ML24347A149

Preliminary Observations Comments Questions on NEI EPZ White Paper 14 Nov 2024

ML24347A149
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Issue date:	11/14/2024
From:	Sosa B Office of Nuclear Reactor Regulation
To:	Austgen K Nuclear Energy Institute
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pg. 1 14 Nov 2024 Preliminary Observations, Comments, and Questions on NEI White Paper: Selection of a Seismic Scenario for an EPZ Boundary Determination This paper presents preliminary observations, comments, and questions on Nuclear Energy Institute (NEI) White paper on Emergency Planning Zone (EPZ) and NRC stas earlier observations provided at the December 7, 2023, public meeting for discussions with the NEI industry experts that developed the paper. It is anticipated that additional questions may arise as the sta continue to review the paper and supporting material.

Some Observations on NEI Approach:

The stated goal of the White Paper is to develop a framework for selecting a seismic scenario for use in determining the EPZ. The approach utilizes insights from past seismic probabilistic risk assessments (SPRAs) and other relevant engineering sources. Based on our understanding of the White Paper, these are the key assumptions:

1. A site-speci"c Ground Motion response Spectra (GMRS) is available.

2. Although, if SPRA is not available, a PRA-based seismic margin study is available.

3. Although, not explicitly stated, the approach is discussed in context of a standard design having a Certi"ed Seismic Design Response Spectra (CSDRS) and a seismic margin study that includes fragilities.

Comments and questions are organized along the following four components of the approach.

1. Selection of a Beyond Design Basis Earthquake (BDBE) for scenario development:

Insights from recent (post-Fukushima SPRAs) are used for this purpose, particularly the relationships between core damage High Con"dence Low Probability of Failure (HCLPFs) and a site-speci"c GMRSs are investigated. The 2 x Ground Motion Response Spectra (GMRS) is chosen to develop the scenario. An upper bound cuto with a Peak Ground Acceleration (PGA) = 1.0 g is also proposed.

2. Seismic Scenario: The earthquake response spectra based on 2 x GMRS is used to determine failure of speci"c SSCs using the criterion described below.

3. Fragility evaluation:C10% capacity of a Structure, System, or Component (SSC) is used to determine failure or a success of that component. If the C10% capacity is less than 2 x GMRS, a failure is assumed. If it exceeds 2 x GMRS, complete success is assumed. The basis for this come from NEI 12-06, which used parts of this methodology (use of C10%) to evaluate FLEX coping capacity for beyond Design Basis Earthquake (DBE) events. A cli-edge check is also evaluated.

pg. 2 14 Nov 2024

4. Consequence Calculation: The dose consequence calculations include both source term and atmospheric eects, i.e., a Level 3 SPRA event sequences. Results of these calculations are used to de"ne the EPZ.

It appears that there are three of implicit and explicit assumptions that are critical components that must be available to apply the methodology:

1. An existing site-speci"c GMRS that is based on RG 1.208, assuming ASCE 43 Seismic Design Category 5 (SDC-5) design levels.

2. SSCs that are designed to same criteria as those used for large light water reactors (LLWR) design.

3. An existing seismic PRA or a seismic margin model for the Level 3 SPRA including fragility information Comments and Questions:

1. The proposed approach seems to indicate the availability of a Level-3 plant model that can be used for seismic margin study. It also implies that SSCs are designed in sucient detail to allow estimate for C10% capacity. It is very likely that for site-speci"c CP applications under Part 50, this information (Level-3 PRA and C10% capacity) will not be available. Please discuss how the proposed approach in the White Paper can be implemented at the CP stage.

2. The proposed approach assumes that the SSCs for new applications will be designed using design codes that are used for LLWR design based on SDC-5 loads. However, it seems likely that new non-LLWRs will include safety signi"cant SSCs that are designed using both nuclear and non-nuclear codes and standards and using dierent SDCs.

Please discuss the applicability of the proposed approach in terms of i) appropriateness of C10% criterion (2 x GMRS), and ii) the assumption that any SSC that has C10% capacity greater than 2 x GMRS is considered fully successful. Also, discuss how cli-edge eects will be determined under these circumstances.

3. There is an implicit assumption in the White Paper that the site-speci"c GMRS is the ASCE 43 SDC-5 GMRS. This assumption needs to be explicitly stated., i.e., that the SDC-5 GMRS is to be used regardless of possible lower SDC level SSCs and the possible use of commercial design codes.

4. 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.

pg. 3 14 Nov 2024

5. The core damage HCLPFs from recent LLWR SPRAs are used to understand the relationship between the GMRS and HCLPF. Why werent the Large Early Release Frequency (LERF) HCLPFs not considered for application of the whitepaper? It seems to us that the LERF HCLPF maybe a more appropriate surrogate for consequences considering the fact the many new non LLWR designs may not have a physical containment. Please provide the HCLPF data for LERF for the plants studied.

6. The description of how the source term and the scenario earthquake are developed is not clear. 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. The examples should include sensitivity studies considering various design options under the non-LLWR RIPB based seismic design.

7. Please clarify whether the application of the approach in the White Paper results in a single scenario failure or if there are multiple failure scenarios.

8. The proposed approach in the ANL report, Regulatory Treatment of Low Frequency External Events under a Risk-Informed Performance-base Licensing Pathway, describes use of seismic margin information from LLWRs to evaluate potential high-consequence releases associated with low annual exceedance frequency external events, such as those that result from large, rare earthquakes. This approach is currently under review by NRC. Although, the EPZ application is somewhat dierent from the high-consequence low-probability events, we note that there needs to be some consistency between two approaches. For example, in the ANL approach, the consequences are determined using SPRA models and fragilities as they are. Thus, there could be more than one high-consequence sequence that leads to release. Please discuss whether your suggested scenario approach will always bound the results from the ANL approach.

9. Please discuss how this approach diers from that was used in the recently approved NuScale design certi"cation.

NRC questions and observations that were provided at the public meeting (December 7,2023).

Need additional discussion and detail in several areas discussed on the following slides Future submittal would bene"t from a demonstration/tabletop to help the sta understand the implementation of the proposed methodology (Included in question 6)

The proposal is silent on how the source term will be determined from or assigned to the single BDB seismic sequence. (Included in question 6 above)

pg. 4 14 Nov 2024 It is unclear how the result will be used to compare against criteria in 10 CFR 50.160 and how the methodology interfaces with the remainder of the rule.

NEI should address how potential cli edge eects would be handled. (Included in question 6 above)

NEI should address how changes in the facility during the life of the plant would be addressed to assess any changes needed to the emergency plan.

How does this proposed approach coordinate with other ongoing activities regarding low frequency hazards for design and EPZ sizing for non-LWRs using LMP? (Included in question 8 above)