ML19256G531

Forwards LER 79-037/03L-0

ML19256G531
Person / Time
Site:	Cooper
Issue date:	12/12/1979
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19256G532	List: ML19256G531 ML19256G533
References
CNSS790636, NUDOCS 7912310438
Download: ML19256G531 (2)

Text

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COOPER NUCLEAR STATION P.o. BOX 98, BRoWNVILLE, NEBR ASKA 6832i Nebraska Publ.ic Power Distr.ic t TELEP-o~E c402i 2s.3.ii

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CNSS790636 December 12, 1979 n.-, .

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Mr. K. V. Seyfrit U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region IV 611 Ryan Plaza Suite 1000 Arlington, Texas 76011

Dear Sir:

This report is submitted in accordance with Section 6.7.2.B.2 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occurrence that was discovered on November 13, 1979. A licensee event report form is also enclosed.

Report No.: 50-298-79-37 Report Date: December 12, 1979 Occurrence Date: November 13, 1979 Facility: Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which resulted in operation in a degraded mode per-mitted by a limiting condition for operation established in Section 3.5.F.2 of the Technical Specifications.

Conditions Prior to Occurrence:

The reactor was at 82% of rated thermal power. No. 2 diesel gen-erator was inoperable. Reference LER 79-36.

Description of Occurrence:

While performing surveillance procedure 6.3.12.1, to prove oper-ability of No. I diesel generator as required by Technical Spec-ification 3.5. F.1, No. 1 diesel generator failed to start auto-marica11y.

Designation of Apparent Cause of Occurrence:

The failure of No. 1 diesel generator to start was due to the silencer bypass solenoid valve disc stopping in the mid pcsition venting the control air header. This prevented the control air header from reaching sufficient pressure to open the fuel racks 3/

supplying fuel to the engine. ff h, \

1657 161 3912310f3& 2

v Mr. K. V. Seyfrit December 12, 1979 Page 2. -

Analysis of Occurrence:

The silencer bypass solenoid valve is an ASCO Model 8344A72 four way solenoid valve, The valve is a two position four way valve.

Air pressure is ported by the solenoid valve to position the main valve disc. Its function is to open the silencer bypass valve at a pressure in the exhaust system of 1.0 psig, which would indicate a restriction in the silencer or exhaust stack. The solenoid valve disc requires approximately 1085 scfh of air to shift positions.

If sufficient air supply is not present the disc will stop in the mid position where it vents all ports. In the application on the diesel generator, the valve is at the end of a 80 psi control air line. On a diesel generator start, the air pressure in the line builds up slowly to 80 psi while operating the engina intake shut-down valves and the fuel racks. If the disc is in the deenergized position at the time the air pressure starts to build up, there is insufficient air capacity to operate the pneumatic valves, fuel racks and position the solenoid valve disc. This causes the solenoid valve disc to stop in the mid position where it vents the control air system, preventing the diesel from starting.

Since the normal, startup and emergency transformers were available and this diesel generator could have been manually started, this event presented no major consequences which were adverse to public health and safety.

Corrective Action:

A reduction in power was immediately commenced as required by Technical Specification 3.5.F.2. The silencer bypass solenoid was replaced with an identical replacement and the dicsel generator was started three times to verify operability. Further investigation to insure that the cause of the failure had been corrected revealed the misapplication of the solenoid valve. To insure operability of both diesel generators while the design of the system is reviewed, the silencer bypass valves were opened and the air supplies to the silencer bypass solenoids were capped. The system design will be evaluated by the vendor to determine the most reliable means of operation.

Sincerely,

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// 4+m L. C. Lessor Station Superintendent Cooper Nuclear Station 3

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