ML20127G433
| ML20127G433 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 05/25/1973 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9211160598 | |
| Download: ML20127G433 (2) | |
Text
r fjDL Te'gutator7 pg g MSP NORTHERN 5TATES POWER COMPANY M I N N E A f* C U S. MIN N E S OTA S S 4 01 b
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May 25, 1973 DOCKETED
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S-x REGULATORY Q}
Mr. J F O' Leary, Director ML SECDON 8
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CKET CLERK oy Directorate of Licensing b
United States Atomic Energy Commission
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Washington, D C 20545 en
Dear Mr. O' Leary:
MONTICELLO NUCLEAR GENERATING PIANT Docket No. 50-263 License No. DPR-22 Inoperability of a Primary Containment Valve T-Ring Seal A condition occurred at the Monticello Nuclear Generating Plant which we are reporting to your office in accordance with Section 6.7.B.1, Abnormal Occurrence Reports, of the Technical Specifications, of the Provisional Operating License DPR-22.
On May 17, 1973, during the performance of an external inspection of the suppression chamber, the T-ring on an air operated reactor building-to-suppression chami.scr vacuum breaker valve (A0 2379) was found depressurized.
This valve is of a butterfly type design with an inflatable resilient seal for positive valve disc seating. When the valve is in the closed position, an actuating arm attached to the valve shaft opens a seal pilot valve allow-l ing air pressure to the seal.
Examination of the valve on May 17, revealed interference between a bolt on the operator linkage and a bolt on the opera-tor support. This interference prevented full valve travel in the close direction and consequently, prevented actuation of the seal pilot valve and inflation of the T-ring seal.
The interference was caused by movement of the actuator arm on the valve
(
shaf t resulting in a misalignment of the valve operator linkage.
The set screw used to position the actuator arm on the valve shaft was found loose.
The valve had been disassembled during the recent refueling outage for inspection and replacement of the T-ring seals; however, the operator linkage was uncoupled above the actuator arm and the entire valve and actuator arm assembly was removed as a unit.
During the process of handling the valve with the loose set screw, the actuator arm moved on the shaft sufficiently to result 3155
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ADOCK 05000263 PDR
2 in the interference between the operator linkage bolt and the operator support bolt. The interference was eliminated by repositioning the actuator arm.
Ad-ditional cicarance between the bolts was provided by reversing the operator support bolt to place the bolt head on the inside of the support plate.
Functional testing of the valve following the rcpairs demonstrated fret opera-tion of the valve to the fully closed position and proper inflation of the T-ring seal.
A subsequent investigation of all dryvell and suppression chamber vent and purge valves of a design similar to that of A0 2379, revealed free operation of these valves with proper inflation of the T-ring seals. The operator actuator arms on these valves were verified to be securely fastened to the valv-shaft. The operator mounting arrangements for these valves are dif-ferent from that of A0 2379 and are not susceptible to the same interference problem.
This occurrence did not affect safe operation since:
1.
Prianary Containment isolation capability was provided by the check valve downstream of A0 2379.
2.
Since A0 2379 was free to operate in the cpen direction, vacuum relief capability between the reactor building and the suppres-sion chamber was noc affected.
One previous T-ring seal inflation malfunction has occurred at Monticello.
As a result v this previous problem, a verification of T-ring pressure on all dryvell.
turus vent and purge valveu vas included in the monthly ex-ternal torus
>ection procedure.
Since the present problem was discovered during the pet emance of tid
'nspection, it is felt that the inspection is ad quately serving its inte 4e function of assuring T-ring pressurization.
Yours very truly, L 0 Mayer, P.E.
Director of Nuc1 car Support Services LOM/br cc: B H Grier G Charnoff Minnesota Pollution Control Agency Attn. Ken Dzugan