ML102180072

North Anna Power Station, Units 1 & 2, Additional Clarification for Preacs

ML102180072
Person / Time
Site:	North Anna
Issue date:	07/07/2010
From:	Shaub T Dominion
To:	V Sreenivas Plant Licensing Branch II
Sreenivas V.NRR/DORL/LPL2-1 415-2597
References
Download: ML102180072 (1)

Text

From: Tom Shaub [tom.shaub@dom.com] Sent: Wednesday, July 07, 2010 3:35 PM To: Sreenivas, V

Subject:

additional clarification for PREACS V, In response to your e-mail NAPS is not experiencing any weather related problems at this time. Per your request here are the additional clarifications associated with the PREACS. Changes are identified in red. The OE response is new information.

Please call if you have any additional needs.

What is the difference in this leakage at fluid temperature assumed in a design basis accident? NAPS recognizes that ECCS leakage will be impacted by system parameter differences experienced during normal operating conditions and those experienced during a DBA. The North Anna ECCS Leakage Log, 1-LOG-20 and 2-LOG-20, accounts for the difference in leakage that could be expected if the ECCS system were in the recirculation mode following a DBA. NAPS defines this leakage as "Accident Leakage". Some sections of the systems see a greater pressure during post-LOCA time than during normal plant operations. For leaks in those areas, the leak value must be increased by a factor that accounts for the higher pressure during ECCS recirculation. The factor is the square root of the ratio of LHSI system pressure during recirculation to normal operating pressure at the leakage point. This conservatively equates to the square root of 160.8 (LHSI system pressure during recirculation) divided by 27 (lowest normal operating pressure at the suction of the Charging Pumps due to VCT pressure and weight of water due to height) which provides a conversion factor of 2.44. Only those leaks in the LHSI system from the discharge of the pumps to the LHSI containment penetrations and to the suctions of the Charging Pumps, including Charging Pump seal leakage, require this correction factor. This conversion to accident leakage is dependent on pressure and not fluid temperature.

HHSI pump seal vendor (Flowserve) Operating Experience?

North Anna, Diablo Canyon, and DC Cook have the same pump & seal combination. Flowserve did not find any issues with the seal at these utilities. However, a Flowserve Field Service Specialist went to North Anna to look at the charging pumps for leaking seals. This was to evaluate the leakage that was discussed in our April 8, 2010 letter (Serial No.10-207) regarding minor leakage when the pump is secured.

"On occasion, after a HHSI pump has been secured, traces of boric acid crystals may become lodged between the seal faces (micro-inches) when the seal faces cool. Consequently, some minor leakage may occur on the magnitude of a few drops per minute when the pump is secured. To date we have not seen any indication that a leaking seal in static condition will be degraded when the pump is running. In fact, static leakage usually goes to zero when the pump is started due to dynamic forces on the seal faces and the temperature increase between the seal faces to above the boric acid solubility curve."

What is the mission time for the HHSI pumps?

In support of our GSI-191 containment sump effort we analyzed the operation of the all ECCS pumps and seals for 30 days. In all instances the pumps and associated seals were capable of performing their safety function i.e., provide the required flow and limit leakage to acceptable levels. The evaluation for the HHSI pumps concluded that there would be no noticeable change in leak rates until at least 60% of the carbon ring nose is worn away. This ring is checked periodically (currently 5 years) to ensure adequate seal life (30 days of operation) during a DBA.

Although the mission time is 30 days for the HHSI pumps, in both SBLOCA and LBLOCA scenarios, the HHSI pumps would mostly likely not be run for 30 days.

For the SBLOCA the HHSI pumps would supply water until the plant is depressurized. This could include the use of the HHSI pump and LHSI pump in "piggyback" mode of operation if the plant is not depressurized before the RWST is emptied. However, plant procedures require an aggressive plant depressurization; the plant can be easily depressurized within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and the HHSI pumps would no longer be necessary to provide core cooling.

For the LBLOCA the HHSI and LHSI pumps start and run on the SI. Both the HHSI and LHSI will continue to run through the injection phase into the recirculation phase (several hours). At that point core cooling is maintained by the flow from one HHSI and LHSI. If RCS pressure is low, one LHSI pump is sufficient to maintain adequate recirculation flow and cooling. (UFSAR 6.3.3.1.3)

Dominion Resources Services, Inc. Thomas Shaub Technical Consultant Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060 Phone: (804) 273-2763 Fax: (804) 273-3715 E-mail: Tom.Shaub@dom.com (new e-mail address)

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April R. Thorpe, Contract Secretary Plant Licensing Branch 2-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Phone: 301-415-1688 Fax: 301-415-1222 April.Thorpe@nrc.gov E-mail Properties Mail Envelope Properties (1108E05267A25F458B14F9B1D036C5970E59F262)

Subject:

additional clarification for PREACS Sent Date: 7/7/2010 3:35:08 PM Received Date: 7/7/2010 3:35:08 PM From: Tom Shaub

Created By: tom.shaub@dom.com

Recipients:

V.Sreenivas@nrc.gov (Sreenivas, V)

Tracking Status: None

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DOM-MBX05.mbu.ad.dominionnet.com

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