ML20044D532
| ML20044D532 | |
| Person / Time | |
|---|---|
| Issue date: | 02/13/2020 |
| From: | Jose March-Leuba Advisory Committee on Reactor Safeguards |
| To: | Matthew Sunseri Advisory Committee on Reactor Safeguards |
| Wang, W, ACRS | |
| Shared Package | |
| ML20044D595 | List: |
| References | |
| Download: ML20044D532 (4) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION ADVISORY COMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, DC 20555 - 0001 February 13, 2020 MEMORANDUM TO:
Matthew W. Sunseri, Chairman Advisory Committee on Reactor Safeguards FROM:
Jose March-Leuba /RA/
Advisory Committee on Reactor Safeguards
SUBJECT:
PROPOSED RECOMMENDATION FOR ACRS REVIEW OF NUSCALE POWER, LLC, DESIGN CERTIFICATION APPLICATION - SAFETY EVALUATION WITH NO OPEN ITEMS FOR CHAPTER 15, TRANSIENT AND ACCIDENT ANALYSES In response to the Committees request, I have reviewed the NRC staffs safety evaluation report (SER) with no open items for Chapter 15, Transient and Accident Analyses, dated January 28, 2020 (ML20028D595). The following is my recommended course of action concerning further review of this chapter of the design certification application and the staffs associated safety evaluation.
SER Phase 4 Summary Chapter 15 of the SER documents the staffs review of Revision 3 of Chapter 15, Transient and Accident Analyses, of the NuScale Design Certification Application, Part 2, Tier 2 c (ML19241A398). The SER summarizes the staffs safety review of the NuScale design against the requirements of 10 CFR 52, Subpart B.
Chapter 15 of the applicants final safety analysis report documents the applicants analyses of anticipated operational occurrences, infrequent events, and postulated accidents organized based on the eleven major classes of events defined in the Standard Review Plan (SRP),
labeled 15.0 through 15.10. The Phase 4 staff SER reviews these events and concludes that the NuScale design accident analysis satisfies all applicable regulations.
Applicable Concerns from ACRS Phase 3 Letter Report We reviewed the Phase 2 Chapter 15 SER and wrote an interim letter on August 2, 2019, that concluded our Phase 3 review. This letter addresses Chapters 3, 6, 15, and 20 together. With respect to Chapter 15, our main Phase 3 recommendation was:
NuScales power module (NPM) can experience a return-to-power under accident analysis assumptions but does not violate any specified acceptable fuel design limits.
This potential operational condition should be precluded in the long term.
The Phase 2 SER had 31 unique open items, of which 11 were unresolved issues without a clearly defined, mutually understood path towards resolution at Phase 2. We conducted our interim review with all open items, but noted that:
The final status of the review is based on resolution of these unresolved issues, as well as the remaining open items.
Staff Response to ACRS Letter Report The staff response to our Phase 3 August 2, 2019, letter states:
With regard to the Chapter 15 return-to-power analyses, whether caused by a stuck rod or non-uniform boron distribution, the NRC staffs review considered the relevant figure of merit to be the specified acceptable fuel design limits, consistent with SECY-18-0099, NuScale Power Exemption Request from 10 CFR Part 50, Appendix A, General Design Criterion, 27, Combined Reactivity Control Systems Capability, dated October 9, 2018 (ADAMS Accession No. ML18065A431). The staff is still reviewing these analyses. The staff agrees that the NuScale boron addition systems could be used to eventually bring the reactor to a subcritical state as a longer-term coping strategy. However, in SECY-18-0099, the NRC staff did not identify subcriticality as a required criterion in the longer term for the NuScale design. Although NuScale has not identified the use of a boron addition system to ensure long-term subcriticality, nonsafety-related systems relied on during the first 7 days following a design-basis event are subject to special regulatory treatment consistent with the provisions outlined in SECY-96-128, Policy and Key Technical Issues Pertaining to the Westinghouse AP600 Standardized Passive Reactor Design, dated June 12, 1996 (ADAMS Accession No. ML003708224), and its associated staff requirements memorandum, dated January 15, 1997. The staff is still reviewing the need for boron addition within the first 7 days following a design-basis event for the NuScale design.
With respect to your observations regarding the acceptance criteria for anticipated operational occurrences and postulated accidents for the NuScale design, the NRC staff notes that NuScales licensing approach is consistent with its request for exemption from General Design Criterion 27, Combined Reactivity Control Systems Capability, of Appendix A, General Design Criteria for Nuclear Power Plants, to 10 CFR Part 50, Domestic licensing of production and utilization facilities. NuScale has recently clarified its proposed licensing basis by revising DCA, Tier 2, Section 3.1.3.8, Criterion 27-Combined Reactivity Control Systems Capability, to state that fuel cladding integrity is maintained for all design basis events, including postulated accidents, such that the effect of a postulated return to power with failed fuel has not been evaluated in the analysis of accident consequences. Therefore, to preclude unanalyzed accident consequences, NuScales design basis prohibits fuel failures under postulated accident conditions.
Open Items from Phase 3 Requiring Further ACRS Review The Phase 2 SER had 31 unique open items referred in the text in multiple locations. Many of them were related to documentation or ongoing reviews that were not finished at the time.
However, 11 of the 31 were unresolved issues without a clearly defined, mutually understood path towards resolution at Phase 3.
The Phase 4 SER has resolved all these 31 open items. However, the SER does not contain the details of how the items were resolved, only summary statements are provided. Some of the resolutions are based on converting the open items to confirmatory items where the activity is scheduled to be completed soon, but is still under final review, like issuing the final methodology SERs.
Recommendation As lead reviewer for NuScale Chapter 15, I recommend that the Committee perform additional Phase 5 review of this chapter and schedule a staff presentation on the resolution of the 11 previously unresolved issues. Specifically, we would like in-depth presentations on:
Long term cooling, and duration requirements Return to power Boron redistribution under emergency core cooling system (ECCS) operation Changes to Chapter 15 analysis in Phase 4 safety analysis report, including o ECCS design o Changes in actuation logic variables and setpoints o Changes in instrumentation (e.g. level range in containment)
Changes to loss-of-coolant accident analyses in Phase 4, including o Inadvertent opening of an RPV valve results o Changes to inadvertent actuation block actuation range o Impact on peak containment pressure (short description)
Chapter 15 analyses that change significantly from Phase 2 to Phase 4 or didnt change after significant model changes Downcomer boron dilution event Chapter 19 anticipated transient without scram scenario. Does downcomer boron dilution affect it?
February 13, 2020
SUBJECT:
PROPOSED RECOMMENDATION FOR ACRS REVIEW OF NUSCALE POWER, LLC, DESIGN CERTIFICATION APPLICATION - SAFETY EVALUATION WITH NO OPEN ITEMS FOR CHAPTER 15, TRANSIENT AND ACCIDENT ANALYSES Package No.: ML20044D595 Accession No: ML20044D532 Publicly Available Y Sensitive N Viewing Rights:
NRC Users or ACRS Only or See Restricted distribution *via email OFFICE ACRS/TSB SUNSI Review ACRS/TSB ACRS NAME WWang WWang LBurkhart (KHoward for)
WKirchner (KHoward for)
DATE 2/13/2020 2/13/2020 2/13/2020 2/13/2020 OFFICIAL RECORD COPY