ML25083A090
| ML25083A090 | |
| Person / Time | |
|---|---|
| Site: | Westinghouse |
| Issue date: | 03/24/2025 |
| From: | Ekaterina Lenning Licensing Processes Branch |
| To: | Westinghouse |
| References | |
| WCAP-16747-NP, Rev. 2, WCAP-16747-P, Rev. 2 | |
| Download: ML25083A090 (1) | |
Text
1 REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION TOPICAL REPORT WCAP-16747-P/NP, APPENDICES C AND D, REVISION 2, POLCA-T: SYSTEM ANALYSIS CODE WITH THREE-DIMENSIONAL CORE MODEL, APPENDICES C AND D WESTINGHOUSE ELECTRIC COMPANY DOCKET NO. 99902038 ISSUE DATE: 03/24/2025
Background
Westinghouse Electric Company (Westinghouse) submitted Topical Report (TR) WCAP-16747-P/NP, Appendices C and D, Revision 2, POLCA-T: System Analysis Code with Three-Dimensional Core Model, Appendices C and D (Agencywide Documents Access and Management System (ADAMS) Package Accession No. ML24267A194) for U.S. Nuclear Regulatory Commission (NRC) staff review and approval. The NRC issued an acceptance for review letter dated September 25, 2024 (ADAMS Accession No. ML24267A286). The NRC staff conducted a regulatory audit on November 19-21, 2024, based on the audit plan (ADAMS Accession No. ML24290A033), to increase efficiency in the review and the development of the NRC staffs safety evaluation (SE).
Regulatory Basis This review is an extension of the original approval of the POLCA-T code (ADAMS Accession No. ML102770087). The intent of the original application was to review the POLCA-T methodology in terms of its generic capabilities and to specifically review the methodology to analyze control rod drop accidents to demonstrate compliance with general design criteria (GDC) 28, Reactivity Limits, and to evaluate boiling water reactor (BWR) stability to demonstrate compliance with GDC 10, Reactor Design, and GDC 12, Suppression of Reactor Power Oscillations. The intent of the current application is to review the POLCA-T methodology in terms of its capability to analyze anticipated operation occurrence (AOO) transient analysis and anticipated transient without scram (ATWS) analysis to demonstrative compliance with GDC 10 and GDC 20, Protection System Functions. The applicable regulations are as follows:
Section 50.34 of Title 10 of the Code of Federal Regulations (10 CFR) Contents of construction permit and operating license application; technical information, requires that the licensee (or vendors) provide safety analysis reports to the NRC detailing the performance of systems, structures, and components provided for the prevention or mitigation of potential accidents.
Regulation 10 CFR Part 50, Appendix A, GDC 10, Reactor Design, requires that the reactor core and associated coolant, control, and protection systems shall be designed with appropriate margin to assure that specified acceptable fuel design limits are not exceeded during any condition of normal operation, including the effects of anticipated operational occurrences.
Regulation 10 CFR Part 50, Appendix A, GDC 12, Suppression of Reactor Power Oscillations, requires that the reactor core and associated coolant, control, and protection systems shall be designed to assure that power oscillations which can result in conditions exceeding specified acceptable fuel design limits are not possible or can be reliably and readily detected and suppressed.
2 Regulation 10 CFR Part 50, Appendix A, GDC 20, Protection System Functions, requires that the protection system shall be designed (1) to initiate automatically the operation of appropriate systems including the reactivity control systems, to assure that specified acceptable fuel design limits are not exceeded as a result of AOOs and (2) to sense accident conditions and to initiate the operation of systems and components important to safety.
Regulation 10 CFR Part 50, Appendix A, GDC 28, Reactivity Limits, requires that reactivity control systems shall be designed with appropriate limits on the rate of reactivity insertion considering a potential rod dropout event.
Additionally, the original approval of the POLCA-T code anticipated this further application and provided a list of necessary information in Appendix D of the SE. Many of the requests of additional information (RAIs) are focused on the requests that were previously identified as necessary information.
RAI 12-1 The NRC staff has previously assessed the validation of critical power ratio (CPR) correlations to predict transient behavior for [
] and is in the process of assessing [ ] Please confirm that those validations were performed with POLCA-T or, if they were performed with another code, please provide references to the same analysis performed with the other code.
RAI 12-2
[
]
RAI 12-3 Under Extended Power Uprate (EPU)/Maximum Extended Load Line Limit Analysis Plus (MELLLA+) conditions, the core outlet quality exceeds 20 percent. Additionally, fouling may degrade the steam separator performance. Both the impacts of high outlet quality and fouling need to be addressed before approval in transient applications. Please provide justification for the steam separator model capability to address these phenomena for EPU/MELLLA+
RAI 12-4 Provide an analysis of the bypass void formation on the simulated local power range monitor to ensure that the influence of bypass void formation is appropriately modeled in the development of [ ] Additionally, address how the [
] is kept within the same range of the original plant design or within the same range provided by the current legacy fuel [ ]
3 RAI 12-5 Please confirm that concerns as discussed in the Appendix D of the original NRC staffs SE related to the reactor internal pump model are only relevant to the Advanced BWR, which is outside the scope of the requested review.
