This appendix describes some key actions being taken by the U.S. nuclear industry and the U.S. Nuclear Regulatory Commission (USNRC) as a direct result of the Fukushima Daiichi accident.
The USNRC took several near-term actions in the weeks following the Fukushima Daiichi accident:
• On March 18, 2011, the USNRC issued Information Notice 2011-05,1 “Tohoku-Taiheiyou-Oki Earthquake Effects on Japanese Nuclear Power Plants.” This notice was intended to “inform [U.S. nuclear plant licensees] of effects of the Tohoku-Taiheiyou-Oki Earthquake [Great East Japan Earthquake] on nuclear power plants in Japan. The [US]NRC expects that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems.”
• On May 11, 2011, the USNRC issued Bulletin 2011-01,2 “Mitigating Strategies,” requiring that licensees “provide a comprehensive verification of their compliance with the regulatory requirements of Title 10 of the Code of Federal Regulations (10 CFR) Section 50.54(hh)(2)” and “to determine if 1) additional assessment of program implementation is needed,
1 Available at http://pbadupws.nrc.gov/docs/ML1107/ML110760432.pdf.
2 Available at http://pbadupws.nrc.gov/docs/ML1112/ML111250360.pdf.
• On May 23, 2011, the USNRC issued Temporary Instruction 2515/183,3 “Followup to the Fukushima Daiichi Nuclear Station Fuel Damage Event.” This instruction was intended to “independently assess the adequacy of actions taken by licensees in response to the Fukushima Daiichi nuclear station fuel damage event. The inspection results from this TI will be used to evaluate the industry’s readiness for a similar event and to aid in determining whether additional regulatory actions by the U.S. Nuclear Regulatory Commission are warranted.”
• On March 23, 2011, the chairman of the USNRC directed the agency’s executive director of operations to establish a task force composed of senior-level staff to conduct a review of the agency’s processes and regulations and make recommendations to improve them.4 A six-member task force, the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident (NTTF), was established to undertake this review.
• On April 29, 2011, the USNRC issued Temporary Instruction 2515/184,5 “Availability and Readiness Inspection of Severe Accident Management Guidelines (SAMGs).” This instruction was intended to “[d]etermine that the severe accident management guidelines (SAMGs) are available and how they are being maintained” and also “[d]etermine the nature and extent of licensee implementation of SAMG training and exercises.”
The NTTF delivered its report on July 17, 2011. The NTTF concluded that
a sequence of events like the Fukushima accident is unlikely to occur in the United States and some appropriate mitigation measures have been implemented, reducing the likelihood of core damage and radiological releases. Therefore, continued operation and continued licensing activities do not pose an imminent risk to public health and safety. (USNRC NTTF, 2011, p. vii)
The NTTF also found that
the Commission’s longstanding defense-in-depth philosophy, supported and modified as necessary by state-of-the-art probabilistic risk assessment techniques, should continue to serve as the primary organizing principle of its regulatory framework. The Task Force concludes that the applica
3 Available at http://pbadupws.nrc.gov/docs/ML1107/ML11077A007.pdf.
5 Available at http://pbadupws.nrc.gov/docs/ML1111/ML11115A053.pdf.
tion of the defense-in-depth philosophy can be strengthened by including explicit requirements for beyond-design-basis events. (USNRC NTTF, 2011, p. viii)
The NTTF recommended a series of 12 broad actions “to clarify and strengthen the regulatory framework for protection against natural disasters, mitigation, and emergency preparedness, and to improve the effectiveness of the NRC’s programs” (USNRC NTTF, 2011, p. viii). These were the following:
Clarifying the Regulatory Framework
1. The Task Force recommends establishing a logical, systematic, and coherent regulatory framework for adequate protection that appropriately balances defense-in-depth and risk considerations.
2. The Task Force recommends that the NRC require licensees to reevaluate and upgrade as necessary the design-basis seismic and flooding protection of structures, systems, and components for each operating reactor.
3. The Task Force recommends, as part of the longer term review, that the NRC evaluate potential enhancements to the capability to prevent or mitigate seismically induced fires and floods.
4. The Task Force recommends that the NRC strengthen station blackout mitigation capability at all operating and new reactors for design-basis and beyond-design-basis external events.
5. The Task Force recommends requiring reliable hardened vent designs in boiling water reactor facilities with Mark I and Mark II containments.
6. The Task Force recommends, as part of the longer term review, that the NRC identify insights about hydrogen control and mitigation inside containment or in other buildings as additional information is revealed through further study of the Fukushima Dai-ichi accident.
7. The Task Force recommends enhancing spent fuel pool makeup capability and instrumentation for the spent fuel pool.
8. The Task Force recommends strengthening and integrating onsite emergency response capabilities such as emergency operating procedures, severe accident management guidelines, and extensive damage mitigation guidelines.
Strengthening Emergency Preparedness
9. The Task Force recommends that the NRC require that facility emergency plans address prolonged station blackout and multiunit events.
