ML20090A768

Provides Addl Info to Clarify Response to 10CFR50.63, Loss of All Alternating Current

ML20090A768
Person / Time
Site:	Limerick
Issue date:	02/14/1992
From:	PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9203030091
Download: ML20090A768 (2)

Text

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PillLADELPillA ELECTRIC COMPANY NUCLEAR GROUP llEADQUARTERS 955-65 CilESTERBROOK BLVD.

WAYNE, PA 19087 5691 (215) 640 600C NUCLEAR LNGtNEERINO & SERVICES DEPARTMENT February 14, 1992 i

Docket Nos. 50-352 50-353 License Nos. NPF-39 NPF-85 -

U.S. Nuclear Regulatory Commisslori Attn: Document Control Desk Washington, DC 20555

SUBJECT:

Limerick Generating Station, Units 1 and 2 10CFR50.63, " Loss of All Alternating Current" \

Response to NRC Concerns i

This letter provides additional clarifying information as discussed during a telephone conversation between representatives of the NRC and Philadelphia Electric Company (PECo) on February 3, 1992.

This telephone conversation was in regard to the NRC's review of additional information previously provided by PECo in a letter dated September 4, 1991 as requested by the NRC by letter dated June 3, 1991 which forwarded the NRC's Safety Evaluation (SE) and supporting Technical Evaluation Report (TER) concerning PECo's responses to 10CFR50.63, "Locs of All Alternating Curre;t," for Limerick Generating Station (LGS), Units 1 and 2. During the telephone conversation, the NRC identified concerns with respect to the Main Control Room (MCR) maximum initial temperature, opening of equipment cabinet doore within 30 minutes frca the onset of a Station Blackout (SBO), the revised Reactor Core Isolation Cooling (RCIC) room maximum temperature, and the inputs and assump' ions for the revised SBO calculations described in the September 4, 1991 submittal.

With respect tn the initial MCR temperature used in the heat-up calculations, the 5RC expressed a concern that PECo should establish administrative procedures to ensure that during normal operation, the MCR temperature will not exceed the initial room temperature used in the heat-up calculation. Such procedures already exist. The heat-up 2

calculation assumes an initial temperature of 83 F. The plant daily

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9203030091 920214 "

gDR ADOCK 05000352 enR 1 D'

• • "b LGS Units 1& 2, 10CFR50.63 February 14, 1992

" Loss of All Alternating Current" Page 2 I Response to NRC Concerns surveillance log, Surveillance Test (ST) Procedure ST-6-107-590(1)-0-1-2, requires . hat the average MCR temperature be 70 F or less. If that temperature is exceeded, Off-Normal (ON)

Procedure ON-ll5, " Loss of Control Enclosure Cooling," is entered.

This procedure provides direction to reduce temperature in the MCR and Auxiliary Equipment Room (AER) to below 78 F. These existing procedures are sufficient to provide reasonable assurance that the C3 F initial MCR temperature assumed in the heat-up calculation is ,

conservative.

With respect to the peak calculated temperatures for the MCR, RCIC room, and AER, the NRC expressed a concern that cabinet doors in these rooms should be opened within 30 minutes from the onset of an SBO. It is PECo's position that this time is better spent in re-acquiring room ventilation. In SBO event in Unit 2 will not af'ect MCR ventilation since the common MCR ventilation system is supplied power from Unit 1. Therefore, opening cabinet doors for this event is not necessary. An SBO event in Unit I will cause loss of the common MCR ventilation system. However, the use of an existing procedure to cross-tie the Unit 1 buses to the excess Unit 2 diesel generation capacity, which is achievable within 30 minutes, will ensure that ventilation for these areas is reestablished. Therefore, opening the cabinet doors is again unnecessary. The calculated maximum temperatures for these rooms during an SBO, together with the expected room-to-cabinet temperature differentials of less than 10 F allow us to conclude that a blanket procedure to open cabinet doors within 30 minutes of an SBO is unnecessary.

As identified by the NRC, our September 4, 1991 submittal did not provide the revised calculated peak temperature for the RCIC room.

This temperature was inadvertently omitted. The peak RCIC room temperature, occurring 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after the onset of the SBO event is 142 F. ,

As discussed during the telephone conversation, the revised heat-up calculations for the MCR, RCIC room, and AER were performed in an effort to justJfy a minimization of required operator actions follouing an SBO event. These calculations utilize methode, inputs, and assumptions that are all appropriate for their intended purpose.

These calculations are maintained by PECo in our SBO files, and are available for NRC review.

If you have any further questions or require additional information, please do not hesitate to contact us.

b Manager Licensing Section Attachments cc: T. T. Martin, Administrator, Region I, USNRC w/ attachments T. J. Kenny, USNRC Senior Resident Inspector, LGS w/attachmonts c .. d .

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