ML20210U382

Part 21 Rept Re Swing Chiller Control Circuit.Initially Reported on 861003.Circuit Found to Have Deficiency Which Would Prevent Chiller from Starting.Util Informed of Condition & Implemented Appropriate Administrative Controls

ML20210U382
Person / Time
Site:	Summer
Issue date:	10/03/1986
From:	Sailer W GILBERT/COMMONWEALTH, INC. (FORMERLY GILBERT ASSOCIAT
To:	Taylor J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
REF-PT21-86-331-000 PT21-86-331, PT21-86-331-000, NUDOCS 8610090506
Download: ML20210U382 (2)

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[ Gilbert / Commonwealth engineersandconsu:tants GILBERT / COMMONWEALTH, INC., P.O. Box 1498, Reading PA 19603/Tel. 215 T/5-2600/ Cable Gilasoc/ Telex 836431 W.F. SAILER o er 3, N  % 3U Vice President & General Manager Quality Assurance Division United States Nuclear Regulatory Commission Office of Inspection and Enforcement Washington, DC 20555 Attention: Mr. J. M. Taylor RE: Reportable Event Swing Chiller Control Circuit

Dear Mr. Taylor:

This documents a report by telephone under the provisions of 10CFR21 on October 3, 1986, at approximately 3:40 P.M. to Mr. D. P. Allison.

Individual Who Reported Mr. W. F. Saller, Vice President and General Manager, Quality Assurance Division, Gilbert / Commonwealth, Inc. made the call.

Facility involved Virgil C. Summer Nuclear Station, of the South Carolina Electric and Gas Company (SCE&G).

Activity / Component Involved Safety related " swing" chiller in the safety relited Chilled Water System.

Nature of the Defect The plant has three (3) safety related chillers - one for "A" Train, one for "B" train and one " swing" chiller. The " swing" chiller can be connected in place of either the "A" or "B" chiller. The " swing" chiller control circuit was found to have a deficiency which would prevent the chiller from starting, when required, under certain conditions. The scenario for this occurrence is as follows:

The "A" Train chiller has been taken out of service, "B" Chiller l is operating, and the " swing" chiller is aligned to "A" Train. A design basis event (DBE), such as a loss of coolant accident, is postulated simultaneously with the loss of "B" Train de control power as a single failure. The DDE results in a safety injection signal which starts the swing chiller in the "A" loop 8610090506 861003 PDR ADOCK 05000395 g PDR

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GILBCT/CouMONWEALTH, INC, P O Bos 14es. Remhng. PA 19eo3/Tal 215752600/Catse GdasoctTeien 836431 in accordance with the design intent. Should there also be a subsequent loss of offsite power, the design calls for the chiller to be tripped and then restarted in sequence with the on-site diesel generator supplying power. The design also calls for an override of the built in 20 minute time delay for restart of the chiller. However, with the events postulated, it was determined that false signals will be transmitted to the restart permissive control circuitry by the failure of the de control power. These false signals will negate the restart override which will delay the restart of the chiller for up to 20 minutes while the design restart time is 5 minutes. With the chiller restart delayed 20 minutes, the chiller will experience. excessive refrigerant pressure sufficient to burst a rupture disk and release the refrigerant.

Since this sequence of events would have resulted in the simultaneous unavailability of both connected chiller units, it was considered to be a safety hazard. This circuit configuration, originally designed by Gilbert / Commonwealth and subsequently modified by SCE&G, is limited to the Virgil C. Summer Nuclear station.

Date Information Obtained The Reporting Officer, W. F. Sailer, was informed on October 1,1986 of the reportability of this item.

Corrective Action The owner, SCE&G, has been informed of this condition and has implemented appropriate administrative controls until a permanent circuit modification can be made.

The circuit modification is planned for the third refueling outage scheduled for the Spring of 1987.

If you require any further information, please call me at (215)775-2600, Extention 7543.

Very truly yours, W. F. Sailer Vice President & General Manager i

Qaulity Assurnnce Division WFS/BN/pw cc: C. D. Williams W. K. Burkhart R. B. Clary - SCE&G J. M. Taylor (2)

G. G. Zech - Vendor Program Branch, NRC Document Manngement Branch, NRC