March 30, 2015 

MEMORANDUM TO: Mark A. Satorius 

 Executive Director for Operations 

FROM: Annette L. Vietti-Cook, Secretary /RA/ 

SUBJECT: STAFF REQUIREMENTS – COMSECY-14-0037– INTEGRATION 

OF MITIGATING STRATEGIES FOR BEYOND-DESIGN-BASIS 

EXTERNAL EVENTS AND THE REEVALUATION OF FLOODING 

HAZARDS 

The Commission has approved the staff’s recommendation 1 that licensees for operating 

nuclear power plants need to address the reevaluated flooding hazards within their mitigating 

strategies for beyond-design-basis external events; and recommendation 2 that licensees for 

operating nuclear power plants may need to address some specific flooding scenarios that 

could significantly damage the power plant site by developing targeted or scenario-specific 

mitigating strategies, possibly including unconventional measures, to prevent fuel damage in 

reactor cores or spent fuel pools. However, for recommendation 2, the Commission notes that it 

is within the staff's authority, and is the staff's responsibility, to determine, on a plant-specific 

basis, whether targeted or scenario-specific mitigating strategies, possibly including 

unconventional measures, are acceptable. 

The Commission has disapproved the staff’s recommendation 3 that the staff should revise the 

Near Term Task Force (NTTF) Recommendation 2.1 flooding assessments and integrate the 

Phase 2 decision-making into the development and implementation of mitigating strategies in 

accordance with the Mitigating Strategies Order and the related mitigation of beyond-designbasis events (MBDBE) rulemaking. Instead, the staff should reassess the guidance developed 

for the Phase 1 integrated assessments. In addition, the staff should also develop the criteria 

and guidance for Phase 2 of the flooding reevaluations. 

In reassessing the Phase 1 integrated assessment guidance, the staff should: 

a. Include a graded approach for determining the need for, and prioritization and scope of, 

plant-specific integrated assessments so that the integrated assessments are focused 

on those plants where there is the greatest opportunity for additional safety 

enhancements. 

b. Use resources judiciously, and be risk-informed and performance-based, to the extent 

practicable, to reduce any unnecessary conservatisms and identify any areas with 

insufficient conservatisms. 
c. Evaluate potential changes to the guidance to introduce more realism for the purpose of 

identifying potential safety enhancements for operating reactors. For example, for local 

precipitation events, the staff should examine whether it is necessary for the licensee to 

assume that drains are clogged if there is a commitment for periodic surveillance of the 

drains, and if plant procedures call for verifying that drains are clear when a precipitation 

event is forecast. 

d. Focus on flood scenarios that could result in cliff-edge effects and where substantial 

safety benefits can be achieved, rather than on scenarios where limited risk 

improvements are expected. In doing so, the staff should continue to use engineering 

judgment and consider the qualitative likelihood of initiating events when quantitative 

tools and data are not available. For example, the staff should examine whether, at the 

time of a seismic event, dams and rivers should be assumed to be at nominal or typical 

levels, consistent with normal dam operating practices and procedures rather than at 

maximum levels. 

e. Consider available physical margin data in order to assess the flooding vulnerability for 

each site. 

In developing the Phase 2 acceptance criteria and guidance, the staff should: 

a. Add clarity on how Phase 2 decisions about whether further regulatory actions are 

necessary will be made within the current regulatory process, including the Backfit Rule. 

b. Allow flexibility in the way in which licensees address vulnerabilities identified through 

the integrated assessment process that relied on hazards developed using guidance for 

new plants. That flexibility should include the opportunity for licensees to demonstrate 

that vulnerabilities identified may be less risk significant when more realistic assumptions 

are applied in the analyses. 

c. Take into account the fact that the licensees are protecting mitigating strategies 

equipment from the reevaluated flood hazard developed in accordance with the 50.54(f) 

letter and the associated guidance. 

d. Consider an appropriate balance between protection and mitigation based on the 

principle of defense-in-depth. 

The NRC staff should continue to work with licensees toward the expeditious completion 

of the flooding hazard reevaluations in order to ensure that flooding hazards are understood for 

every site using the current flooding regulations and guidance. The closure of the § 50.54(f) 

letter should proceed in parallel with implementation and closure of Order EA-12-049 and the 

associated MBDBE rulemaking and should not impact the schedule for these actions. 

The NRC staff should also proceed expeditiously to clearly define the steps needed to complete 

our actions in response to NTTF Recommendation 2.1 for flooding and, within three months of 

the date of the SRM for COMSECY-14-0037, provide a plan for achieving closure of this 

recommendation to the Commission for review and approval. The plan should ensure 

completion of the Mitigating Strategies Orders and MBDBE rulemaking on the current schedule 

and provide target closure dates for the revised Phase 1 integrated assessment guidance and 

development of criteria and guidance for Phase 2. The plan should consider when the ACRS 
should be given the opportunity to review the Phase 1 integrated assessment revised guidance 

and Phase 2 criteria and guidance. 

 (EDO) (SECY Suspense: 6/30/15) 

Future updates of post-Fukushima measures should provide more detailed information on the 

status of the flooding hazard reevaluations and integrated assessments, as well as the Phase 1 

and Phase 2 guidance. 

cc: Chairman Burns 

 Commissioner Svinicki 

 Commissioner Ostendorff 

 Commissioner Baran 

 OGC 

 CFO 

 OCA 

 OPA