ML24228A211
| ML24228A211 | |
| Person / Time | |
|---|---|
| Site: | 99902049 |
| Issue date: | 08/15/2024 |
| From: | Carolyn Lauron NRC/NRR/DNRL/NLIB |
| To: | Brenner A Holtec, SMR |
| References | |
| Download: ML24228A211 (1) | |
Text
From:
Carolyn Lauron To:
Andrew Brenner Cc:
Michelle Hayes; India Banks; Manny Sayoc; Monica Haneman; Clark Shurtleff
Subject:
NRC Staff Response to SMR (Holtec) Question re: 10 CFR 50.155 and Regulatory Treatment of Non-Safety Systems (RTNSS) (Project 99902049)
Date:
Thursday, August 15, 2024 1:42:00 PM Attachments:
SMR-300 Clarification Question - 10CFR50-155_RTNSS.pdf Hi Andrew -
Please find the NRC staff response below to the question posed in the attached document emailed to me on May 22, 2024.
The attached document and this email will be placed in ADAMS and made publicly available.
- Thanks, Carolyn
NRC Staff Response:
Consistent with SECY 94-084, the passive system design basis is 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. For passive designs, typically, safety-related systems automatically establish and maintain safe-shutdown conditions for the plant following design-basis events, including an extended loss of ac power source for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, assuming the most limiting single failure and no operator actions. Typically, no installed non-safety-related SSCs are relied upon to meet the requirements of 10CFR50.63 (Station Blackout Rule) which is part of RTNSS Criterion A.
After 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, support actions and equipment may be needed to maintain safe shutdown for 7days in a passive design. As discussed in SECY-96-128, Policy and Key Technical Issues Pertaining to the Westinghouse AP600 Standardized Passive Reactor Design, dated June12,1996 and the associated Staff Requirements Memoranda, the Commission approved the staff's position that the site be capable of sustaining design basis events with onsite equipment and supplies for the long term, with replenishment of consumables (such as diesel fuel oil) from offsite suppliers after seven days. (Reference 1)
As discussed in SECY 96-128, the staff further stated that the equipment needed for post 72hour support need not be in automatic standby mode, but must be readily available for connection and protected from natural phenomena, including seismic events, as required by Appendix A to 10 CFR Part 50, General Design Criteria (GDC) 2, Design Basis for Protection Against Natural Phenomena. The SSCs needed to maintain safe-shutdown post 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> up to 7 days in passive designs including following seismic events are evaluated under RTNSS Criterion B and are considered risk significant.
Mitigation of Beyond-Design-Basis Events rule, 10 CFR 50.155 requires:
(1) response to a beyond-design basis external event (BDBEE), assuming a loss of all alternating current (AC) power event concurrent with a loss of normal access to the normal heat sink (LNHS), as required by 10 CFR 50.155(b)(1),
(2) capability to respond to a loss of a large plant area due to explosions or fire (LOLA),
as required by 10 CFR 50.155(b)(2),
(3) protection of equipment associated with mitigation of a BDBEE, as required by 10 CFR 50.155(c),
(4) training requirements as defined by 10 CFR 50.155(d),
(5) spent fuel pool monitoring as required by 10 CFR 50.155(e).
For those designs that do not rely on safety-related SCCs to perform long-term safety functions, passive design features and risk significant SSCs used to meet RTNSS Criterion B may be used to meet the requirements of 10 CFR 50.155. This mitigation capability is augmented by specific site characteristics that are unique and must be addressed by an applicant or licensee. Specific guidance for meeting 10 CFR 50.155 can be found in Regulatory Guide1.226 Revision0, dated June 2019, Flexible Mitigation Strategies For Beyond-Design-Basis Events. (Reference 2)