ML20128D974
| ML20128D974 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 03/13/1974 |
| From: | Fiorelli G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Thornburg H US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20128D972 | List: |
| References | |
| NUDOCS 9212070436 | |
| Download: ML20128D974 (1) | |
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- 11. D. ThornburC, Chief Field Support and Enforcement Branch, Regulatory Operations, !!cadquartero UORTif ER11 STi.TES l'0UER C0!!PANY (110STICELLO)
DOCi'ET NO. 50-263 FAILURE OF MS1V PILOT VALVES The attached 1Jcensee report involving the cause of the failure of two MSIV's is f eruarded for your information and possible action. The 11 cent.ee relates the cause to a generic design problem.
The specific component which failed in the CE recor= ended replaccrent component for the MS1V pilot spool valves unnufactured by Numatien. On thic basis ec recot=end issuance of an R0 Bulletin inforcint, licenseen of t.he potential problem.
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Xaeton' Flore111, Chief Reactor Operations Branch
Attachment:
Licensee Report cc B. H. Grier, RO HQ J. G. F.eppler, RO III
- 11. C. Dance, RO III l
l 9212070436 740404 i
PDR ADOCK 05000263 G
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.f NOHTHERN STATCC POWEH C0MPANY 1
M I N N F A P O L. l p. M I N N et e O T A 5 5 4 01
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7, February 25, 1974 3
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70 t!r. J F O' Leary E'
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U S Atomic Energy Cenraission (3.,,,,
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Dear !!r. O' Leary:
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l lio::TICELLO NUCLEAR GE'iERATI! G PLA!iT Docket 1:o. 50-263 Licence No. DPR-22 Failure of Outboard itain Steam isolation Valves A0-2 86B and A0-2-86C to Close A condition occurred at the 1!onticello 1:uc1 car Cencrating plant which we are reportin;; to your office in accordance with Section 6.7.g.1, Abnormal Occurrence Reportc. of Appendix A. Technical Specificat/' 1 of Provisional Operating License DPR-22.
4 On February 16, 1974, while performing a routine surveillance test, two outboard 11SIV's, A0-2-86B and A0-2-86C failed to close using the control room handsvitch.
The redundant 11SIV's on the "B" and "C" steam lines were closed and the reactor was brought to a hot standby condition while an invectigation was conducted.
It was found that the AC solenoids on the ?!31V air operators vore not venting properly when dcenergized.
The solenoid manifolds for A0-2-86B and A0-2-86C vere disassembled and inspected.
The chips were the result of inadequate deburring end cicaning of the manifold during manufacture.
Further investigation revealed a generic design problem with the solenoid valves.
It had been noted that the AC solenoids on the outboard 11SIV's exhibited leakage through their exhaust ports.
It was found that the viton seats in the solenoid plungers had assumed a permanent defor.r.ation.
It uns postulated that 1cakage through the exhaust port could create a low proccure area across the top of the plunger, resulting in a differential pressure force sufficient to prevent plunger operation.
The plausibility of this theory uns confirmed by calculations and demonstrated by bench tests of a solenoid manifold.
'Ihese tests demonstrated that solenoid valves with exhaust port Icahage would fail to operate upon dcenergization when operating at pressure near the normal supply pressure of 100 psig.
1on-1 caking valves operate proper!y at pressures beyond 150 psig.
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lir.'J F O' Leary rebruary ?.$, 1974
.Paqc 2 The solenoids and manifolds for all main steam isolation valves were disasser. bled and cicaned.
- cv plungers with spring cuchioned upper seats were installed in all !!SIV AC solenoids.
The spring cushioned seats will:
- 1) Limit seating force, thereby reducing deformation and promoting longer seat life.
'2) Remain scated durina, the initial motion of the plunger, thereby minimizing flow in. 'ed forces.
3) provide cdditional spring force to assist the initiation of plunger movement.
All !!SIV's were demonstrated to function properly prior to returing to pouer operation.
The calfunction of two of the four outboard 11SIV's would not have provented an automatic isolation of the enin steam lines, since the inboard MSIV's were all fully operable, llouever, the ralfunction was of a generic nature.
It-is noted that the MS1Y's in the stcom chase are exposcd to a higher ambient temperature than there in the dryvell.
This temperature difference (approx.1500r vs.110 f) 0 may have contributed to the cdditional seat leahnge observed on the outboard MSIV's.
The precent MSIV solenoid valves vere manufactured by the Allied Control Company, Inc., of plantsville, Connecticut for the Automatic Valvo Corporation, of Fannington, Michigan and were installed during the spring,1973 refueling outage.
Execp t for a MSIV cxcrcise test overtravel during the first routine HSIV cxercise closure following installation, this is the first failure of this type of solenoid valvo.
This type of solenoid valve is not used on any other safety related system.
The design of the solenoid valves on other systems is not susceptible to this type of failure.
Although the modified plungers reduce the potential for a recurrence, ue are continuing to investirate the possibility of further modifications.
The solenoids and manifolds will be inspected during the spring, 1974, refueling outage.
Yours very truly,
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p L 0 !!ayer, pE Director of 11ucicar Suppor t Services LObt/kn ec:
J C Keppler G Charnoff Minnesota-pollution Control Agency.
Attn. E A pryzina 4
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