regulatory Commission should review and upgrade, where necessary, its security requirements for protecting spent fuel rods not contained in fuel assemblies from theft by knowledgeable insiders, especially in facilities where individual fuel rods or portions of rods are being stored in pools.
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
Findings and recommendations from NRC (2006) Present committee’s reevaluation of findings and recommendations in NRC (2006)
FINDING 2C: A number of security improvements at nuclear power plants have been instituted since the events of September 11, 2001. The Nuclear Regulatory Commission did not provide the committee with enough information to evaluate the effectiveness of these procedures for protecting stored spent fuel. FINDING 4.3: The U.S. Nuclear Regulatory Commission has not carried out an independent examination of surveillance and security measures for protecting stored spent fuel that was recommended by NRC (2006).
RECOMMENDATION 4.3: The independent examination of surveillance and security measures for protecting stored spent fuel recommended by NRC (2006) should include an examination of the effectiveness of the U.S. Nuclear Regulatory Commission’s programs for mitigating insider threats.
RECOMMENDATION (2C): Although the committee did not specifically investigate the effectiveness and adequacy of improved surveillance and security measures for protecting stored spent fuel, an assessment of current measures should be performed by an independent* organization.
(*That is, independent of the Nuclear Regulatory Commission and the nuclear industry.)
Safety and Security of Pool Storage
FINDING 3A: Pool storage is required at all operating commercial nuclear power plants to cool newly discharged spent fuel. No change.
FINDING 3B: The committee finds that, under some conditions, a terrorist attack that partially or completely drained a spent fuel pool could lead to a propagating zirconium cladding fire and the release of large quantities of radioactive materials to the environment. Details are provided in the committee’s classified report. FINDING 4.4: The present committee does not have a sufficient information to reevaluate Finding 3B in NRC (2004) because the U.S. Nuclear Regulatory Commission has not examined the specific terrorist attack scenarios identified in that report (see Recommendation 3E-1 in NRC [2004]).
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
Findings and recommendations from NRC (2006) Present committee’s reevaluation of findings and recommendations in NRC (2006)
FINDING 3C: It appears to be feasible to reduce the likelihood of a zirconium cladding fire following a loss-of-pool-coolant event using readily implemented measures. FINDING 4.5: Technical analyses undertaken by the U.S. Nuclear Regulatory Commission and Sandia National Laboratories after 2004 confirm that reconfiguring spent fuel in pools can be an effective strategy for reducing the likelihood of fuel damage and zirconium cladding fires following loss-of-pool-coolant events. However, reconfiguring spent fuel in pools does not eliminate the risks of zirconium cladding fires, particularly during certain periods following reactor shutdowns or for certain types of pool drainage conditions. These technical studies also illustrate the importance of maintaining water coolant levels in spent fuel pools so that fuel assemblies do not become uncovered.
FINDING 3D: The potential vulnerabilities of spent fuel pools to terrorist attacks are plant-design specific. Therefore, specific vulnerabilities can be understood only by examining the characteristics of spent fuel storage at each plant. No change.
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
Findings and recommendations from NRC (2006) Present committee’s reevaluation of findings and recommendations in NRC (2006)
FINDING 3E: The Nuclear Regulatory Commission and independent analysts have made progress in understanding some vulnerabilities of spent fuel pools to certain terrorist attacks and the consequences of such attacks for releases of radioactivity to the environment. However, additional work on specific issues is needed urgently. FINDING 4.6: Additional analyses and physical experiments carried out by the U.S. Nuclear Regulatory Commission and Sandia National Laboratories since NRC (2006) was completed have substantially improved the state of knowledge of boiling water reactor (BWR) and pressurized water reactor (PWR) spent fuel behavior following partial or complete loss of pool water. These studies and experiments have addressed the following important issues:
RECOMMENDATION (3E-1): The Nuclear Regulatory Commission should undertake additional best-estimate analyses to more fully understand the vulnerabilities and consequences of loss-of-pool-coolant events that could lead to a zirconium cladding fire. Based on these analyses, the Commission should take appropriate actions to address any significant vulnerabilities that are identified. The analyses of the BWR and PWR spent fuel pools should be extended to consider the consequences of loss-of-pool-coolant events that are described in the committee’s classified report. The consequence analyses should address the following questions:
  • Fuel damage state and timing as a function of fuel age and pool water loss.
  • Propagation of zirconium cladding fires to other assemblies in the pool.
