ML19263D352

LER 79-020/01T-0 on 781107:during Controlled Steam Lift, Discovered Warn Ring Lockpin Had Broken on Four Occasions. Caused by Lockpin Fragility.Lockpins Replaced W/Ones of Stronger Design

ML19263D352
Person / Time
Site:	Arkansas Nuclear
Issue date:	03/22/1979
From:	Shively C ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19263D333	List: ML19263D332 ML19263D338 ML19263D343 ML19263D346 ML19263D352
References
LER-79-020-01T, LER-79-20-1T, NUDOCS 7903270485
Download: ML19263D352 (5)

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ol' s!.3"J60LL_)@l0 i s oCOCL 101013 l 6 18l@:1 l1 lEVENT 0 l DATE 7 8 61 E T %MBER -4 63 74 75 CATE 80 EVFNT DESCRIPTION AND PROBAOLE CONSEQUENCES h o 2 i During testing of the Main Steam line code safety valves, executing a i o 2 l coatrolled steam lift, it was disecvered that the varn ring lockpin had I o Ai ibroken on four separate occasions. 2PSV1002 lockpin broke on 11/7/78 and; n s l11/20/78. 2PSV1052 lockpin broke twice on 11/21/78. The relieving  ;

O g, Icapacity of the remaining safety valves exceeded that required for safe ,

a i l operation, as dictated by T.S. Table 3 7.1. ReportableperT.S.6.91.3.({}.

o e 1 No similar occurrences.  ;

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1. Reportable Occurrence Report No. 50-368/79-020

2. Report Date: 03/22/79 3. Occurrence Date: 11/7/78 4 Facility: Arkansas Nuclear One - Unit Two Russellville, Arkansas 72801

5. Identification of Occurrence:

Performance of Main Steam Line Code Safety Valves that required remedial action and corrective measures to prevent operation in a manner less conservative than that assumed in the accident analysis in the SAR or T.S. bases. Occurrence is reportable per T.S.6.9.1.8(i).

6. Coiditions Prior to Occurrence:

Steady-State Power Reactor Power 0 MWth Hot Standby X Net Output 0 MWe Cold Shutdown Percent of Full Power 0  %

Refueling Shutdown Load Changes During Routine Power Operation Routine Startup Operation Routine Shutdown Operation Other (specify)

7. Description of Occurrence:

The Main Steam Line C cde Safety Valves were being treated by increasing the Main Steam pressure to the valve lift setpoint, thus verifying proper adjustment and blowback. On four separate occasions, it..was discovered that the warn ring lockpin had broken. On 11/7/78 and 11/20/78, the lockpin broke on 2PSV1002. The lockpin in 2PSV1052 broke twice on 11/21/78.

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Reportabic Occurrence Report No. 50-368/79-020

8. Designation of Apparent Cause of Occurrence:

Design X Procedure bbnufacture Unusual Service Condition Including Environmental Installation /

Const ruction Component Failure (See Failure Data)

Operator Other (specify)

Failure was determined to be a result of the lockpin's fragility.

9. Analysis of Occurrence:

The lockpin function is to maintain the warn ring adjustment. With the lockpin broken, the relief setpoint for each valve could not be

1s sured. The failure occurred during Mode 3 operation, prior to initial criticality. The relieving capacity of the remaining safety valves always exceeded that required for safe operation, as dictated by T.S. Table 3.7.-l.

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Reportable Occurrence Report So. 50-368/79-020

10. Corrective Action:

Upon discovery of the failure, the lechpin was replaced with one of similar design until 11/21/78. At the end of testing, 2?SV1052, 2?SV1055 and 2?SV1056 vere gagged because lockpins had been used for replacements in other valves. On 11/28/78, the Icekpins were replaced in all of the Main Steas Line Code Safety Valves with one of a stronger and cere reliable design (see Sketch 1).

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11. Failure Data:

Other occurrences involving the Main Stea= Safety Valves are 50-368/79-019 and 50-368/78-010; however, they are not similar.

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