05000237/LER-1975-052, For Dresden Unit 2 Regarding a Report of Rapid Closure of Unit-2 Main Steam Isolation Valve 203-1C

For Dresden Unit 2 Regarding a Report of Rapid Closure of Unit-2 Main Steam Isolation Valve 203-1C

ML17252B459
Person / Time
Site:	Dresden
Issue date:	11/20/1975
From:	Stephenson B Commonwealth Edison Co
To:	James Keppler NRC/RGN-III
References
BBS Ltr. #769-75 LER 75-052-00
Download: ML17252B459 (2)

LER-1975-052, For Dresden Unit 2 Regarding a Report of Rapid Closure of Unit-2 Main Steam Isolation Valve 203-1C

Event date:
Report date:
2371975052R00 - NRC Website

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Commonw6th Edison One First Nai-Plaza, ~htGego, Illinois Address Reply to: Post Office Box 767 Chicago, lllinoi~ 60690 BBS Ltr. #769-75 Mr~ James G. Keppler, Regional Director Directorate of Regulatory Op~ration - Region IiI U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137

SUBJECT:

REPORT OF ABNORMAL OCCURRENCE PER SECTION.6.6.A OF THE TECHNICAL SPECIFICATIONS RAPID CLOSURE OF UNIT-2 MAIN STEAM ISOLATION VALVE 203-lC

References:

1)

Regulatory G~ide-1.16 Rev. 1 Appendix A

2)

Notification of Region III of U.S. Nuclear Regulatory Connnissi_on Telephone_:. Region III Headquarters, Duty Office, 0855 hours0.0099 days <br />0.238 hours <br />0.00141 weeks <br />3.253275e-4 months <br /> on November 16, 1975 Telegram:. J. Keppler, 12-SO hours on Report Number:

50-237/197--5..:.52 Report Date:

November 20:, 1975 Occurrence Date:

November 16, 1975

.IDENTIFICATION OF OCCURRENCE Main steam isolation valve AO 2-203-lC closed in iess than 3.0 seconds, which is contrary to section 3.7.-D.l of the Technical Specifications.

CONDITIONS PRIOR TO OCCURRENCE Unit-2 was in the Run mode at a power level of 428 MWt and 103 MWe.

Quarterly surveillance testi~g of the main steam isolation valves was in progress.

DESCRIPTION OF OCCURRENCE At approximately 0330 hours0.00382 days <br />0.0917 hours <br />5.456349e-4 weeks <br />1.25565e-4 months <br /> on November 16, 1975, main steam isolation valve 203-lC exhibited a closure time of 2.7 seconds.

Technical Specifications require that for closure time *t, 3.0 sec.. 2_ t 2_ 5.0 sec.

The valve was left in the isolated position, and the unit was subsequently shut down.

13509

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,n Mr. James G. Keppl.

.J~rl 41tNovember 20, 1975

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DESIGNATION OF APPARENT CAUSE OF OCCURRENCE (Component Failure)

Inspection of valve 203-lC revealed that the hydraulic bleed-off valve was out of adjustment.

The bleed-off valve controls the rate of oil exchange across th~ valve operator piston, thus controlling the valve's rate of closure.

The bleed-off valve adjustment discrepancy was attributed to normal valve wear.

ANALYSIS OF OCCURRENCE All eight main steam isolation valves had been satisfactorily tested on September 9, 1975.

Had a reactor scram occurred while valve 203-lC was out_

of adj.ustment, the resultant premature isolation of the "C" main steam line would have.:presented minimal safety implications.

The remaining three steam lines would have effectively equalized any pressure spike, thereby'precluding the 1wssibility of a significant transient within the reactor vessel.. This occurrence did not endanger plant perso~nel or the general public.

• CORRECTIVE ACTION Following shutdown of the unit, the bleed-off valve on 203-lC w~s readjusted to bring the valve closure time within specifications.

.i\\t 1720 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.5446e-4 months <br />.on November 16,.valve. 203-lC was successfully tested three t'imes, with an

.average closure time of. 3.6 seconds.

The valve was then returned to service in preparation.for _unit start-up.

. FAILURE DATA Four similar isolation valve timing failures have occurred at Dresden since 1970.

The main steam isolation valve~.are manufactured *by Crane,.Val 1/e -~Co; ;. :*,.

air-operate_d, ZO" Y-pattern. globe yalves,

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