ML13333A456

Responds to NRC Re Operation of Containment Purge & Vent Valves Pending Resolution of Isolation Valve Operability.Purge Valves Closed During Reactor Operation Until Operability Under Design Basis LOCA Is Proven

ML13333A456
Person / Time
Site:	San Onofre
Issue date:	12/14/1979
From:	Baskin K Southern California Edison Co
To:	Ziemann D Office of Nuclear Reactor Regulation
References
TASK-06-04, TASK-6-4, TASK-RR NUDOCS 7912210369
Download: ML13333A456 (2)

Text

Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 K. P. BASKIN December 14, 1979 TELEPHONE

MANAGER, GENERATION ENGINEERING 213-572-1401 Director of Nuclear Reactor Regulation Attention:

D. L. Ziemann, Chief Operating Reactors Branch #2 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Gentlemen:

Subject:

Docket No. 50-206 Containment Purging and Venting San Onofre Nuclear Generating Station Unit 1 Your letter of October 23, 1979 requested that we make certain interim commitments regarding the operation of the containment purge and vent valves at San Onofre Unit 1 until qualification of the valves is completed. The commitments were outlined in an enclosure entitled, "Interim Position for Containment Purge and Vent Valve Operation Pending Resolution of Isolation Valve Operability."

As requested by the enclosure to your letter, the purge valves at San Onofre Unit 1 will be maintained closed whenever the reactor is not in a cold shutdown or refueling mode. This condition will be maintained until it can be demonstrated that the purge valves will be operable under the design basis LOCA flow conditions. The valves at San Onofre Unit 1 are Henry Pratt 24" butterfly valves.

We are presently pursuing a qualification program with the valve vendor. The vendor has indicated that completion of a qualifica tion program for the San Onofre Unit 1 valves would be about July, 1980.

The vent system at San Onofre Unit 1 consists of a 6" equalizing line which penetrates containment with two 6" butterfly valves (CV 116 inside containment and CV 10 outside containment).

There is also a 2" line inside containment which vents the instrument air exhaust to the 6" equalizing line. There is a normally open 2" containment isolation valve located on this instrument exhaust line.

The 6" butterfly valves are normally open during reactor operation.

The purpose for keeping the valves open is to maintain the containment holyI

-2 at or below atmospheric pressure. This is necessary to satisfy the conditions of the containment pressure-temperature analysis. We are pursuing with the valve vendor, Fisher Controls, the capability of the valve to close from the fully open position with the San Onofre Unit 1 design basis LOCA flow conditions. Based on discussions with the vendor, they anticipate no problem in demonstrating the ability of the 6" valves to close; however, the analysis to confirm this position is not yet complete. The vendor's position is based upon preliminary calculations and the successful testing of a similar type 6" butterfly valve to close against above normal pressures. Further details of this testing have not been made available to Southern California Edison Company by the vendor since it is considered proprietary data. Results of the vendor's analysis should be available within 2 weeks and we will inform you of these results at that time.

Pending completion of that analysis, it is our intention to continue to maintain the 6" butterfly valves normally open during reactor operations.

The purge valves and the vent valves will automatically close upon receipt of an isolation signal from any one of the following:

(1) high containment pressure, (2) high containment radiation, or (3) safety injection actuation. As indicated in the discussion of our January 9, 1979 letter, only the safety injection actuation signal can be manually overridden. During reactor operation the manual override is only utilized during plant cooldown to prevent inadvertent automatic actuation of the safety injection system. In the event containment isolation is required when the safety injection signal is overridden, isolation will be accomplished upon receipt of a high containment pressure or high containment radiation signal. Therefore, the purge and vent valves would still close if the safety injection signal were not present.

Consequently, modification of the containment isolation signals to the purge and vent valves is not necessary at San Onofre Unit 1.

If you have any questions regarding this matter, please let me know.

Very truly yours,