  • Potential mitigation strategies (dispersion of hot fuel assemblies in the pool, water sprays, water replacement) for delaying or preventing fuel damage following pool water loss.
These experiments have resulted in significant validation of the Methods for Estimation of Leakages and Consequences of Releases (MELCOR) code that is used to model coolant loss in spent fuel pools. However, the code is unable to adequately model flows when stratification occurs and plumes form in the pool and/or above-pool environment. Moreover, key portions of code lack validation, and there has been no end-to-end validation of the code for modeling coolant loss in spent fuel pools.
  • To what extent would such attacks damage the spent fuel in the pool, and what would be the thermal consequences of such damage?
  • Is it feasible to reconfigure the spent fuel within pools to prevent zirconium cladding fires given the actual characteristics (i.e., heat generation) of spent fuel assemblies in the pool, even if the fuel were damaged in an attack? Is there enough space in the pools at all commercial reactor sites to implement such fuel reconfiguration?
  • In the event of a localized zirconium cladding fire, will such rearrangement prevent its spread to the rest of the pool?
  • How much spray cooling is needed to prevent zirconium cladding fires and prevent propagation of such fires? Which of the different options for providing spray cooling are effective under attack and accident conditions?
RECOMMENDATION 4.6 The U.S. Nuclear Regulatory Commission should (1) sponsor an end-to-end validation of the MELCOR code for use in modeling coolant loss in spent fuel pools, and (2) validate key submodels in the code with particular attention paid to
  • Modeling the thermal and chemical behavior of spent fuel assemblies in partially drained pools.
  • Modeling the thermal and chemical response of spent fuel assemblies to the application of water sprays.
  • Modeling and validating for stratified flows in fully and partially drained pools.
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
Findings and recommendations from NRC (2006) Present committee’s reevaluation of findings and recommendations in NRC (2006)
Sensitivity analyses should also be undertaken to account for the full range of variation in spent fuel pool designs (e.g., rack designs, capacities, spent fuel burn-ups, and ages) at U.S. commercial nuclear power plants. FINDING 4.7: The U.S. Nuclear Regulatory Commission has not analyzed the vulnerabilities of spent fuel pools to the specific terrorist attack scenarios identified in Recommendation 3E-1 in NRC (2004).
FINDING 4.8: The U.S. Nuclear Regulatory Commission and the U.S. nuclear industry have made good progress in implementing actions to address Recommendation 3E-2 in NRC (2006). The U.S. Nuclear Regulatory Commission has directed plant licensees to
RECOMMENDATION (3E-2): While the work described in the previous recommendation under Finding 3E, above, is being carried out, the Nuclear Regulatory Commission should ensure that power plant operators take prompt and effective measures to reduce the consequences of loss-of-pool-coolant events in spent fuel pools that could result in propagating zirconium cladding fires. The committee judges that there are at least two such measures that should be implemented promptly:
  • Reconfigure their spent fuel in pools to achieve at least a 1 × 4 dispersion of high- and low-decay-heat assemblies, unless such configuration can be shown to be inapplicable or unachievable. This configuration must be achieved following each fuel offload from the reactor not later than 60 days after reactor shutdown.
  • Develop guidance and implement strategies to maintain and restore spent fuel pool cooling following explosions and fires. To address this requirement, the U.S. nuclear industry has developed and adopted guidance and strategies for spent fuel pool water makeup and water sprays.
  • Reconfiguring of fuel in the pools so that high decay-heat fuel assemblies are surrounded by low decay-heat assemblies. This will more evenly distribute decay-heat loads, thus enhancing radiative heat transfer in the event of a loss of pool coolant.
  • Provision for water-spray systems that would be able to cool the fuel even if the pool or overlying building were severely damaged.
However, additional work is needed to more fully implement Recommendation 3E-2 in NRC (2006).
RECOMMENDATION 4.8: The U.S. Nuclear Regulatory Commission should take the following actions to more fully implement Recommendation 3E-2 in NRC (2006):
  • Reexamine the need for the 60-day limit for fuel dispersion and reduce the allowable time if feasible.
  • Reexamine and, if needed, redesign the water makeup and spray systems and strategies to ensure that they can be implemented when physical access to pools is hindered or the site becomes inaccessible.
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
Findings and recommendations from NRC (2006) Present committee’s reevaluation of findings and recommendations in NRC (2006)
Safety and Security of Dry Cask Storage and Comparison with Pool Storage
