ML25017A201
| ML25017A201 | |
| Person / Time | |
|---|---|
| Issue date: | 01/15/2025 |
| From: | Vivanco R NRC/NRR/DNRL/NRLB |
| To: | |
| References | |
| Download: ML25017A201 (2) | |
Text
1 Supplement - ACRS - Loss-of-Coolant Accident Evaluation Methodology Topical Report Review Presentation - Closed Session, January 15, 2025 The staff is providing this supplement to highlight differences between the draft Advance Safety Evaluation Report (ASER) for NuScale, LLC. Topical Report "Loss-of-Coolant Accident Evaluation Model," TR-0516-49422, Revision 3 that was submitted to the Advisory Committee for Reactor Safeguards (ACRS) for review on December 14, 2024 and the version that was published on January 7, 2025 (ML24312A002). These differences do not change any of the staffs conclusions. The staffs presentation during the January 15, 2025 ACRS subcommittees closed session accurately reflected the staffs conclusions in the published version of the ASER.
In summary, the differences include editorial changes, clarifications, and refinement of language in the limitations and conditions. The technical differences are the inclusion of additional supporting evidence of the staffs conclusions, specifically for scaling analysis of the LOCA EM, N-RELAP5 code version use, and containment response analysis methodology (CRAM). The changes are mainly due to additional information submitted by the applicant that supported the staffs conclusions in the draft ASER.
The table below lists the SE sections where changes were made, summary of the changes,
and the slide number where this information was presented during the January 15, 2025, closed subcommittee meeting:
SER Section Summary of Change Presented on Slide #
Section 4.4.2, Phenomenon Identification and Ranking Table Rankings As a result of additional information submitted by NuScale and confirmatory analysis performed by the staff, the staff found the existing PIRT for the in-vessel flow and heat transfer is not impacted by the generation and transport of the small amount of radiolytic gas.
14 Section 4.5.1.5, Helical Coil Steam Generators (HCSG)
The staff confirmed that the DHRS modeling and coupled pool nodalization is sufficient to model the overall decay heat removal responses and heat transfer capability.
15 Section 4.5.1.6, Containment Vessel and Reactor Pool The staff confirmed that the uncertainty in natural convection heat transfer modeling from the CNV and DHRS to the pool due to thermal stratification would not be safety-significant with respect to the containment pressurization and DHRS capacity.
29 Section 4.6, NRELAP Computer Code The staff confirmed code update and basemodel version-to-version benchmark results and determined that the code version update and model changes are acceptable and consistent with this NPM methodology.
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2 SER Section Summary of Change Presented on Slide #
Section 4.7.5.1, Test Facility The staff confirmed, based on the results of the various assessment sensitivity studies, the applicants conclusion that the NRELAP5 model responses are consistent with physics-based expected results and that there are very negligible effects on the event FOMs.
11-12 Section 4.8.2.7,
((
))
The staff confirmed that heat transfer from the lower head to the reactor pool has a minor impact on the CNV pressure response and that using the ((
)) for modeling heat transfer from the lower hemispherical CNV head does not have any safety-significance with respect to the CNV T/H response.
29 From Section 4.8.3.2.4, Reactor Coolant System Depressurization Scaling The staff confirmed ((
)) and conservatism.
Therefore, the conclusion in the distortion analysis is acceptable.
12 Section 4.8.3.3, Assessment of NuScale Facility Integral Effect Test Data The staff confirmed that the applicants extensive assessments in the LTR with these NIST-2 tests, and the code-to-data agreement is excellent for the figures of merit.
12 Section 4.8.3.4, Evaluation of NuScale Integral Effect Tests Distortions and NRELAP5 Scalability As a result of additional analysis and justification provided by the applicant, the staff confirmed that NIST-2 chronology scaling is maintained as it was in the NIST-1 scaling.
11 Section 7. Limitation and Condition Section 4.5.2, Analysis Setpoints and Trips.
L/C modified to include unless the method is followed that is described in section 5.2 of the LOCA EM TR that models the riser level instrument setpoint based on mixture level in the riser, using one of the approaches described in detail in section 5.2 (not including the application - specific alternate approach). (This addition is also reflected in Section 4.5.2.). Additionally, L/C #4 and #9 were combined into one L/C.
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