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2024.12.12 NEI Wp Selection of Seismic Scenario for EPZ Determination - Response to NRC Staff (Updated)
	ML25043A204
Person / Time
Site:	Nuclear Energy Institute
Issue date:	12/12/2024
From:	; Nuclear Energy Institute
To:	; Office of Nuclear Reactor Regulation
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Response to NRC Comments & Questions on Subject NEI White Paper

©2025 Nuclear Energy Institute 3 Please discuss how the approach can be implemented at the construction permit stage The design of the SSCs will already be at the stage where a margin assessment can be performed. This being the case, the fragility parameters will be available that are needed to perform the calculation of C10%. This will be shown in a Tabletop.

Level-3 PRA is not required. All that is needed is a source term and dose calculation model that can be set up to evaluate the specified seismic scenario (plant damage state). This will be shown in the Tabletop.

Comment/Question #1

©2025 Nuclear Energy Institute 4 Please discuss (i) appropriateness of C10% criterion (2 x GMRS), and (ii) assumption that any SSC that has C10% capacity greater than 2 x GMRS is considered fully successful (i) is shown to be appropriate through the detailed analysis provided in Section 5 of the NEI White Paper. As explained, a holistic consideration of the insights from past SPRAs with knowledge of the safety improvements in new plant designs indicates that a scenario based on 2 x GMRS adequately represents the conditions where emergency response should be required.

(ii) is based on the approach approved by NRC for use in the assessment of seismic MSA per R.G. 1.226, which endorses NEI 12-06. The use of the C10% as a pass-fail criterion for success is a fundamental part of Appendix H of NEI 12-06.

Comment/Question #2

The check for cliff edge effects is discussed in Section 10 of the NEI White Paper. The scenario (plant damage state) will add the additional failures of any SSCs whose C10% is within 10% of 2 x GMRS. This captures the concept of what would be the impact on the results of a step increase in the earthquake severity.

This will be illustrated in the Tabletop.

Comment/Question #2 (continued)

It will be stated that the GMRS to be used is that specified in R.G. 1.208, i.e., a site-specific, performance-based GMRS, satisfying the requirements of paragraphs (c), (d)(1), and (d)(2) of 10 CFR 100.23, and leading to the establishment of an SSE to satisfy the design requirements of Appendix S to 10 CFR Part 50.

This is what was used as the basis for the evaluations in the NEI White Paper.

Comment/Question #3

©2025 Nuclear Energy Institute 7 It is not clear why the cut-o of 1.0g PGA is needed and is appropriate for sites with higher seismicity. In addition, PGA, as a ground motion measure, is by itself, not a good determinant for damage.

As discussed in Section 6 of the NEI White Paper, there is a need to establish some upper severity above which Emergency Planning is not practical, accounting for the post-earthquake status of the necessary infrastructure to support implementation.

While PGA is used as a common reference point for ease of understanding (which has always been the practice), all of the analysis done for the NEI White Paper used the entire spectral shape.

Comment/Question #4

Comment/Question #5 (1/3)

©2025 Nuclear Energy Institute 11 Please provide examples that show how the C10% criterion is applied at a cutset level, how a plant damage state is determined, and how the doses were calculated. The examples should also include evaluation of cli-edge eects.

This will be illustrated in the Tabletop.

The examples should include sensitivity studies considering various design options under the non-LLWR RIPB based seismic design.

We believe that the single design example in the Tabletop will be adequate to demonstrate the approach.

Comment/Question #6

A single scenario.

This will be demonstrated in the Tabletop.

Comment/Question #7

ANL_NSE-21-56 does not actually propose an approach, but rather investigates using a PRA-based margin assessment for the purpose of determining the challenges, opportunities, and next steps.

ANL and NEI have been exchanging information, and the NEI White Paper was one input to ANL_NSE-24-42, the next steps from ANL_NSE-21-56 are currently in draft.

ANL_NSE-24-42 proposes to use the same 2 x GMRS and C10% as its check on cliff-edge effect. This is the base case for the NEI White Paper, which has then a further, stricter cliff-edge check.

Difference is that ANL_NSE-24-42 is intended to develop plant-level safety insights per Part 53; the NEI White Paper is intended to identify the single scenario required for EPZ determination.

Comment/Question #8

NuScale considers their approach to be proprietary and has chosen not to make it available to NEI or other industry organizations.

As a note, we expect that the NuScale approach (while it could probably be adapted to other designs in some way) was designed specifically for use with that design. The NEI White Paper is intended to be technology neutral with regard to any light-water or non-light-water SMR.

Comment/Question #9

The NEI White Paper is not a stand-alone document for compliance with 10 CFR 50.160. The result is simply one input into the overall risk-informed, performance-based approach to emergency planning described in NEI 24-05.

The white paper is limited to describing the approach to defining the seismic scenario and plant damage state to be used in the overall assessment (i.e., it feeds into Chapter 4, Section 4.3.4, of NEI 24-05 as an Alternative Hazard Event).

All other interfaces with the rule are handled identically to the other EPZ scenarios as described in NEI 24-05.

Comment/Question #10

The approach in the NEI White Paper is only for the purpose of determining the boundary of the EPZ.

The need for changes would be addressed in accordance with Section 5.1 of NEI 24-05, Maintenance of Performance -

50.160(b)(1)(i).

Comment/Question #11

Discussion

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