FINDING 4A: Although there are differences in the robustness of different dry cask designs (e.g., bare fuel versus canister based), the differences are not large when measured by the absolute magnitudes of radionuclide releases in the event of a breach. FINDING 4.9: Additional analyses on dry cask vulnerabilities have been undertaken since NRC (2006) was completed. This work was still under way when the present report was being completed; consequently, the committee was unable to evaluate its technical soundness and completeness.
FINDING 4B: Additional steps can be taken to make dry casks less vulnerable to potential terrorist attacks. FINDING 4.10: The U.S. Nuclear Regulatory Commission is incorporating the results of its dry cask vulnerability analyses into its regulations through rulemaking. The rulemaking was still in progress when the present study was being completed; consequently, the committee was unable to evaluate its technical soundness and completeness.
Note: Section 4.2.3 in the unclassified (2006) report lists such steps: Adding additional surveillance; adding berms; adding visual barriers; increasing spacing between casks or adding shims; making relatively minor changes in cask designs.
RECOMMENDATION 4.10: The U.S. Nuclear Regulatory Commission should give high priority to completing its analyses on dry cask storage vulnerabilities and rulemaking.
RECOMMENDATION (4B): The Nuclear Regulatory Commission should consider using the results of the vulnerability analyses for possible upgrades of requirements in 10 CFR 72 for dry casks, specifically to improve their resistance to terrorist attacks.
FINDING 4C: Dry cask storage does not eliminate the need for pool storage at operating commercial reactors. No change.
FINDING 4D: Dry cask storage for older, cooler spent fuel has two inherent advantages over pool storage: (1) It is a passive system that relies on natural air circulation for cooling, and (2) it divides the inventory of that spent fuel among a large number of discrete, robust containers. These factors make it more difficult to attack a large amount of spent fuel at one time and also reduce the consequences of such attacks. No change.
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
Findings and recommendations from NRC (2006) Present committee’s reevaluation of findings and recommendations in NRC (2006)
FINDING 4E: Depending on the outcome of plant-specific vulnerability analyses described in the committee’s classified report, the Nuclear Regulatory Commission might determine that earlier movements of spent fuel from pools into dry cask storage would be prudent to reduce the potential consequences of terrorist attacks on pools at some commercial nuclear plants. FINDING 4.11: The U.S. Nuclear Regulatory Commission has completed a technical analysis of spent fuel pool accident consequences to inform a regulatory decision on expedited transfer of spent fuel from pool to dry cask storage. The analysis was carried out in accordance with prescribed U.S. Nuclear Regulatory Commission regulatory guidance and provides valuable technical information about the impacts of various accident scenarios on spent fuel storage in pools. However, the analysis did not consider spent fuel storage sabotage risks, dry cask storage risks, or certain health consequences that would likely result from a severe nuclear accident. The analysis also used simplifying bounding assumptions that make it technically difficult to assign confidence intervals to the consequence estimates or make valid risk comparisons. A risk assessment that evaluates the three questions of the risk triplet and that accounts for uncertainties in both probability and consequence estimates is needed to address Finding 4E in NRC (2006) to determine whether “earlier movements of spent fuel from pools into dry cask storage would be prudent to reduce the potential consequences of terrorist attacks on pools at some commercial nuclear plants.”
RECOMMENDATION 4.11: The U.S. Nuclear Regulatory Commission should perform a spent fuel storage risk assessment to elucidate the risks and potential benefits of expedited transfer of spent fuel from pools to dry casks. This risk assessment should address accident and sabotage risks for both pool and dry storage. The sabotage risks should be assessed using the methodology developed in response to the present committee’s Recommendation 4.1B.
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
Findings and recommendations from NRC (2006) Present committee’s reevaluation of findings and recommendations in NRC (2006)
Implementation Issues
FINDING 5A: Security restrictions on sharing of information and analyses are hindering progress in addressing potential vulnerabilities of spent fuel storage to terrorist attacks. FINDING 4.12: The U.S. Nuclear Regulatory Commission has made a commendable effort to improve the sharing of pertinent information on vulnerability and consequence analyses of spent fuel storage with nuclear power plant operators and dry cask storage system vendors. The Commission has sponsored key staff at these organizations for national security clearances, regularly shares important security-related information and threat-related intelligence with industry groups, and is responsive to industry requests for information.
RECOMMENDATION (5A): The Nuclear Regulatory Commission should improve the sharing of pertinent information on vulnerability and consequence analyses of spent fuel storage with nuclear power plant operators and dry cask storage system vendors on a timely basis.
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

