ML20117C745

Special Rept 85-02:on 850225,electromatic Relief Valves NR-108B,NR-108C & NR-108D Failed to Fully Reseat After Initial Actuation,Per Tech Spec 6.9.3.f.Caused by Valve Design Deficiency.Design Change Considered

ML20117C745
Person / Time
Site:	Oyster Creek
Issue date:	04/25/1985
From:	Fiedler P GENERAL PUBLIC UTILITIES CORP.
To:	Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
85-02, 85-2, NUDOCS 8505090518
Download: ML20117C745 (3)

Text

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GPU Nuclear Corporation NggIgf Post Office Box 388 Route 9 South Forked River.New Jersey 08731-0388 609 971-4000 Writer's Direct Dial Number:

April 25, 1985 Dr. Thomas E. Murley, Administrator Region I U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406

Subject:

Oyster Creek Nuclear Generating Station Docket No. 50-219 Special Report 85-02 Enclosed is Special Report No. 85-02 which is submitted in accordance with Technical Specifications 6.9.3.f.

If any questions or comments should arise, please contact Mr. Drew Holland, Oyster Creek Licensing Manager at (609)971-4643.

Very truly yours, n il _'Q Peter iedler Vice President and Director Oyster Creek PBF/DGH/ dam Enclosure cc: NRC Resident Inspector Oyster Creek Nuclear Generating Station Forked River, NJ 08731 8505090518 850425 PDR ADOCK 05000219 S PDR GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation l

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0YSTER CREEK NUCLEAR GENERATING STATION Forked River, New Jersey 08731 Special Report 85-02 Report Date April 25,1985 Occurrence Date February 25, 1985 Identification of Occurrence r During the operability tests Electromatic Relief Valves (EMRVs) NR-1088, NR-108C and NR-1080 failed to fully reseat after their initial actuation. The valves reseated after repeated actuations.

This event is reportable in accordance with Technical Specifications 6.9.3.f.

Conditions Prior to Occurrence Power 19.3 MWT 0 MWE The plant was in the start-up mode.

Description of Occurrence On February 25, 1985, during the performance of procedure 602.4.003 -

"Electromatic Relief Valve Operability Test", EMRVs NR-1088, NR-108C, and NR-108D failed to reseat completely after their initial actuation. The valves reseated as follows: NR-1088 after two actuations; NR-108C after eight actuations; and NR-1080 after three actuations. Yalves "B" and "C" leaked initially before reseating. Valve "D" remained open until the third '

actuation. These conclusions were determined by monitoring the acoustic monitors. ,

Apparent Cause of Occurrence The difficulty in attaining a complete shutoff after actuation is apparently due.to the design of the valve. In order to regain a leak-tight shutoff the valve disc is required to reseat in the same position from which it lifted.

The narrow seating area and the existing clearance make this extremely difficult.

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Special R;p:rt 85-02

[ Pags 2 Analysis of Occurrence and Safety Assessment The function of the EMRVs is to depressurize the reactor to allow the Core Spray System to operate during a small break loss of coolant accident. In addition, the valves actuate on high reactor pressure transients to maintain reactor pressure below the safety valve setpoint.

The failure of NR-1088 and NR-108C to fully seat is considered of minimal safety significance since leakage through the seat was well within the makeup capability of the Control Rod Drive System.

EMRY NR-1080 apparently stuck partially or fully open until actuated three times. The safety significance of this failure is of more concern. If a relief valve were to remain open while at power and a loss of feedwater occurred, the results would be similar to a small break LOCA. However, because the steam would be discharged directly to the suppression pool, no increase in drywell pressure would occur and the logic for automatic depressurization would not actuate, operator action would be required to mitigate the consequences of this event to adequately control reactor level.

Alarms and instrumenation are provided to alert the operator of this event.

Because of the potentially higher probability of failure of untested valves following maintenance, the testing of EMRYs is intentionally scheduled during startup, prior to reaching significant power levels. Under these conditions of very low power and very low decay heat, the safety significance of the failure of NR-1080 to close is minimal.

Corrective Action Yalves "C" and "D" were disassembled, inspected and rebuilt. Other than the seat area and clearances, no cause was found for the problem. The valves were tested, reinstalled, and operated successfully.

For future improvements, the manufacturer of the valves is being contacted :.o investigate changing the seat configuration. In addition, the maintenance procedure will be revised to reflect any improvements.

(0666A)