ML17111A893

Response to Request for Additional Information Regarding Mitigating Strategies Assessment (MSA) Report for Flooding

ML17111A893
Person / Time
Site:	Surry
Issue date:	04/13/2017
From:	Stoddard D Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
17-148
Download: ML17111A893 (5)

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VIRGINIA ELECTRIC ANO POWER COMPANY RICHMOND, VIRGINIA 23261 April 13, 2017 U.S. Nuclear Regulatory Commission Serial No.17-148 Attention: Document Control Desk NRA/WDC RO Washington, DC 20555 Docket Nos. 50-280/281 License Nos. DPR-32/37 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

SURRY POWER STATION UNITS 1AND2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING MITIGATING STRATEGIES ASSESSMENT (MSA) REPORT FOR FLOODING In a letter dated January 27, 2017 (Serial No.16-480), Virginia Electric and Power Company (Dominion) submitted the flooding Mitigating Strategies Assessment (MSA)

Report for Surry Power Station Units 1 and 2. In an email dated March 13, 2017, the Nuclear Regulatory Commission (NRC) transmitted a request for additional information (RAI) to Dominion related to the MSA. Dominion agreed to respond to the RAI by April 18, 2017.

The attachment to this letter provides Dominion's response to the NRC's RAI.

If you have any questions regarding this information, please contact Gary Miller at (804) 273-2771.

Sincerely, Daniel G. Stoddard Senior Vice President and Chief Nuclear Officer COMMONWEALTH OF VIRGINIA COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Daniel G. Stoddard, who is Senior Vice President and Chief Nuclear Officer of Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that company, and that the statements in the document are true to the best of his knowledge and belief.

Acknowledged before me this \~'\4- day of _ _,_A_~F--'--'*

=---* 2017.

My Commission Expires:

Serial No.17-148 Docket Nos. 50-280/281 Page 2 of 2 Commitments made in this letter: No new regulatory commitments Attachments:

1. Response to Request for Additional Information Regarding Mitigating Strategies Assessment Report for Flooding, Surry Power Station cc: U.S. Nuclear Regulatory Commission, Region II Regional Administrator Marquis One Tower 245 Peachtree Center Ave. NE Suite 1200 Atlanta, Georgia 30303-1257 K. R. Cotton Gross Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 G-9A 11555 Rockville Pike Rockville, MD 20852-2738

8. L. Mozafari Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 H-12 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Surry Power Station J. E. Reasor, Jr.

Old Dominion Electric Cooperative Innsbrook Corporate Center, Suite 300 4201 Dominion Blvd.

Glen Allen, Virginia 23060

Serial No.17-148 Docket Nos. 50-280/281 ATTACHMENT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING MITIGATING STRATEGIES ASSESSMENT REPORT FOR FLOODING VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

SURRY POWER STATION UNITS 1 AND 2

Serial No.17-148 Docket Nos. 50-280/281 Attachment, Page 1 of 2 In a letter dated January 27, 2017, Virginia Electric and Power Company (Dominion) submitted the flooding Mitigating Strategies Assessment Report (MSA) for Surry Power Station Units 1 and 2. In an email dated March 13, 2017, the Nuclear Regulatory Commission (NRC) transmitted a request for additional information (RAI) to Dominion related to the MSA.

RAl-1 In both the LIP and intake canal failure flood hazard, the Emergency Switchgear room could be flooded. Please explain how the electrical strategy (for Phases 1, 2, and 3) is still valid with the re-evaluated flood that results in switchgear being flooded. In particular, please address the "alternative strategies" referenced on page 3 and 12, as it is not evident what those alternative strategies are.

Dominion Response Either the reevaluated local intense precipitation (LIP) flood hazard or the reevaluated intake canal failure flood hazard could result in flooding of the Emergency Switchgear Room (ESGR) . (including the battery rooms), which would render the AC and DC emergency electrical power distribution system unavailable. However, alternative mitigating strategies are available to provide the required Phase 1, 2 and 3 FLEX mitigating strategy functions that are impacted by an ESGR flood.