APPENDIX 4A
Dry Cask Storage Regulations

There are two types of USNRC licenses for dry storage of spent fuel:

  1. A site-specific license issued under 10 CFR Part 72 (Licensing Requirements for the Independent Storage of Spent Nuclear Fuel, High-Level Radioactive Waste, and Reactor-Related Greater Than Class C Waste) for an Independent Spent Fuel Storage Installation1 (ISFSI) either on- or offsite, and
  2. A general license granted under 10 CFR Part 72 to 10 CFR Part 50 (Domestic Licensing of Production and Utilization Facilities) licensees under certain conditions.

A site-specific license requires an application, with supporting documentation, which upon approval culminates in a license issued to the installation. A general license is granted by the regulations if the installation meets certain conditions. There were 14 sites that dry-store spent fuel under site-specific licenses2 and 60 sites that dry-store spent fuel under a general license in the United States as of August 13, 2015.3

Security requirements under each type of license can vary depending on whether the storage facility is (1) co-located with an operating reactor, (2) co-located with a decommissioned reactor, or (3) located offsite. Generally, the first two types of storage facilities may be generally or specifically licensed but the third type must be specifically licensed; consequently, there are three different sets of requirements found in regulation, license conditions, and emergency orders enforced by the USNRC (see Figure 4A.1).

Emergency response planning requirements for dry storage facilities may also vary depending on whether the reactor is operational or decommissioned and whether the facility is located on- or offsite. Location-based (i.e., facility located on- or offsite) variations in planning requirements are generally regulation driven, whereas reactor status-based (i.e., reactor operating or decommissioned) variations are usually exemption driven. Licensees that dry-store spent fuel at generally licensed sites that are co-located with a reactor may request exemptions from certain emergency planning

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1 An ISFSI is a facility used to store spent nuclear fuel and certain other types of radioactive material (e.g., greater-than-class-C low-level waste) on an interim basis. The USNRC considers an ISFSI to be “independent” even when it is co-located with another USNRC-licensed facility such as a power reactor.

2 Additionally, one site (GE Morris, located near Chicago, Illinois) operates a pool-storage facility under a site-specific license.

