ML19224B115

Response to NRC Follow-Up Question PRA RAI 03, License Amendment Request - LAR-16-01490 NFPA 805 Program Revisions

ML19224B115
Person / Time
Site:	Summer
Issue date:	08/12/2019
From:	Lippard G Dominion Energy Co, South Carolina Electric & Gas Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
19-339, LAR-16-01490
Download: ML19224B115 (5)

Text

V. C. Summer Nuclear Station Bradham Blvd & Hwy 215, Jenkinsville, SC 29065 ~ Dominion Mailing Address P.O. Box 88, Jenkinsville, SC 29065 August 12, 2019  ::;iiiii" Energy Dominion Energy.com Document Control Desk Serial No.19-339 U.S. Nuclear Regulatory Commission VCS-LIC/BJD RO Washington , DC 20555 Docket No. 50-395 License No. NPF-12 SOUTH CAROLINA ELECTRIC & GAS COMPANY VIRGIL C. SUMMER NUCLEAR STATION (VCSNS) UNIT 1 LICENSE AMENDMENT REQUEST- LAR-16-01490 NFPA 805 PROGRAM REVISIONS RESPONSE TO NRC FOLLOW-UP QUESTION PRA RAI 03 By letter dated August 29, 2018 (Agencywide Document Access and Management System (ADAMS) Package Accession No. ML18242A658), South Carolina Electric and Gas (SCE&G) ,

submitted a license amendment request (LAR) for the Virgil C. Summer Nuclear Station, Unit 1 (VCSNS) , to make changes to its approved Fire Protection Program (FPP) under 10 CFR 50.48(c). By email dated June 27, 2019 {ML19179A126), the Nuclear Regulatory Commission (NRC) staff provided a follow-up request for additional information (RAI) to PRA RAI 03. This follow-up RAI provided two options for response , Option (i) and Option (ii). During a July 23, 2019 public teleconference with the NRC, SCE&G indicated its intention to respond to Option (ii) and the NRC staff verbally communicated several additional requests for information related to this option . The NRC provided an e-mail on July 30 , 2019 which included the supplemental information that the staff requested during the phone call.

The VCSNS actions to support the response to Follow-Up Question PRA RAI 03 is provided in the attachment to this letter.

Should you have any questions: please call Mr. Michael Moore at (803) 345-4752.

I declare under penalty of perjury that the foregoing is true and correct. ~

,r//.z/(f Executed on  ?

~ Gee 4 A. Lippard Site Vice President V.C . Summer Nuclear Station Commitments contained in this letter: VCSNS will subm it the updated response to PRA RAI 03 by October 11 , 2019.

Attachment:

VCSNS Response to NRC Follow-Up Question PRA RAI 03 cc: G. J . Lindamood - Santee Cooper L. Dudes- NRC Region 11 S. A. Williams - NRC Project Mgr.

NRC Resident Inspector A. Nair-Gimmi - SCDHEC In a letter dated July 30, 2019, South Carolina Electric & Gas Company (SCE&G) requested a License Amendment to amend the VC Summer operating license to reflect the name change from SCE&G to Dominion Energy South Carolina (DESC) . The amendment request is currently under review by the NRC.

Serial No.19-339 Attachment ATTACH MENT LAR-16 -01490- NFPA 805 Program Revisio ns Respon se to NRC Follow- Up Questio n PRA RAI 03 Virgil C. Summe r Nuclear Station - Unit 1 South Carolina Electric and Gas

Serial No.19-339 Attachment LICENSE AMEND MENT REQUEST LAR-16-01490 NFPA 805 PROGR AM REVISIONS RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION VIRGIL C. SUMME R NUCLEA R STATION UNIT 1 NRC Comment:

By letter dated August 29, 2018 (Agencywide Documen t Access and Management System (ADAMS) Package Accession No. ML18242A657), and supplemented by letters dated April 29, 2019 (ADAMS Accession No. ML19119A365) and May 22, 2019 (ADAMS Accessio n No.

