ML25014A271
| ML25014A271 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 01/13/2025 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25013A204 | List: |
| References | |
| LO-178078, LO-177590 | |
| Download: ML25014A271 (1) | |
Text
Response to NuScale Topical Report Audit Question Question Number: A-NonLOCA.LTR-46S Receipt Date: 08/09/2024 Question:
Audit question A-NonLOCA.LTR-46 was received by NuScale on June 24, 2024. NuScale provided a response on July 22, 2024. On August 9, 2024, NuScale received the following written feedback from the NRC:
(( 2(a),(c) However, the LTR does not define clear criteria to show how these determinations are made in accordance with the evaluation model. For figures of merit associated with the non-LOCA topical report, identify the thresholds that determine whether margins to acceptance criteria are sufficient and the thresholds that determine whether figures of merit are insensitive to biases, initial conditions and analysis assumptions. (( }} 2(a),(c) It is unclear to NRC staff whether these additional sensitivity studies (i.e., sensitivity studies not indicated by event-specific tables) are requirements of the evaluation model and, if so, what indicates that additional sensitivity studies are required. Clarify whether and in what circumstances sensitivity studies beyond those indicated in event-specific "initial conditions, biases, and conservatisms" tables are required by the non-LOCA LTR evaluation model. Provide LTR markup as needed. NuScale Nonproprietary NuScale Nonproprietary
Response
This response is a supplement to the July 22, 2024 response to address the feedback from August 9, 2024; the July 22, 2024 response remains unchanged in the electronic reading room (eRR). The context of the original audit question is provided: (( }}2(a),(c) The original audit question requested that NuScale demonstrate that this basis is acceptable. NuScale has demonstrated the basis for the statement in TR-0516-49416-P, Revision 4. (( }}2(a),(c) Specifically, the operation of the reactor safety valve (RSV) at its biased high setpoint effectively determines the peak RCS pressure. This technical basis was added to TR-0516-49416-P, Revision 4 as indicated in the markup in the original response. To address the additional NRC feedback, each aspect of the feedback is addressed by providing the text of the feedback in indented, italicized text, followed by the NuScale response in un-indented, regular text. ((
}}2(a),(c) However, the key technical basis for the conclusion, as specified in the markups provided with the original audit response, is that the RSV lift limits the pressurization of the RCS. The RSV design ensures that the NuScale Nonproprietary NuScale Nonproprietary
maximum RCS pressure does not significantly exceed the RSV lift setpoint. Modification of initial and boundary conditions in the calculations can generate many cases with similar maximum RCS pressure due to this design feature. However, the LTR does not define clear criteria to show how these determinations are made in accordance with the evaluation model. For figures of merit associated with the non-LOCA topical report, identify the thresholds that determine whether margins to acceptance criteria are sufficient and the thresholds that determine whether figures of merit are insensitive to biases, initial conditions and analysis assumptions. Based on this NRC feedback, NuScale concludes that the NRC feedback is concerned about how insensitivity will be judged in the future. The NRC feedback requests additional specific detailed information be added to TR-0516-49416-P to determine the size of the change relative to the margin that can be considered insensitive. NuScale believes this is unnecessary. This level of detail was not necessary in the previous revision of the NRC-approved topical report. ((
}}2(a),(c) The NRC feedback now requests specific detailed information be added to TR-0516-49416-P to determine the size of the change relative to the margin that can be considered insensitive. NuScale believes this is unnecessary because the insensitivity of the results can be shown regardless of the margin. (( }}2(a),(c)
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(( }}2(a),(c) As described in TR-0516-49416-P, and the associated markups in the original response, it is a characteristic of the design of the NuScale Power Module (NPM) that peak RCS pressure does not challenge acceptance criteria. The peak pressures for the heatup events were summarized in Table 1 of the original response. It is worth noting that the peak RCS pressures (ranging from 2310 to 2320 psia) are slightly above the nominal setpoint for opening of the second reactor safety valve (RSV) (2290 psid per Final Safety Analysis Report Table 5.2-2). (( }}2(a),(c) It is unclear to NRC staff whether these additional sensitivity studies (i.e., sensitivity studies not indicated by event-specific tables) are requirements of the evaluation model and, if so, what indicates that additional sensitivity studies are required. Clarify whether and in what circumstances sensitivity studies beyond those indicated in event-specific "initial conditions, biases, and conservatisms" tables are required by the non-LOCA LTR evaluation model. The sensitivity studies performed on (( }}2(a),(c) are in addition to those required by TR-0516-49416-P, Revision 4, Non-Loss-of-Coolant Accident Analysis Methodology. These sensitivity studies are not part of the implementation of the methodology in TR-0516-49416-P. The additional sensitivity studies are studies included at the discretion of the analyst for information. It is acceptable for an implementing analysis to perform additional sensitivity studies or include additional information beyond what is required by the methodology. Because inclusion of any such additional studies or information is, by definition, beyond the scope of the methodology, additional information on this decision-making process is not included in TR-0516-49416-P. Provide LTR markup as needed. NuScale Nonproprietary NuScale Nonproprietary
There are no additional markups to TR-0516-49416-P as a result of this supplemental response. No changes to the SDAA are necessary. NuScale Nonproprietary NuScale Nonproprietary}}