3 See http://pbadupws.nrc.gov/docs/ML1524/ML15240A058.pdf.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×
Image
FIGURE 4A.1 Current USNRC security regulations for ISFSIs. SOURCE: USNRC (2009a, Figure 1).

requirements once there is a permanent cessation of operations and fuel has been removed from the reactor vessel.4

Owing to this complicated regulatory scheme, it is not a simple matter to assess the overall security and safety of ISFSIs. A complete assessment would require a case-by-case evaluation of each facility under its applicable requirements, physical configuration, and other site-specific information. The USNRC has pointed out that “continuing differences between general-license and specific license ISFSI security requirements is not appropriate and does not contribute to long term regulatory stability or to stakeholder support and understanding of the Commission’s regulatory programs for storing spent fuel” (USNRC, 2007a, Enclosure 3, p. 9).

Following the September 11, 2001, terrorist attacks on the United States, the USNRC carried out an evaluation of its regulatory program for spent fuel storage and initiated a rulemaking (USNRC, 2009a) “to create a more consistent and coherent regulatory structure for these types of waste storage facilities.” The USNRC decided to undertake a new security

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4 NSIR/DPR-ISG-02, Interim Staff Guidance, Emergency Planning Exemption Requests for Decommissioning Nuclear Power Plants.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
×

rulemaking that is risk informed and performance based. “Risk informed” refers to a vulnerability assessment methodology that takes into consideration both threat- and non-threat-based information. “Performance based” refers to the application of a dose acceptance limit to ISFSIs. According to the USNRC, radiological sabotage scenarios would be developed, and ISFSIs would be expected to provide high assurance that a 5-rem lifetime dose to the maximally exposed individual would not be exceeded at the facility boundary.

The security requirements are expected to be captured in a regulatory guidance document. USNRC staff will develop these security requirements from a vulnerability perspective (not a threat perspective). Based on this guidance, ISFSIs would be subjected to an analysis to determine whether they meet the dose-limit requirements. All ISFSIs would be held to the same standard of protection regardless of whether they are licensed under 10 CFR Part 50 or 10 CFR Part 72. The USNRC judges that this approach would be relatively simple for current ISFSIs to satisfy (assuming that they now can meet the 5-rem standard) but would move away from the design-basis-threat requirement that now applies to most ISFSIs (USNRC, 2007a, Enclosure 3).

At the time the present report was being written, the USNRC’s ISFSI security rulemaking actions had not been completed, and the future of this rulemaking is uncertain. On October 6, 2015, the Commission approved a 5-year delay in the commencement of this rulemaking.5 In the memorandum that discusses this decision, the USNRC staff notes that this rulemaking could be accelerated under certain circumstances. It also notes that at the end of this 5-year period “the staff should re-evaluate whether rulemaking in this area is warranted.” Therefore, it is premature for the present committee to comment on possible changes to the regulatory framework. Nevertheless, the committee recommends (Recommendation 4.10) that the USNRC give high priority to completing its analyses on dry cask storage vulnerabilities and rulemaking.

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5 See http://pbadupws.nrc.gov/docs/ML1528/ML15280A105.pdf.

Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
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Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
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Page 110
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
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Page 111
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
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Page 112
Suggested Citation:"4 Reevaluation of Findings and Recommendations from Previous NAS Reports." National Academies of Sciences, Engineering, and Medicine. 2016. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants: Phase 2. Washington, DC: The National Academies Press. doi: 10.17226/21874.
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The U.S. Congress asked the National Academy of Sciences to conduct a technical study on lessons learned from the Fukushima Daiichi nuclear accident for improving safety and security of commercial nuclear power plants in the United States. This study was carried out in two phases: Phase 1, issued in 2014, focused on the causes of the Fukushima Daiichi accident and safety-related lessons learned for improving nuclear plant systems, operations, and regulations exclusive of spent fuel storage. This Phase 2 report focuses on three issues: (1) lessons learned from the accident for nuclear plant security, (2) lessons learned for spent fuel storage, and (3) reevaluation of conclusions from previous Academies studies on spent fuel storage.

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