ML20049D685
| ML20049D685 | |
| Person / Time | |
|---|---|
| Issue date: | 02/18/2020 |
| From: | Rempe J Advisory Committee on Reactor Safeguards |
| To: | Matthew Sunseri Advisory Committee on Reactor Safeguards |
| Widmayer, D, ACRS | |
| Shared Package | |
| ML20044D595 | List: |
| References | |
| Download: ML20049D685 (3) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION ADVISORY COMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, DC 20555 - 0001 February 18, 2020 MEMORANDUM TO: Matthew W. Sunseri, Chairman Advisory Committee on Reactor Safeguards FROM: Joy Rempe, Member /RA/
NuScale Subcommittee 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 20, MITIGATION OF BEYOND-DESIGN-BASIS EVENTS In response to the Committees request, I reviewed the NRC staffs safety evaluation with no open items for Chapter 20, Mitigation of Beyond-Design-Basis Events (MBDBEs),
December 5, 2019 (ML19338B783). The memorandum provides my recommended course of action concerning further review of this chapter of the design certification application (DCA) and the associated staff safety evaluation report (SER).
SER Phase 4 Summary Chapter 20 of the SER documents the staff review of Rev. 3 of Chapter 20, Mitigation of Beyond-Design-Basis Events, of the NuScale DCA, Part 2, Tier 2 Final Safety Analysis Report (FSAR). In this chapter of the FSAR, NuScale describes responses of their design to the assumed damage state of a beyond-design-basis event in an extended loss of alternating current power and loss of normal access to the normal heat sink [as required by 10 CFR 50.155(b)(1)], and to a loss of large area due to explosion or fire [as required by in 10 CFR 50.155(b)(2)]. Design certification applicants can defer all MBDBE requirements to the combined license applicant. However, NuScale is voluntarily seeking NRC approval for its strategies to meet these requirements in the DCA.
In reviewing Chapter 20, the staff applied the approach outlined in SECY-19-0066, Staff Review of NuScale Powers Mitigation Strategy, for Beyond-Design-Basis External Events.
The staff verified that the design capacities and capabilities of permanently-installed structures, systems, and components can provide adequate cooling for the core, containment isolation and heat removal, spent fuel pool (SFP) cooling, and SFP level instrumentation for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
Consistent with the review approach applied for operating reactors and a prior DCA, the staff did not review design feature capacity and capability beyond 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following a beyond-design-basis external event (BDBEE). No Open Items were identified in the Phase 4 version of the SER for this chapter.
M. Sunseri Concerns from ACRS Phase 3 Letter Report We did not make any recommendations or conclusions specific to Chapter 20 in our interim Phase 3 letter report on Chapters 3, 6, 15, and 20. However, we observed that two open items precluded the staff from making a safety finding with respect to 10 CFR 50.155 requirements -
the mechanisms responsible for the predicted flow fluctuations associated with decay heat removal system (DHRS) operation and the potential for recriticality due to boron redistribution.
As part of their Phase 4 review, staff conducted an audit of documents related to the calculations supporting the NuScale station blackout transient during the first 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The staff points toward analysis results presented in DCA Section 5.4.3 for DHRS thermal-hydraulic performance, including the potential for reactor coolant system natural circulation oscillations and toward Chapter 15.0.6 analyses to assess the potential for and effects of boron dilution.
These results allowed the staff to conclude that the applicants design and approach to maintain core cooling has sufficient capacity and capability for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> using installed equipment.
During my review, I observed that Chapter 20 in Rev 3 of the DCA contains three tables without any explanatory information. These tables note that spent fuel pool water level data provide sufficient information to assure that required functions are maintained in the long-term.
However, these tables also indicate that several types of instrumentation data are required to assure establishment of the core cooling function (Table 20.1-1), containment isolation and heat removal (Table 20.1-2), and spent fuel cooling (Table 20.1-3). This appears inconsistent with statements in the DCA indicating that no instrumentation is required to establish these safety functions during such events. The staffs Phase 4 SER is silent on this inconsistency and lacks any explanatory information for these tables in Rev 3 of the DCA.
NRC Staff Response to ACRS Letter Report Not Applicable Open Items from Phase 3 Requiring Further ACRS Review None. Two open items were identified in the Chapter 20 Phase 2 review by the staff. In our Phase 3 review, we did not provide any recommendations or conclusions pertaining to Chapter 20. There are no unresolved items related to NuScale DCA Chapter 20 and the associated SER.
Recommendation I recommend that the Committee not perform any additional Phase 5 review of this chapter, contingent upon the staff briefing us about the apparent inconsistency associated with the DCA Chapter 20 tables and successful completion of our planned Chapter 15 and focus area reviews.
M. Sunseri February 18, 2020
SUBJECT:
PROPOSED RECOMMENDATION FOR ACRS REVIEW OF NUSCALE POWER, LLC, DESIGN CERTIFICATION APPLICATION - SAFETY EVALUATION WITH NO OPEN ITEMS FOR CHAPTER 20, MITIGATION OF BEYOND-DESIGN-BASIS EVENTS Package No.: ML20044D595 Accession No: ML20049D685 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 DWidmayer DWidmayer LBurkhart (CBrown for) WKirchner (CBrown for)
DATE 2/18/2020 2/18/2020 2/18/2020 2/18/2020 OFFICIAL RECORD COPY