ML19317F123

AO-287/74-03:on 740915,Failure to Maintian Containment Integrity Occurred During Repairs to Engineered Safeguards Valve 3CS-5.Caused by Incorrect Evaluation Re Intermittent Operability of Valve

ML19317F123
Person / Time
Site:	Oconee
Issue date:	09/27/1974
From:	DUKE POWER CO.
To:
Shared Package
ML19317F119	List: ML19317F118 ML19317F123
References
NUDOCS 8001080818
Download: ML19317F123 (2)

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DUKE POWER COMPANY OCONEE UNIT 3

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Report No.: A0-287/74-3 Report Date: September 27, 1974 Occurrence Date: September 15, 1974 Facility: Oconee Unit 3, Seneca, South Carolina Identification of Occurrence: Failure to maintain containment integrity during repairs to Engineered Eafeguards valve 3CS-5 i

Conditions Prior to Occurrence: Power operation at approximately 14 percent full power Description of Occurrence:

On September 11,-1974, the valve 3CS-5 appeared to be intermittently inoperable.

Engineered Sefeguards Reactor Building isolation valve 3CS-5 in the quench tank drain line, located in the Reactor Building. Preliminary investigation by operations and maintenance personnel indicated a malfunction of the control switch in the control room. On September 11, 1974, a work request was initiated to have 3CS-5 checked, and the work was scheduled for September 14 during a scheduled maintenance outage. Between September 11 and 14, power escalation testing continued at 14 percent power, then the unit was brought to a hot shutdown condition at 531 F and 900 psi. The second Engineered Safeguards Reactor Building isolation valve in the quench tank drain line, 3CS-6, was tagged closed prior to commencement of maintenance activities on 3CS-5.

On September 14, the valve was disassembled, checked, and reassembled.

Electricians checking the motor operator found that the valve had been jammed in the open. position, and the operator motor burned. ,

The burned motor was replaced, but on the morning of September 15, it was found that the replacement =ctor was drawing excessive current, and additional adjustments had to be made on the motor operator.

-At approximately 0800 on September 15, 1974, it was realized that the require-ments for; containment integrity were not met. Section 1.7d of the Oconee Technical Specifications requires;that all automatic containment isolation valves be operable or locked closed for containment integrity to exist. The valve 3CS-5 was manually' closed, and pressure and temperature were reduced to 1900 F and 410 psi.

Designation of Apparent Cause of Occurrence: 4

-The apparent cause of this occurrence was the incorrect evaluation of the cause for the intermittent operability of valve 3CS-5. Early investigation-8001080 [/ [ '

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n of the problem indicated the problem was caused by a faulty switch in the control room. This control circuit is in parallel with the Engineered Safeguards actuation circuitry. The first indication that the valve itself was inoperabic was found during actual maintenance on the valve on September 14.

Contributing to the cause of the occurrence was failure by operations personnel to' realize that all conditions required for maintenance on the containment isolation valve had not been met.

Analysis of Occurrence:

If Engineered Safeguards actuation had occurred during the interval of this occurrence, containment integrity would have been maintained. The redundant valve in the quench tank drain line, 3CS-6, was fully operable during uni; opesation and was locked closed during maintenance on 3CS-5. Therefore, it is concluded that this incident did not affect the health and safety of the public.

Corrective Action:

Immediate corrective action upon discovery of the occurrence was to reduce reactor coolant system te=perature and pressure to 190 F and 410 psi. To prevent recurrence, the events of this incident and the appropriate action that should have been taken have been reviewed with all operations personnel.

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