ML19262A183

Abnormal Occurrence 50-289/74-33:on 741230,1A Decay Heat Pump Suction Valve from Borated Water Storage Tank Inoperable.Caused by Circuit Breaker to Motor Operator Having Tripped Open on Overcurrent Condition.Breaker Reset

ML19262A183
Person / Time
Site:	Three Mile Island
Issue date:	01/10/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
NUDOCS 7910260510
Download: ML19262A183 (4)

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A0-50-289/74-33 on 12-30-74 re inability to -

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Dear Sir:

Docket No . 50-289 Operating License No. DPR-50 In accordance with the Technical Specifications for our Three Mile Island Nuclear Station Unit 1, we are reporting the following abnormal occurrence:

(1) Report Number: A0 50-289/74-33 (2a) Report Date: JAN 101975 (2b) Occurrence Date: December 30, 1974 (3) Facility: Three Mile Island Nuclear Station Unit 1 (TMI-1)

(4) Identification of Occurrence:

Title : Inability to operate the 1A Decay Heat Pump Suction Valve from the Borated Water Storate Tank.

Type: An abnormal occurrence as defined by the Technical Specific-ations, paragraph 1.8d, in that the Inability to operate the 1A Decay Heat Pump Suction Valve from the Borated Water Storage Tank threatened to cause an Engineered Safety feature or system to be incapable of performing its intended function.

(5) Conditions Prior to Occurrence The reactor was at steady state power with major plant parameters as follows:

Power: Core : 100%

Elec.: 865 MW (Gross)

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RC Flow: 139 x 10 lb/hr RC Pressure : 2150 psig RC Temp.: 579 F PRZR Level: 240 in.

PRZR Temp.: 650 F (6) uascription of Occurrence While performing a pretest valve line up, in preparation for a High and Low Pressure Injection Logic Channel and Component Surveillance Test, the Decay Heat Pump Suction Valve (DH-V5A) from the Borated Water Storage Tank (BWST) failed to close. The failure occurred when actuating the valve using its remote pushbutton in the control room.

The redundant Decay Heat System Suction Valve from the BWST was then tested and verified to be operable; and investigations into the in-operability of valve DH-VSA revealed that the motor circuit breaker for the valve had tripped. The breaker was then reset, the valve s

successfully opened and closed using the remote pushbutton operator in the control room, and the subject test completed satisfactorily.

(7) Apparent Cause of Occurrence The valve was inoperable due to the circuit breaker to the motor operator having tripped open on an over-current condition. It has been determined that the over-current condition resulted from a broken, chattering auxiliary contact in the opening t' tor-starter (which works in conjunction with both the opening and closing motor starters) in that the contact caused a rapid cycling of closing current to the motor. There fore , the apparent cause of the occurrence was component failure.

It should also be noted that our telegram report of this occurrence dated December 31, 1974, referenced possible valve stem binding as a potential cause of the occurrence (this could have caused a cycling of the valve torque limit switch, which in turn could have caused a cycling of current to the motor and resultant over-load condition).

As a result of further investigations , however, this is not believed to have been the cause of the occurrence.

(8) Analysis of Occurrence It has been determined that the inability to operate Decay Heat Suction Valve DH-VSA from the BWST did not represent a threat to the health and safety of the public in that only one of the two existing subject borated water flow paths is required to be available for emergency use, and the "B" flow path was verified to be available.

(9) Corrective Action Corrective action was taken as described above to ensure operability

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- of the redundant flow path. In addition phasa resistance and insulation resistance measurements were taken to verify that no electrical faults were present in the cable or motor; and upon discovery of the broken auxiliary contact , the contact was re-placed. Also, as reported in our telegram dated December 31, 1974, the valve stem was lubricated, and the valve packing tight-ness checked, to guard against the potential problem of the valve s tem binding.

The Plant Operation's Review Committee (PORC) met shortly after the occurrence, and at that time the actual cause of the occurrence was not known for sure. Therefore , PORC approved all actions described thus far, except for those relating to the defective auxiliary con-tact, and in addition recommended additional corrective actions to try to determine the exact cause of the occurrence.

The Station Superintendent concurred with PORC 's findings , the cause of the occurrence has been determined and corrected, and PORC will review and, if appropriate make additional recommendations for the Station Superintendent 's consideration.

(10) Failure Data

a. Previous Failures: None

b. Equipment Identification: ITE Model A20CCC Motor Starter Size 1 Sincerely, n -

k(,b')%M R. C . Enold Vice President RCA:RSB:tas File: 20.1.1 7.7.3.5.1 cc: Mr. J. P. O 'Reilly (DORO-Region 1) 1482[l72