ML19150A696), South Carolina Electric and Gas (SCE&G) submitted a license amendm ent request (LAR) for the Virgil C. Summer Nuclear Station, Unit 1 (VCSNS), to make changes to its approved fire protection program (FPP) under 10 CFR 50.48(c). In its LAR, the licensee proposed to make several changes to its FPP including changes to plant modifications, use of performance-based alternatives to the requirem ents of NFPA 805, Chapter 3, and several clarifications and editorial corrections.

Based on the information in the suppleme nt dated May 22, 2019, on June 27, 2019 (ADAMS Accession No. ML19179A126), the U.S. Nuclear Regulato ry Commission (NRG) issued a follow-up Request for Additional Information (RA/) to PRA RA/ 03.

On July 23, 2019, a public teleconference was held between SCE&G and NRG staff to discuss SCE&G's proposed response to the June 27, 2019, RA/ to PRA RA/ 03. During the teleconference, SCE&G stated they propose to utilize option (ii) of the June 27, 2019, RA/.

Based on the discussion during the teleconference, the NRG staff is providing further clarification to PRA RA/ 03, option (ii), below.

Follow-Up Question Probabilistic Risk Assess ment (PRA), Request for Additional Information (RAil 03 (Issued on June 27, 2019]:

Section 2.4.3.3 of NFPA 805 states that the probabili stic risk assessment (PRA) approach, methods, and data shall be acceptable to the NRG. Section 2.4.4.1 of NFPA 805 further states that the change in public health risk arising from transition from the current fire protection program to an NFPA 805 based program, and all future plant changes to the program, shall be acceptable to the NRG.

In the letter dated May 22, 2019, the licensee responde d to PRA Request for Additiona l Information (RA/) 03 and stated, in part:

The longer the seals can withstand loss of seal cooling, the more time is available for operators to trip the RCPs [reactor coolant pumps], and the lower the failure probabili ty of that action. Dynamic loss-of-seal-cooling tests of N-9000 RCP seals have shown that RCPs can operate in excess of 60 minutes with no measurable change in seal leakage.

. . . The Human Reliability Analysis (HRA) that supports the 2018 VCSNS FPRA [fire Page 1 of 3

Serial No.19-339 Attachment PRAJ models a 60-minute system time window for the operator action to trip RCPs. The 60-minute system time window is retained in the current FPRA.

In the safety evaluation associated with Amendme nt No. 199, dated February 11, 2015 (ADAMS Accession No. ML14287A289), the NRG staff found acceptable the licensee's N-9000 RCP seal failure model applied in the FPRA, which is based on the RCP seal failure model and associated failure probabilitie s used in WCAP-161 75-A, "Model for Failure of RCP Seals Given Loss of Seal Cooling in CE NSSS Plants" (ADAMS Accession No. ML071130383). WCAP-16175-A indicates that the N-9000 RCP seals have been designed to survive 30 minutes of continued RCP operation without RCP seal cooling. Also, the response to RA/ 1. 15. 1 documente d in WCAP-16175-A states, "[a]s data for RCP seal operation without seal cooling for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> is not available, this event will be redefined to require tripping the RCP within 20 minutes." Therefore, it appears that the licensee's use of a 60-minute system time window for operator action to trip RCPs in the FPRA to support the LAR dated August 29, 2018 is not consistent with that used in the NRG-acce pted RCP seal model (i.e., FPRA RCP seal failure model accepted in the safety evaluation associated with Amendme nt No. 199, which is based on WCAP-16175-A). Also, the basis for using the 60-minute system time window provided in the response to PRA RA/ 03 is unclear to the NRG staff.