RAI 12-6 Please provide justification for the use of [ ] for AOO transient and ATWS applications for application to mixed cores as well as application to [ ] As part of this discussion, please clarify the level of fidelity that will be used [
] and the acceptability of this modeling approach for the specified application.
RAI 12-7
[
]
RAI 12-8 Please provide justification that [ ] is appropriate for application of POLCA-T to AOO transients and ATWS. Please include justification that [
] are adequately captured for these events, and that [ ] is suitable for predicting unstable reactor behavior during ATWS instability (ATWS-I).
RAI 12-9 Please provide justification for the adequacy of the [
] in POLCA-T.
RAI 12-10 Please provide details on the application [ ] in POLCA-T utilized in evaluation of AOO transients and ATWS. Specifically, please address how [
] are treated.
RAI 12-11 Please provide justification for the use of [ ] Additionally, please describe and justify [
]
Also, please provide the following additional information on the [ ] oscillating flow tests that are discussed in Section C.3.1.4 of TR WCAP-16747-P, Appendix C:
- 1. Figures C.3-8 through C.3-10 provide [
] In order to assess [
] predicted by POLCA-T during the oscillations, please provide [
] calculated by POLCA-T.
4
- 2. Please also provide the elevation(s) at which [ ] oscillating flow tests and compare this to POLCA-T.
- 3. Please provide justification that [ ]
oscillating flow tests, [ ] provide adequate validation for expected conditions during ATWS-I.
- 4. If the POLCA-T models are relying on [ ] please provide validation of those models, specifically under failure to [ ]
RAI 12-12 Please confirm that the application of POLCA-T to Delta CPR Versus Oscillation Magnitude (DIVOM) analysis is outside the scope of this review.
RAI 12-13 Please provide details of [ ] for POLCA-T, including a specification and justification of the models used, given that [ ] for ATWS events may reach [ ] at which [ ] becomes significant.
RAI 12-14 Is [ ] required for AOO transient or ATWS analysis? If so, please provide justification on the treatment of uncertainties in this model.
RAI 12-15 Much of the POLCA-T methodology for AOO transient and ATWS analysis relies on the Phenomena Identification and Ranking Table (PIRT) and other information provided in the NRC-approved TR WCAP-17203-P-A, Fast Transient and ATWS Methodology. However, POLCA-Ts application to [ ] is not directly addressed in the current TR. Please provide justification for POLCA-Ts application to [ ]
RAI 12-16 Please clarify the intent of the Appendix C discussion regarding the interface to the plant control simulation tool SAFIR when the use of SAFIR was previously approved in the initial review of POLCA-T.
RAI 12-17
[
]
RAI 12-18 Please discuss whether [ ] been validated and describe how this validation was performed.
RAI 12-19 Please confirm that Sections C.4, C.6, D.4, and D.6 are providing a description of the approved uncertainty quantification methodology for the fast transient analysis and ATWS, not requesting approval of any new methodology aspects not previously reviewed and approved in TR WCAP-17203-P-A.
5 RAI 12-20 Please provide justification for the application of POLCA-T to ATWS instability. Provide POLCA-T demonstration results for a representative limiting ATWS-I event, which demonstrate the ability of POLCA-T to predict the following phenomena:
- 5. Dryout that advances beyond cyclic dryout-rewet behavior into failure-to-rewet conditions, resulting in elevated peak cladding temperature;
- 6. Inlet flow reversal and predicted fluid mass and energy exchange with the inlet plenum;
- 7. Dryout and post-dryout heat transfer behavior during liquid and/or vapor flow reversal within the channel; and
- 8. Ability to capture ATWS-I relevant downcomer effects including the impact of water level reduction on core inlet subcooling.
- 9. Provide additional details on the measured and calculated oscillations during the
[ ] fine motion control rod drive event, including the oscillation mode (in-phase or out-of-phase) and whether dryout was predicted.
- 10. Discuss the analysis that licensees will be expected to perform for ATWS-I events, and which figure(s) of merit will be used to demonstrate acceptable performance.
RAI 12-21 Please clarify the role of the decay ratio and oscillation frequency calculation within the ATWS instability methodology. Is this calculation performed for informational purposes, or does it impact the ATWS instability evaluation process or its conclusions?
Concurred via email OFFICE NRR/DORL/LLPB/
PM NRR/DORL/LLPB/
BC NRR/DORL/LLPB/
LA*
NRR/DSS/SFNB/
BC NAME ELenning JRankin DHarrison SKrepel DATE 03/24/2025 03/24/2025 03/20/2025 03/14/2025