ML19309A371
| ML19309A371 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 09/10/1974 |
| From: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML19309A365 | List: |
| References | |
| NUDOCS 8003270824 | |
| Download: ML19309A371 (3) | |
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ABNORMAL OCCURRENCE REPORT T-DOCKET NO. 50-312-74-2
' Reporting Date:
September 10, 1974 Occurrence Date:
September 7, 1974 Time:
10:00 A.M.
Facility:
Rancho Seco Nuclear Generating Station Unit No. T Clay Station, California Identification of Occurrence:
Reactor Building Emergency Sump Isolation Valve HV26106 would not open.
Condition Prior to Occurrence:
The plant was at refueling shutdown completing final testing prior to initial criticality.
Description of Occurrence:
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The long term recirculation system following a loss of coolant accident is provided by the low pressure injection system. The system is redundant except for a common sump in the Reactor Building'. Two independent 18 inch diameter lines originate at the sump and penetrate the Reactor Building.
Each line has an enclosed isolation valve outside the containment that serves four purposes:
1.
They isolate the sump from the decay heat pump suction during low pressure injection to prevent the borated water backflowing into the sump.
2.
They isolate the sump from the decay heat pump suction during cooldown when suction is taken from the Reactor Coolant System.
3.
They provide water to the low pressure injection system for long-term cooling when the Borated Water Storage Tank empties.
4.
They provide Reactor Building isolation if the line downstream of the valve fails.
These valves normally remain closed for all operations except as explained in 3 above.
Surveillance testing requires that these valves be cycled once a quarter. On September 7, 1974 both Isolation Valves were tested. Motor operated HV26105 opened and shut as required. The motor operated ilV26106 failed to open electrically. An attempt was then made to' open it manually and this also failed. In observing its operation it was found that the stem traveled approximately 1/4" before stopping.
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Corrective Action'Taken:
The motor operator was removed a.d inspected for any damage.
Also the torque switch settings were reverified te insure that the valve was not.
being over-torqued in the shut direction nor rec,1ving insufficient torque for' the opening direction.
The torque switch settings were verified.co be proper.
.The motor operator itself appeared to be in excellent condition and was not the cause of the valve failure. The valve was then disassembled and it was found that-the valve wedge-type gate was actually. stuck in the seac. After initially jacking the gate partially open, it was found that the. stem and gate would move easily to the fully open position.
Both the gate and seat were carefully inspected and-there was no indication of damage, binding or galling. The valve was reassembled with proper torque limit switch setting and tested.
It subsequently performed both open and shut operations satisfactorily., This final leak' rate testing was completed on September 12, 1974.
Designation of Apparent Cause: Other.
There was no apparent reason why the valve stuck.
Analysis of Occurrence:
. Records indicated that the valve had not been operated since December 5, 1973, when a local leak rate test was-performed.
The valve had been in a closed position for approxicately nine months without being exercised.
During this time a bond may have developed between the seat and gate seal surfaces.
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However, there was no evidence of this-during the inspection of the valve.
The valve is normally dry on the Reactor Building side of the disc but can be wetted -
from the Decay Heat removal side.
Equipment I.D.:
The plant designation for this valve is HV26106. The valve is manufactured by Darling Corporation and is a Class I, 18-inch stainless steel valve rated for 300 psig and 300*F.
It is an A461 type 630 valve for an H1150 condition.
The packing is 10 rings of asbestos 1871 manufactured by J. Crane Company.
The valve operator is a Limitorque-type SMD-0-40.
Action Required to Prevent a Reoccurrence:
A modified test program will be instituted on this valve during e
l the forthcoming months-to determine if a malfunction is occurring due to the valve:
being in the shut position for a lengthy period of time.
The program will be to:
(1) Operate the valve after it has been shut'for two weeks; (2) Allow the valve to set'in the shut position for one month and retest; (3) Allow the valve to set in the shut position for a two month period and cetest.
If the valve functions properly during this testing it.will'then be returned to a quarterly surveillance test program.
In the' event that this modified test program'shows that the valve
-will stick if not operated more frequently than once.a ~ quarter, the surveillance program for exercising the valve will b'e modified accordingly.
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i Failure Data:
l There have been no previous failures of this valve.
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