ML19320C337

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Responds to NRC Request for Addl Info Re Residual Heat Removal Sys.Addresses Use of Pressurizer power-operated Relief Valve for Pressure Reduction of RCS & Advises of Blown Rupture Discs.Precaution Will Be Added
ML19320C337
Person / Time
Site: North Anna Dominion icon.png
Issue date: 07/14/1980
From: Sylvia R
VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To: Harold Denton, Youngblood R
Office of Nuclear Reactor Regulation
References
620, NUDOCS 8007160671
Download: ML19320C337 (2)


Text

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O VIRGINIA ELECTRIC AND Powen COMPANY Rrenwown,VzmoxxzA 20261 l July 14, 1980 l

Mr. Harold R. Denton, Director Serial Number 620 Office of Nuclear Reactt,r Regulation N0/ERSjr/sjl Attention: Mr. B. Joe Youngblood, Chief Docket No. 50-339 Licensing Branch No.1 License No. NPF-7 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20555

Dear Mr. Denton:

RESIDUAL HEAT REMOVAL (RHR)

ADDITIONAL INFORMATION NORTH ANNA POWER STATION UNIT NO. 2 Members of your staff have requested additional information concerning the Residual Heat Removal (RHR) system for North Anna Unit No. 2.

In previous correspondence, we have addressed the use of auxiliary pressur-iter spray ' " ~4ing the use of a portable supply of motive power. Auxiliary spray is _ by an air operated valve and connects to the charging line of the eical and Volume Control System. The motive force for this system is charging pumps powered by the emergency busses.

We have further determined that the pressurizer power-operated relief valve (PORV) could be used for pressure reduction of the reactor coolant system, if required. The PORV discharges to the pressurizer relief tank (PRT). The PRT contains rupture discs and this tank is designed for a range of pressure from full vacuum to 100 psig. The tank is equipped with the following instrumentation (and alarms):

Level High alarm at 78%

Pressure High alarm at 8 psig Temperature High alarm at 112*F We have in the past experienced failed (blown) rupture discs. These events have not caused (from our observations) extreme containment environments, except for higher than normal airborne activity. Personnel have entered containment for detailed walkdowns after such events. They were not sub-jected to extreme conditions; however, they were required to wear self-contained breathing apparatus to protect against possible airborne contaminants.

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Vasorw4 Etzernic Aun Powen COMPANY TO Mr. Harold R. Denton 2 Use of the PORV as an alternate method of pressure reduction is a controlled process. The PORV is opened manually frca the control room. It discharges underwater in the PRT. An operator performing this task can monitor the process and stop the discharge when required. He would then drain and/or vent as required to return the PRT to a normal status. He may refill, if necessary, with primary grade water. This is not a complicated process and can be accomplished with full confidence. The facility coul.d be cooled down and depressurized in a controlled, step-wise fashion; i.e.,

first, reducing temperature; then reducing pressure. The PRT rupture discs would not be expected to fail because of use of the PORV's.

We fully believe that reactor coolant system cooldown and depressuri-zation can be accomplished by alternate methods. In order to improve guidance to operators when using the PORV for pressure reduction, we will add a precaution to appropriate procedures to warn of potential failure of the PRT rupture disc.

This information should permit you to conclude your review of this item.

Should you have any further questions, please contact us.

Very truly yours,

(

B. R. Sylvia Maaager Nu'elear Operations & Maintenance cc: Mr. James P. O'Reilly