ML19053A520

OEDO-19-00135 - Supplemental Response to the Advisory Committee on Reactor Safeguards Letter, Response to the December 15, 2016, Staff Letter Regarding Draft Final Rule on Mitigation of Beyond-Design-Basis Events and Associated Regulatory G

ML19053A520
Person / Time
Issue date:	04/09/2019
From:	Neih H Office of Nuclear Reactor Regulation
To:	Riccardella P Advisory Committee on Reactor Safeguards
Bernardo R, NRR/DLP, 301-415-2621
Shared Package
ML19053A532	List: ML19053A520 ML19053A529
References
LTR-17-0075-1, OEDO-19-00135
Download: ML19053A520 (4)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 9, 2019 Dr. Peter Riccardella, Chairman Advisory Committee on Reactor Safeguards U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

SUBJECT:

SUPPLEMENTAL RESPONSE TO THE ADVISORY COMMITTEE ON REACTOR SAFEGUARDS LETTER, RESPONSE TO THE DECEMBER 15, 2016, STAFF LETTER REGARDING DRAFT FINAL RULE ON MITIGATION OF BEYOND-DESIGN-BASIS EVENTS AND ASSOCIATED REGULATORY GUIDANCE, DATED FEBRUARY 14, 2017

Dear Dr. Riccardella:

The purpose of this letter is to update the Advisory Committee on Reactor Safeguards (ACRS) on staff activities related to seismic probabilistic risk assessment (SPRA) reports, given recent Commission direction on the draft final rule on mitigation of beyond-design-basis events (MBDBE). As you are aware, the ACRS provided invaluable insights and support to the staff in developing the draft MBDBE rule, as detailed in Dr. Bleys letters dated December 6, 2016 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML16341B371), and February 14, 2017 (ADAMS Accession No. ML17045A206). The staff addressed the ACRS recommendations in letters dated December 15, 2016 (ADAMS Accession No. ML16343A146), and March 17, 2017 (ADAMS Accession No. ML17058A229).

This letter provides the ACRS with an update on recent staff activities and includes references to four publicly available SPRA reports and corresponding U.S. Nuclear Regulatory Commission (NRC) staff assessments. Given recent Commission direction, the staff is providing this letter in lieu of conducting previously scheduled briefings.

In Dr. Bleys February 14, 2017, letter, he noted that the ACRS would appreciate briefings on the staffs reviews of the seismic risk assessments for two or three sites at which the reevaluated ground motion response exceeds the current safe shutdown earthquake by more than a factor of two in the 1 to 10 Hertz frequency range (i.e., sites that will be required to perform an SPRA). In the staffs response on March 17, 2017, we stated that the staff anticipates receiving all seismic assessments by the end of calendar year 2019 and that the staff will coordinate briefings with the ACRS on our review of the requested SPRAs. Since March 2017, the amount of NRC staff and resources assigned to post-Fukushima lessons learned activities has steadily declined, based on a projected workload that aligned with the staffs proposed draft final MBDBE rule. With the recent Commission decision modifying the final MBDBE rule (see the Affirmation Notice and Staff Requirements Memorandum dated January 24, 2019 (ADAMS Accession No. ML19023A038)), we now face an anticipated increased workload to complete the activities necessary to finalize and implement the rulemaking.

P. Ricardella It is through this lens of increased workload and diminishing staff resources that the staff re-looked at the underlying issue for the requested full-day ACRS briefing. We understand that the ACRSs original interest was the proposed screening criteria to be used in relation to the seismic mitigation strategies assessments (MSA) for Path 51 sites. In Dr. Bleys December 6, 2016, letter, the ACRS recommended that the NRC staff omit the overall seismic risk screening criteria of 5 x 10-5 seismic core damage frequency and 5 x 10-6 large early release frequency specified in appendix H, Section 4.5.3 of Nuclear Energy Institute guidance document NEI 12-06, Diverse and Flexible Coping Strategies (FLEX) Implementation Guide (ADAMS Accession No. ML16354B421). The staffs December 15, 2016, response noted that the results of the SPRA will be reviewed for potential cost-justified, substantial safety enhancements, beyond those which will be required by the draft final MBDBE rulemaking; and that the staff did not intend to revise the guidance to remove the overall risk screening criteria. In light of the Commissions decision that the consideration of the reevaluated hazards within the mitigation strategies will not be a regulatory requirement in the MBDBE rule, we believe that there is no longer a difference of opinion between the ACRS and NRC staff regarding the seismic screening criteria for Path 5 seismic MSAs.

Although the staff no longer intends to provide briefings on the reviews of the seismic risk assessments, the staff appreciates the previous interactions with the ACRS on this matter and is providing the enclosed listing of the publicly available SPRA reports and staff assessments completed to date, with the corresponding ADAMS accession numbers. Since the Commission has communicated that the majority of benefits of the reviews have already been realized, the staff is providing this listing of reports and assessments as an alternative to the briefings committed to under different circumstances. Consistent with Commission direction in SRM-SECY-16-0142, Final Rule: Mitigation of Beyond-Design-Basis Events (ADAMS Accession No. ML19023A038), the staff intends to expeditiously close the remaining post-Fukushima activities and no further interaction with the ACRS is anticipated on these issues.

1 Path 5 refers to the process to be used to evaluate the mitigation strategies developed under Order EA-12-049, Mitigation Strategies, at sites where the re-evaluated ground motion response exceeds the current safe shutdown earthquake by more than a factor of two in the 1 to 10 Hertz frequency range.

P. Ricardella The decision to provide the publicly available SPRA information in lieu of a full-day briefing was discussed by the Director, Division of Licensing Projects, and the Executive Director, ACRS.

The staff looks forward to interactions with the ACRS on other regulatory issues. If you have any questions, please contact Brett Titus at 301-415-3075 or Brett.Titus@nrc.gov.

Sincerely,

/RA Michele Evans for/

Ho K. Nieh, Director Office of Nuclear Reactor Regulation

Enclosure:

Listing of Publicly Available SPRA Reports and Staff Assessments cc: Chairman Svinicki Commissioner Baran Commissioner Burns Commissioner Caputo Commissioner Wright SECY

Package ML19053A532; Letter ML19053A520; Enclosure ML19053A529 *concurred via e-mail NRR-106 OFFICE NRR/DLP/PBMB NRR/DLP/PBMB/LA* NRR/DLP/PBMB/BC(A) NRR/DLP/D NAME RBernardo SLent BTitus LLund DATE 2/21/19 2/21/19 2/27/19 3/12/19 OFFICE NRR/D NAME HNieh (MEvans for)

DATE 4/9/19