ML20049A007
| ML20049A007 | |
| Person / Time | |
|---|---|
| Issue date: | 02/18/2020 |
| From: | Ballinger R Advisory Committee on Reactor Safeguards |
| To: | Matthew Sunseri Advisory Committee on Reactor Safeguards |
| Brown, C, ACRS | |
| Shared Package | |
| ML20044D595 | List: |
| References | |
| Download: ML20049A007 (4) | |
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:
Ronald Ballinger /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 4, REACTOR In response to the Committees request, I have reviewed the NRC staffs safety evaluation report (SER) with no open items for NuScale DCA Chapter 4, Reactor, dated January 16, 2019 (ML19336B593). 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 4 of the NuScale DCA describes the reactor and the reactor core design, the fuel rod and fuel assembly design, the core control and monitoring components, and the nuclear and thermal-hydraulic design. The fuel rod and fuel assembly design features, analyses and anticipated performance have been adapted from pressurized water reactor (PWR) fuel technology currently in-service in the operating fleet. The operational linear power levels are well below current designs, and fuel assembly limits are within the operating fleet experience.
Chapter 4 of the SER documents the staffs review of Revision 3 of Chapter 4, Reactor.
During the 663rd meeting of the Advisory Committee on Reactor Safeguards, May 2-3, 2019, we met with representatives of NuScale and the NRC staff to review Chapter 4, Reactor. Our NuScale Subcommittee also reviewed this chapter on April 17, 2019.
Applicable Concerns from ACRS Phase 3 Letter Reports Our Phase 3 Chapter 4 review identified open items that required Chapter 15 (transient accident analyses) to demonstrate acceptability of the NuScale reactor design in satisfying General Design Criterion (GDC) 27 (Combined Reactivity Control Systems Capability), GDC 34 (Residual Heat Removal) and GDC 35 (Emergency Core Cooling). We did not identify any additional issues at that time for Chapter 4, but we made the following observations:
The use of reduced-length commercial fuel under NuScale operating conditions offers larger margins than current PWRs. However, there were a number of open items
discussed in the Phase 2 SER related to the NuScale reactor design response to Anticipated Operational Occurrences (AOOs) and accidents, and whether the reactor design meets the requirements of GDC 27 Combined Reactivity Control Systems Capability and GDC 35 Emergency Core Cooling.
The staff has evaluated NuScales responses to RAIs concerning the ability of the reactor design to maintain long-term reactivity control following AOOs or postulated accidents. We recommended that Chapter 15 accident analysis issues needed to be reviewed and resolved to demonstrate acceptability of the NuScale reactor design in meeting GDC 27 and GDC 35.
In Chapter 4, NuScale chose to establish the shutdown margin based on normal operation conditions. However, following reactor shutdown, operators can control the cooldown of the reactor via feedwater control, or for some scenarios, may rely on passive Decay Heat Removal System (DHRS) cooling. DHRS operation results in a lower moderator temperature than manual operation using standard procedures.
Lower moderator temperatures may result in lower shutdown margins. We suggested that it would be prudent to evaluate long-term reactivity at the lower moderator temperatures resulting from DHRS operation as opposed to normal shutdown temperatures.
NuScale defines Operating Mode 4 (Transition) as that mode required prior to transport of the power module to the refueling station, and this transport operation may be an important contributor to risk. We suggested that it would be prudent to provide additional margin to criticality by specifying, in the core operating limits report, that the refueling-mode boron concentration be established before the reactor state is changed from Mode 3 (Safe Shutdown) to Mode 4.
Staff Response to ACRS Letter Report The NRC staff responded to our letter report as follows:
The NRC staff agreed with our conclusions and recommendations. As the NRC staff continues to engage the applicant to resolve the remaining open items related to the subject chapter and Chapter 15 accident analysis issues with regard to satisfying GDC 34, and GDC 35, in Appendix A, General Design Criteria for Nuclear Power Plants, to Title 10 of the Code of Federal Regulations (10 CFR)
Part 50, Domestic Licensing of Production and Utilization Facilities, the staff has a path forward to address all regulatory requirements and risk-significant items for the NuScale design.
The NRC staff continues to engage the applicant to resolve the remaining open items associated with the exemption to GDC 27.
Summary and Recommendations The Phase 4 SER closed 14 open items related to aspects of the reactor and Emergency Core Cooling System (ECCS) necessary to meet GDCs 17 (Electric Power System), 27, 34, and 35, items related to fuel assembly thermomechanical response to satisfy GDC 2 (Design Bases for Protection Against Natural Phenomena), or items related to the analysis of the
response of the core to postulated events analyzed in Chapter 15. Because many of these items relate to content found in Chapters 6 (Engineered Safety Features), 8 (Electric Power),
and 15, our concurrence is contingent on our review of those chapters and the focus area reviews related to boron dilution and return to criticality, ECCS system operation, and probabilistic risk assessment.
Our first three concerns have been resolved by the staff in the Phase 4 SER. We look forward to discussing the fourth concern as part of the Boron Dilution and Return to Criticality focus area.
As lead reviewer for NuScale Chapter 4, I recommend that the Committee not perform any additional Phase 5 review of this chapter.
February 18, 2020
Subject:
PROPOSED RECOMMENDATION FOR ACRS REVIEW OF NUSCALE POWER, LLC, DESIGN CERTIFICATION APPLICATION-SAFETY EVALUATION WITH NO OPEN ITEMS FOR CHAPTER 4, REACTOR Package No.: ML20044D595 Accession No: ML20049A007 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 CBrown CBrown LBurkhart (CBrown for)
WKirchner (CBrown for)
DATE 2/18/2020 2/18/2020 2/18/2020 2/18/2020 OFFICIAL RECORD COPY