ML24348A045
| ML24348A045 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/13/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24348A006 | List:
|
| References | |
| LO-176318 | |
| Download: ML24348A045 (1) | |
Text
Response to NuScale Topical Report Audit Question Question Number: A-NonLOCA.LTR-33 Receipt Date: 04/29/2024 Question:
Provide methodology for performing sensitivity studies on the impacts of the axial power shape primary and secondary system pressure, flow and fluid temperature responses.
Section 4.3.1.1.2 states: Sensitivity studies on the axial power shape confirm that the primary and secondary system pressure, flow and fluid temperature responses are not significantly affected by the axial power shape. Therefore, use of a nominal center-peaked average axial power shape input is appropriate for the system transient analyses. These statements indicate that sensitivity studies are used to determine the impacts of the axial power shape on primary and secondary system pressure, flow and fluid temperature responses. However, the TR does not provide information on what sensitivities need to be performed and the methods for performing these sensitivity studies and the acceptance criteria.
Please provide proposed markups to the TR to include this information.
Response
The discussion of axial power shape in Section 4.3.1.1.2 in the current revision of the non-loss-of-coolant accident (non-LOCA) topical report (TR-0516-49416-P, Revision 4) is identical to the discussion in Revision 3 of the non-LOCA topical report that was previously reviewed and approved by the NRC (other than an editorial change to add a reference to the subchannel topical report supplement).
As stated in Section 3.4.3.1 of the safety evaluation report (SER) for Revision 3 of the non-LOCA topical report:
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TR Section 4.3.1.1.2, Axial Power Shape, states that sensitivity studies on the axial power shape, confirm that the primary and secondary system pressure, flow, and fluid temperature responses are not significantly affected by the axial power shape; therefore, the NRELAP5 non-LOCA system transient analyses use a nominal center-peaked average axial power shape. The NRC staff notes that a top-peaked axial power shape is typically limiting. Therefore, the NRC staff audited calculations to confirm that RCS and secondary pressures are insensitive to power shape, as discussed in the associated audit report (ML19039A090). The NRC staff concludes that the audited sensitivity studies adequately support the docketed information and finds the use of a nominal center-peaked average axial power shape for the NRELAP5 non-LOCA system transient analyses acceptable. The NRC staff further notes that the applicant applied the most limiting axial power shape when evaluating SAFDLs in the downstream subchannel analysis.
Based on the applicability review demonstrating the similarity between the NuScale Power Module (NPM) for the US460 design (i.e., NPM-20) and the NPM for the US600 design (i.e.,
NPM-160), no changes were made to the methodology for the axial power shape and sensitivity studies on the axial power shape were not repeated.
Because (1) the treatment of axial power shape has not changed since the prior NRC approval, (2) the NRC previously audited the axial power shape sensitivity studies, and (3) no new sensitivity studies have been performed, there is no reason to provide further information about the topic. No markup is provided because the level of information in Revision 4 of the topical report is consistent with what was sufficient for prior NRC approval of Revision 3.
No changes to the SDAA are necessary.
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