10. The Task Force recommends, as part of the longer term review,
that the NRC pursue additional emergency preparedness topics related to multiunit events and prolonged station blackout.
11. The Task Force recommends, as part of the longer term review, that the NRC should pursue emergency preparedness topics related to decisionmaking, radiation monitoring, and public education.
Improving the Efficiency of NRC Programs
12. The Task Force recommends that the NRC strengthen regulatory oversight of licensee safety performance (i.e., the Reactor Oversight Process) by focusing more attention on defense-in-depth requirements consistent with the recommended defense-in-depth framework. (USNRC NTTF, 2011, p. ix)
The USNRC is using these Near-Term Task Force recommendations as the basis for developing regulatory actions. By the first anniversary of the Fukushima Daiichi accident, several regulatory actions had already been taken. These included requests for information from nuclear plant licensees, orders for immediate actions, and regulatory rulemaking. These actions are summarized in Table F.1 and described below.
TABLE F.1 Summary of USNRC Actions following the Fukushima Nuclear Accident Through May 2014
|Seismic and flood walkdownsa
|Inspect existing protection features against seismic and flood design-basis events; correct degraded conditions
|Reanalyze potential seismic effects using present-day information to determine if safety upgrades are needed
|Reanalyze potential flooding effects using present-day information to determine if safety upgrades are needed
|Assess staffing needs and communication capabilities to effectively respond to an event affecting multiple units
|Spent fuel pool instrumentatione
|Provide a reliable wide-range indication of water level in spent fuel storage pools
|Provide a reliable hardened containment vent system for BWRs with Mark I or Mark II containment systems
|Enhance the capability to maintain plant safety during a prolonged loss of electrical power
|SBO mitigation strategiesf
|Enhance the capability to maintain plant safety during a prolonged loss of electrical power
|Onsite emergency response proceduresh
|Strengthen and integrate different types of emergency procedures and capabilities at nuclear plants
|Filtration and confinement strategiese
|Evaluate potential strategies that may further confine or filter radioactive materials if core damage occurs
|Consider a revised risk-informed regulatory framework that affects reactor oversight process
|Still in process
a http://pbadupws.nrc.gov/docs/ML1212/ML12129A108.pdf (June 27, 2012); http://pbadupws.nrc.gov/docs/ML1215/ML12156A052.pdf (July 6, 2012)
b http://pbadupws.nrc.gov/docs/ML1228/ML12286A029.pdf (November 12, 2012); http://pbadupws.nrc.gov/docs/ML1310/ML13106A331.pdf (May 7, 2013).
c http://pbadupws.nrc.gov/docs/ML1231/ML12311A214.pdf (November 30, 2013); http://pbadupws.nrc.gov/docs/ML1231/ML12314A412.pdf (January 4, 2013).
d http://pbadupws.nrc.gov/docs/ML1205/ML12053A340.pdf (March 12, 2012); http://pbadupws.nrc.gov/docs/ML1212/ML12125A412.pdf (May 2012).
ehttp://pbadupws.nrc.gov/docs/ML1205/ML12056A044.pdf (March 12, 2012); http://pbadupws.nrc.gov/docs/ML1222/ML12221A339.pdf (August 29, 2012).
f http://pbadupws.nrc.gov/docs/ML1314/ML13143A321.pdf (June 6, 2013)
g http://pbadupws.nrc.gov/docs/ML1205/ML12054A735.pdf (March 12, 2012); http://pbadupws.nrc.gov/docs/ML1222/ML12229A174.pdf (August 29, 2012); http://pbadupws.nrc.gov/docs/ML1224/ML12242A378.pdf (August 2012).
F.1.1 Seismic and Flooding Walkdowns
The USNRC concluded that U.S. nuclear plants needed to reconfirm their existing ability to resist seismic and flooding events. On March 12, 2012, the USNRC requested that plant licensees perform detailed inspections (“walkdowns”) of their currently installed seismic and flooding pro
tection features. Licensees were asked to ensure that the plant features met current requirements, and also identify, correct, and report any degraded conditions. The plants completed their walkdowns by November 2012. The USNRC has carried out follow-up inspections, and the agency’s technical experts are reviewing licensee walkdown reports.
F.1.2 Seismic and Flooding Reevaluations
Licensees were directed to reevaluate earthquake and flooding hazards that could impact their plant sites. The evaluation is to determine whether plant structures, systems, and/or components need to be updated to protect against these hazards. The USNRC will review each step in the analysis process and take action to require plant changes as necessary.
F.1.3 Emergency Preparedness
The USNRC directed licensees to assess how many emergency staff they will need to respond to a large accident that could affect multiple reactors at their sites and to make changes to their emergency plans as necessary. The USNRC also directed licensees to ensure that plants can maintain communications equipment that their staff will need to effectively respond to such an accident (e.g., radios for response teams, cellular telephones, and satellite telephones).
