ML20084J347

Ro:On 720824,during Insp,Seven Suppression Chamber to Drywell Vacuum Breaker Valves Failed to Test Properly.Caused by Improper Setting of Remote Position Limit Switches.Shaft Key Screws Tightened

ML20084J347
Person / Time
Site:	Quad Cities
Issue date:	09/06/1972
From:	Palmer F COMMONWEALTH EDISON CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084J342	List: ML20084J347 ML20084J358
References
FAP-72-170, NUDOCS 8305120559
Download: ML20084J347 (3)

Text

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FAP-72-170 io P 'Ds. s.

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September 6, 1972 ~

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Mr. A. Giambusso - ' *

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Deputy Director for Reactor Projects Directorate of Licensing h '

U.S. Atomic Energy Commission -lg!

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Washington, D. C. 20545

Dear Mr. Giambusso:

Ref: Quad-Cities Nuclear Power Station _

Unit 2 - DPR-30 Appendix A Sections 1.0.A.2, 1.0.A.4, 3 7.A.4, and 6.6.B.3 m-_

The purpose of this letter is to report a condition _

relating to the operation of the station, in which, -

1 during a routine inspection seven Unit 2 suppression chamber to drywell vacuum breaker valves failed to test properly. Although the valves were not required to be operable at the time of the inspection, the valves may have been incapable of performing their required =

function during the previous period of reactor operation.

This condition was reported to you by telegram on August 29, 1972. -

DESCRIPTION OF INCIDENT ,

At 8: 30 a.m. on August 24, 1972 with Unit 2 reactor shutdown, preparations were made for a routine inspection of Unit 2 suppression chamber interior. Prior to torus .

en try , the suppression chamber to drywell vacuum breaker valves were exercised incidental to the scheduled inspection to verify valve operability. Several valves (2-1601-32A, 32D, 32E, 2-1601-33A, 33B, 33C, 33D) gave sporadic OPEN/ CLOSED indication during valve cycling iwith one valve (2-1601-32B) failing to actuate from the h -Y remote test panel. Subsequent visual inspection re-vealed that four valv.es which indicated CLOSED af ter the test were actually one inch or more from the full closed position. 2

-a INVESTIGATION m The suppression chamber to drywell vacuum breaker valves

• were taken out of service as a personnel safety precaution prior to conducting an inspection of the valves. At k at 8305120559 720927 PDR ADOCK 05000265 S PDR ggg M M I M rd e 4

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. O O Mr.' A. Giambusso September 6,1972 2:00 p.m. , the Unit 2 suppression chamber was entered and six valves were found open, four of which indicated closed (green light) at the remote test panel. The valves were the.n manually exercised open and closed which resulted in erratic valve " REST" position.

The suppression chamber to drywell vacuum breaker valves were subsequently disassembled and inspected. This inspection revealed that excessive friction due to the shaft key rubbing against a Teflon bushin6 and improper shaft alignnent was preventing successful valve actuation.

Futher investigation revealed improper setting of the remote position limit switches.

CORRECTIVE ACTION The suppression chamber to drywell vacuum breaker valves were disassembled and the " ALLEN" set screws which hold the shaft key in its proper position were tightened.

In addition, the valve seats on valves 2-1601-32D and 2-1601-32F were cut such that the valve disc could swing freely to its seat. The latter being required due to valve shaft realignment. Valve position indicatinz switches are being set to indicate an intermediate valve position as soon as the disc is cracked off its seat.

The vacuum breakers on Unit 1 will be inspected at the next opportunity for torus entry. Any modification made to the Unit 2 system as a result of this incident will also be made to Unit 1. This would also be reviewed for applicability to Dresden Units 2 and 3 CONCLUSIONS All valves were verified closed on April 7,1972 prior to establishing primary containment for the Unit 2 heatup following initial fuel loading. Since that time, the suppression chamber to drywell vacuum breaker valves were not actuated for test purposes until August 24, 1972.

, Due to false indication and excessive friction, however, lit cannot be positivel'y determined that the valves would

!have performed their intended function.

'The setpoint for the full closed position indicating switches is an interim setpoint for the indication and will be revised as necessary based on the results of the analysis requested by D. J. Skovholt's August 9,1972 letter on this subject. This evaluation of the limitations on open vacuum breakers is not complete at this time.

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Mr. A. Giambusso September 6, 1972 {

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It appears to COMMONWEALTl! EDISON CO?dPANY that the f -

design of the suppression chamber to drywell vacuum f l breaker valve counterweights required to provide positive 1, closing force could be improved. A design modification r is being developed through the original design organization =

1 pursuant to Criteria III of 10 CFR 50, Appendix B. ?_

Very truly yours , r e' --

COMMONWEALTH EDISON COMPANY Quad-Cities Nuclear Power Station '

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F. A. Palmer -m Superintendent I FAP/zm 2 E

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