Phase 1 Alternative Strategies - Obtaining Kev Plant Parameters Phase 1, 2, and 3 FLEX mitigating strategies use key instrumentation powered from the emergency power distribution system for display in the Main Control Room (MCR). As an alternative mitigating strategy, the necessary Phase 1, 2 and 3 key plant parameters used by the FLEX mitigating strategies are displayed at the Remote Monitoring Panel, whose power cabling does not route through the ESGR (FLEX Support Guideline 1/2-FSG-7). The Remote Monitoring Panel is located in the Cable Spreading Room, elevation 42 feet mean sea level, and is not susceptible to any reevaluated flood hazard. The Remote Monitoring Panel is powered by an uninterruptible power source with 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> capability and is repowered within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> by a small portable generator.

A station procedure provides an additional defense-in-depth alternative strategy for manually obtaining FLEX key plant parameters locally.

Phase 2 Alternative Strategies - Closing SI Accumulator Isolation MOVs and Repowering MCR Lighting and ESGR Lighting and Receptacles Alternative FLEX mitigating strategies are available in lieu of the FLEX mitigating strategy functions provided by installed plant equipment powered by the Phase 2 portable 480 VAC, 120/240 VAC, and National SAFER Response Center (NSRC) 4160 VAC generators, collectively known as BOB generators.

Serial No.17-148 Docket Nos. 50-280/281 Attachment, Page 2 of 2 Closing the safety injection (SI) accumulator isolation motor-operated valves (MOVs) prior to a second reactor coolant system (RCS) cooldown eliminates an adverse impact on RCS natural circulation by preventing nitrogen injection into the RCS during the cooldown. However, a second RCS cooldown is not a FLEX mitigating strategy timeline required function. An alternative strategy to closing the SI accumulator isolation MOVs is provided in FLEX Support Guideline 1/2-FSG-10, which includes direction for manually venting nitrogen from the SI accumulators in preparation for a second RCS cooldown.

The alternative strategy for repowering lighting in the MCR and ESGR following an extended loss of AC power (ELAP) event is the use of Appendix R lighting and supplemental lighting. The MCR and ESGR are equipped with Appendix R lighting units having a battery design life of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. In addition, supplemental lightiQg sources (e. g., rechargeable Pelican suitcase remote area lighting systems, head lamps and flashlights, etc.) are available in the Beyond Design Basis (BOB) Storage Building and MCR as alternative sources of lighting. The Appendix R lighting units and the various supplemental lighting sources are available as the long-term lighting alternative.

Alternative lighting and repowering receptacles in the ESGR are unnecessary if the ESGR is flooded.

Phase 3 Alternative Strategies - Containment Cooling Options The containment design parameters are not expected to be challenged for several (> 7) days following an ELAP event. An alternative mitigating strategy option for Phase 3 containment cooling is a variation of the containment spray FLEX mitigating strategy option provided in FLEX Support Guideline 1/2-FSG-12. Various portable BOB and NSRC pumps can provide Service Water (SW) to the Recirculation Spray Heat Exchangers (RSHXs), and provide Refueling Water Storage Tank (RWST) or fresh water through the containment spray (CS) system spray headers to fill the containment sump. After sufficient volume is in the sump, long-term containment cooling requires starting the Outside Recirculation Spray (ORS) pumps. This long-term containment cooling option is viable if the ORS pumps can be repowered. Seven days is considered adequate time for the Corporate Emergency Response Center (CERC) to develop and implement direct powering of the ORS pumps.

Another variation of the containment spray FLEX mitigating strategy option is also available as an alternate mitigating strategy option for Phase 3 containment cooling.

Since the ELAP containment heat loads are small relative to design heat loads, the CERC could direct the containment sump to be filled in batches such that the process of filling the sump could effectively cool the containment for longer than seven days without repowering the ORS pumps for RSHX cooling.

Therefore, both of these variations of the containment spray FLEX mitigating strategy option are viable Phase 3 alternative containment cooling mitigating strategy options.