F.1.4 Spent Fuel Pool Instrumentation Order
The USNRC issued an order on March 12, 2012, requiring that licensees install additional water-level instrumentation in the spent fuel pools at their plants. The instrumentation must remotely report at least three distinct water levels: (1) normal level, (2) low level but adequate to shield workers from radiation, and (3) a level near the top of the spent fuel rods where more water should be added without delay.
F.1.5 Containment Venting Systems Order
The USNRC issued an order on March 12, 2012, requiring all licensees of boiling water reactors with Mark I and Mark II containments to install reliable, hardened vents that can be used to vent containments. After issuing the order, additional USNRC evaluations examined the benefits of venting after reactor core damage occurs. In June 2013, the USNRC modified the order to ensure that those vents will remain functional if the reactor core is damaged.
F.1.6 Hardened Vents and Filtration Rulemaking
The USNRC is evaluating the need for filtered vents in Mark I and Mark II containments through the agency’s rulemaking process.
F.1.7 Mitigation Strategies Order
The USNRC issued an order on March 12, 2012, requiring licensees of U.S. nuclear plants to implement strategies for coping without permanent electrical power sources for an indefinite period of time. These strategies are expected to utilize currently installed equipment (e.g., pumps that are powered by steam rather than by electrical power), portable equipment stored onsite, and equipment that can be shipped to the site.
F.1.8 Station Blackout Mitigation Strategies Rulemaking
The USNRC is conducting a rulemaking to permanently write into the agency’s rules the requirements imposed by the Mitigation Strategies Order.
F.1.9 Onsite Emergency Response Capabilities Rulemaking
The USNRC is conducting a rulemaking to strengthen and integrate emergency response capabilities at U.S. nuclear plants. Currently, U.S. plants may have several categories of response procedures that they draw upon, depending on the nature of the incident. This rulemaking will establish standards to ensure that the plants can smoothly transition between these procedures while keeping plants’ overall strategies coherent and comprehensive. The new rule will also require plants to improve strategies for large-scale events to promote effective decision making at all levels. The rule will include training, qualification, and evaluation requirements for the key personnel expected to implement the procedures and strategies.
F.1.10 Risk-Informed Regulatory Framework
The task force recommended that the NRC establish a logical, systematic, and coherent regulatory framework that appropriately balances multiple layers of protection and risk considerations to deal with beyond-design-basis events. This work is still in the process of being reviewed in connection with the Task Force Report on a Proposed Risk Management Regulatory Framework (USNRC, 2012a).
The U.S. nuclear industry, led by the Nuclear Energy Institute, Institute of Nuclear Power Operations, and Electric Power Research Institute, initiated a voluntary effort to integrate and coordinate the industry’s response to the Fukushima Daiichi accident (NEI, 2012). The industry developed the “Diverse and Flexible Coping Strategies (FLEX) Implementation Guide” (NEI, 2012) to satisfy the USNRC’s Mitigation Strategies Order.
FLEX is intended to augment plant coping capabilities (Figure F.1) for external beyond-design-basis (BDB) events. The strategy itself consists of the following four elements:
1. To have portable backup equipment capable of providing water and power to the reactor. Such equipment includes, for example, electrical generators, batteries, and battery chargers; compressors; pumps, hoses, and couplings; equipment for clearing debris; and equipment for temporary protection against flooding;
2. To stage this equipment in locations both onsite and offsite where it will be safe and deployable during a BDB external event;
3. To develop procedures and guidance for implementing FLEX;
4. To develop programmatic controls that will ensure personnel are well trained and equipment is maintained;
FIGURE F.1 FLEX is intended to augment coping capabilities for beyond-design-basis events involving the simultaneous loss of emergency AC power and ultimate heat sink at all units at a nuclear plant, thereby increasing defense in depth. SOURCE: NEI (2012).
Because each reactor has unique features, FLEX implementation is unit specific. Plants establish a baseline of current capabilities for coping with extreme events, assuming the following initial and boundary conditions:
• An external event impacts all units at a site.
• Initially the reactors are operating at power and then are safely shut down.
• No additional initiating events or failures are assumed to occur immediately prior to or during the event.
• All staff, at the minimum staffing levels, are available to help.
The plant then examines the likelihood and impacts of the following extreme external events:
• Large earthquakes,
• External flooding,
• Intense storms (e.g., hurricanes, high winds, tornados), and
• Extreme snow, ice, cold, and heat.
The plant then develops implementation procedures for the protection and deployment of equipment, procedural interfaces, and utilization of offsite resources for each of these events. Finally, plants use this analysis to identify needed enhancements to baseline capabilities.
NEI submitted a final draft of the FLEX plan to the USNRC in August 2012. The USNRC issued a statement and interim staff guidance (USNRC, 2012c) concluding that the FLEX plan successfully implements the Mitigation Strategies Order and is an acceptable approach to meet the December 31, 2016, compliance deadline in that order.