ML20084S846

Ro:On 710618,motor Operated Valve MO-3012 on Low Pressure Safety Injection Sys Found W/Broken Yoke & Bent Valve Stem. Investigation Into Cause Incomplete.Valve Yoke Assemblies to Be Replaced

ML20084S846
Person / Time
Site:	Palisades
Issue date:	06/25/1971
From:	Haueter R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084S848	List: ML20084S846
References
NUDOCS 8306200010
Download: ML20084S846 (3)

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' wee u,chegan Avenue. Jachon. Michegan WOI Area Code S17 788-0550 June 25, 1971 Dr. Peter A. Morris, Director Re: Docket 50-255 Director of Beactor Licensing License No DPR-20 United States Atomic Energy Commission Washington, DC 205h5

Dear Dr. Morris:

This letter is written to apprise you of a recent difficulty with the six-inch, motor-operated valves on the Low Pressure Safety In-jection System at the Palisades Plant. At the time the difficulty was detected, the plant was in a cold shutdown condition with the primary system drained down to the center line of the 42 inch nozzles and the internals removed from the four primary coolant pumps for modification.

The auxiliary operator notified the control room at 0640 on June 18, 1971, that the motor-operated valve Mo 3012 on the Low Pressure Safety Injection System had been found with a broken yoke and a bent valve stem. Later examination disclosed that the remaining three sim-ilar valves MO 3008, MO 3010 and MO 3014 had small cracks in the same area in which the failure of MO 3012 had occurred.

Sequence of Events Heatup of the primary system for the post-core-loading hot functional testing was intiated on April 29, 1971. The testing was completed and the system cooled down on May 8,1971 to repair the pri-mary coolant pumps. The safety injection motor-operated valves functioned normally during this cooldown as a part of the shutdown cooling system.

1 All safety injection valves were successfully tested prior to l I

the primary system heatup for the initial approach to criticality on

/ May 22, 1971. Initial criticality was achieved on May 24, 1971.

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' jd '/ .7 The Zero Power Physics Testing was completed on June 4,1971 and

g' Q/ (, the shutdown cooling system placed into service for the primary syetem i

cooldown. The shutdown heat exchanger was bypassed for a short time to l}{

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[) / allow the entire shutdown cooling system to approach 300 F so as to permit a verification of system hanger settings and expansion characteristics at d, j

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Dr. Peter A. Mo'r'is r 2 June 25, 1971 In the maintenance period from June 4,1971 through June 17, 1971, the shutdown cooling system was in continuous operation with numerous operations of the four low-pressure safety injection six-inch motor-operated valves to control the flow of water to the reactor vessel.

At 0640 on June 18, 1971, while making a regular inspection tour, the auxiliary operator noted the damaged yoke on the motor-opera-ted valve 3012 and notified the control room of the problem.

The remaining three similar valves were immediately inspected and noted to each have a small crack in the same area in which the fail-ure had occurred on the yoke of valve MO 3012.

Cause of Incident The investigation into the cause of the failure has not been completed at this time. Early indications are that the yoke is some-what undersize for the motor operator utilized. A small c ack, similar to those noted on the other three valve yokes, had apparently existed for a period of time prior to the failure as this portion of the break surface was discolored with oxidation.

It is postulated that the failure occurred as the va;ve was closing but prior to the time sufficient torque was developed to allow the torque switch in the control circuit to function. As the break occurred, a continued close signal by the valve operator bent the valve stem and the opposite yoke web. The bending action was terminated by the adjacent seismic restraint.

Corrective Action A thorough investigation into the cause of this failure is continuing and will be completed prior to power operation. In addition, the valve yokes on the other safety injection valves have been inspected, with no problems detected.

The valve manufacturer and the vendor have each removed a por-tion of the damaged valve yoke for a fracture analysis and metallurgical analysis.

It is planned to replace all four defective valve yoke assem-blies with new yokes of the proper size, all damaged internals will be replaced with new parts and the repaired valves functionally tested.

The valve yokes will be visually inspected the first year after each monthly test operation to detect early any cracks which could possibly lead to yoke failure.

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7 Dr. Peter A. Mo is D 3 j ,

June 25, 1971 l -

Conclusion The re-evaluation of the valve yor.e design and the adequate replacement of the defective yokes and damaged valve parts will pro-vide reliable valve cperation.

The inspection program will develop an operating history which will indicate the capability of valves to respond at any time they are called upon to function.

Yours very truly, Robert L. Haueter (Signed) t i RLH/pb Robert 7 Haueter Electric Production

CC: BHGrier Superintendent - Nuclear )

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