(i) Provide the technical basis for use of a 60-minute system time window for operator action to trip RCPs without seal cooling for the N-9000 RCP seals installed at VCSNS. If results of any tests or performanc e data are used to support this basis, discuss these results and data, including how this information is used to substantiat e the 60-minute system time window and is applicable for the VCSNS RCP seal design and operating conditions that can affect seal performance. Also discuss the sensitivity of the risk results to the system time window for operator action to trip RCPs (e.g., compare the total risk and change-in-risk of using a 60-minute system time window with that used in the FPRA RCP seal failure model accepted in the safety evaluation associated with Amendme nt No. 199). OR (ii) Alternative ly to part (i), provide updated risk results in Table PRA RA/ 03-1 of letter dated May 22, 2019 that uses the system time window for operator action to trip RCPs based on the FPRA RCP seal failure model accepted in the safety evaluation associated with Amendmen t No. 199, and discuss how the updated risk results align with the risk acceptance guidelines of Regulatory Guide 1.205. Propose a mechanism that ensures an NRG-accep ted RCP seal failure model is used in the FPRA for self-approv al of post-transition changes.

Supplemen t to Option (ii) {based on July 23, 2019, teleconfere nce discussion ]:

Describe in sufficient detail any additional changes to the VCSNS PRA models (i.e., internal events, internal flooding, seismic, and fire) in support of the updated risk results that were not described in the LAR dated August 29, 2018, as supplemen ted by letters dated April 29, 2019 and May 22, 2019.

Explain and justify whether the changes are PRA maintenan ce or PRA upgrades as defined in ASMEIANS RA-Sa-2009, Section 1-5.4, as qualified by Regulatory Guide 1.200, Revision 2.

For all PRA changes that constitute a PRA upgrade, state if a peer review has been performed for any PRA upgrades in accordance with an NRG-acce pted process. As applicable, provide the open facts and observation s (F&Os) characteriz ed as findings associated with this peer Page 2 of 3

Serial No.19-339 Attachment review and explain how the F&Os were dispositioned to Capability Category II for this application.

If a peer review was not performed for PRA upgrades, propose a license condition such that prior to implementing self-approval of post-NFPA-805 transition changes:

• PRA upgrades will be appropriately peer reviewed and any finding-level F&Os are closed in accordance with an NRG-accepted process (e.g., focused-scope peer review, F&O closure review, direct submittal to the NRG), and,

• Confirm that the updated transition change-in-risk estimates for this application align with the risk acceptance guidelines of Regulatory Guide 1.205.

SCE&G Response:

SCE&G will complete the following actions to support a response to Option (ii) of the PRA RAI 03 for resolution of the Reactor Coolant Pump (RCP) seal modeling issue. These activities will result in PRA refinements, procedure revisions, and Operations training. Upon completion of these activities, a response to Option (ii) including the requested supplemental information will be submitted to the NRC by October 11, 2019.

1. Incorporation of Refueling Water Storage Tank (RWST) depletion timing into the timeline for loss of seal injection and the time available for tripping the RCPs for accident sequences involving loss of RCP seal cooling due to RWST draindown. The baseline evaluation assumed that RWST draindown instantaneously resulted in the loss of all seal injection. The RWST depletion analysis provides as-built, as-operated time estimates.

2. Refinement of fire scenario progression to provide a more realistic characterization of target damage over time. This includes refined and focused fire modeling target identification and refinement of fire-induced damage states.

3. PRA model refinements and detailed circuit analysis to reduce conservatism in cable mapping and to incorporate appropriate NUREG-7150, Volume 2 hot-short induced spurious operation probabilities. Additional circuit analysis and reviews have also been performed to ensure the availability of power supplies to support RCP thermal barrier cooling.

4. Refinement of conservative operator action timelines associated with actions in the main control room to trip RCPs and local actions to trip RCPs manually. No additional or new Recovery Actions are expected.

Other refinements may also be implemented as part of the effort. Since the July 23, 2019 teleconference discussion, considerable progress has been made in reducing risk values in the Fire PRA Model. Completion of the actions described above will ensure the Fire PRA Model aligns with the risk acceptance guidelines of Regulatory Guide 1.205 and Regulatory Guide 1.174.

Risk results provided in Attachments of the August 29, 2018 (ML18242A657) and May 22, 2019 (ML19150A696) correspondence will be superseded by the October 11, 2019 submittal.

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