ML24348A050
| ML24348A050 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/13/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| Shared Package | |
| ML24348A006 | List:
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| References | |
| LO-176318 | |
| Download: ML24348A050 (1) | |
Text
Response to NuScale Topical Report Audit Question Question Number: A-NonLOCA.LTR-35 Receipt Date: 04/29/2024 Question:
Clarify how the addition of boron baskets, venturis to the RVVs and RRVs, and/or removal of the IABs from RVVs impact the NRELAP5 models for the Non-LOCA events as identified in Section 6.
Currently, the models are similar to models for Rev 3. The staff notes that significant design changes exist between the NPM-20 and NPM-160; Rev. 3 of this TR is developed for NPM-160. (( 2(a),(c) Please provide proposed markups to the TR.
Response
The boron baskets, reactor vent valves (RVVs) and associated components, and reactor recirculation valves (RRVs) and associated components, are features that only perform a function during emergency core cooling system (ECCS) operation. Analysis of Chapter 15 events that include ECCS operation is outside the scope of the non-loss-of-coolant accident (non-LOCA) topical report and is performed using other methodologies as described in Section 1.2 of the non-LOCA topical report. Therefore, the performance of these features is not relevant to the non-LOCA topical report. The boron baskets role in reactivity control is addressed in the extended passive cooling and reactivity control methodology (XPC) topical report. The non-LOCA topical report provides an appropriate cross-reference (i.e., Reference 26) to the XPC topical report for this reason. The venturis in the RVVs and RRVs are valve internal components, and therefore only have an impact when the valves are open. Events where RVVs and RRVs open, either as the initiating event or as part of ECCS actuation in response to the initiating event, are addressed in the NuScale Nonproprietary NuScale Nonproprietary
LOCA topical report, with long-term ECCS cooling addressed separately in the XPC topical report. The non-LOCA topical report provides appropriate cross-references to the LOCA topical report and XPC topical report for this reason (i.e., References 2 and 26, respectively). ((
}}2(a),(c)
The modeling of the containment vessel is described in Section 6.1.7 and shown in Figure 6-16 of the non-LOCA topical report. ((
}}2(a),(c)
The containment volume is an input parameter ((
}}2(a),(c) The containment volume for the NPM-160 is used for analysis of the NPM-160. Likewise, the containment volume for the NPM-20 is used for analysis of the NPM-20. The impact of the NPM-20 design features (different from NPM-160) identified in the audit question on the containment volume is small relative to the total containment volume. In addition, the containment volume has minimal impact on non-LOCA events in the Final Safety Analysis Report (FSAR) Chapter 15. The non-LOCA events where containment volume may be relevant are those that may credit the high containment pressure signal: steam line breaks inside containment (FSAR Section 15.1.5), loss of containment vacuum and containment flooding (FSAR Section 15.1.6), and feedwater line breaks inside containment (FSAR Section 15.2.8).
For the double-ended guillotine steam line and feedwater line breaks inside containment, the pressurization of the containment is rapid and results in immediate reactor trip (i.e., within the first few seconds), demonstrating that the results are insensitive to small changes in containment volume. For the loss of containment vacuum and containment flooding, most cases, including the limiting case presented in FSAR Section 15.1.6, do not result in the high containment pressure signal being reached, demonstrating that the results are also insensitive to small changes in containment volume. Therefore, containment volume is not a key parameter for non-LOCA analysis and small changes in volume due to the design features described in this audit question, from whether explicitly accounting for them or not, have no impact. Note that containment volume is a more important consideration when determining peak containment pressure and temperature ((
}}2(a),(c) This consideration is outside the scope of the non-LOCA topical report.
NuScale Nonproprietary NuScale Nonproprietary
Because the NPM-20-specific design features identified in the audit question do not function during non-LOCA analysis and their impact on containment volume as an input parameter is minimal, the features do no impact the evaluation model described in the non-LOCA topical report. No markups are required. No changes to the SDAA are necessary. NuScale Nonproprietary NuScale Nonproprietary}}