ML19317F396

Unusual Event 287/75-10:on 751005,weld Failed on Sample Line from LPIS Cooler.Caused by Cavitation at High Flow Rates in Butterfly Control Valve 3LP-12.3A LPIS Train Isolated,Weld Repaired & to Be Dye Penetrant Tested

ML19317F396
Person / Time
Site:	Oconee
Issue date:	11/13/1975
From:	DUKE POWER CO.
To:
Shared Package
ML19317F388	List: ML19317F387 ML19317F396
References
RO-287-75-10, NUDOCS 8001140645
Download: ML19317F396 (2)

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' DUKE POWER COMPANY' OCONEE NUCLEAR STATION i

1 Report No.: 'UE-287/75-10 Report Date: November 13, 1975

- Event-Dato: . October.5, 1975 Facility: ~Oconee. Unit 3',. Seneca,~ South Carolina ,

'dentification'of Event: Weld failure on sample line from Low Pressure I

Injection System cooler

! Conditions Prior to Event: Unit at cold shutdown Description of Event:

On October.5, 1975, while the'Oconee Unir 3 3A LPI train was in the decay heat removal mode,

a.1" sample line from the discharge of the 3A LPI j cooler separated from the LPI cooler discharge line. The 3A cooler was 4 isolated and decay heat removal was continued with the 3B decay heat  !

" cooler.

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Designation of' Apparent'Cause of Event: .

This event.was.apparently caused by cavitation occurring at high flow

'l . rates in the butterfly control valve 3LP-12 located in the cooler discharge line. This'. cavitation caused the line to vibrate excessively during .

operationiin the' decay heat removal mode and consequently _resulted in a i e

t weld: failure in the-sample line.

Analysis of Event:-

This event involved the' failure of a 1" sample line while the unit was in a cold. shutdown condition. ' The redundant' LPI cooler, 3B, was not. af fected

. and .was operated- to provide : sufficient decay heat removal while the 3A LPI i  : train ~was isolated and repairs completed. It is concluded that- the health

and safety of the public;was_unaffecter by this event.

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~ Corrective' Action:

UThe 3A 'LPI train was isolated,ithe weld repaired, and dye penetrant testing was performed to assure systemLintegrity. In. addition, several representative welds, ' including corresponding welds in Units -I and' 2 wil1~ be dye penetrant

, tested.' This; testing'will.be completed byLJatuary 15,;1976.

The causative' cavitation problem:has existed in the LPI cooler discharge l

. : lines for~allfof the.0conee units. The problem was initially experienced l

- ' with . valves 1LP-12 and :-14 and 2LP.-12 ^and -14,- located in the LPI cooler

discharge,linesjof(Units 11;and;2,-and occurred under conditions'of low

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coolant flow through these lines. Af ter careful review, a decision was made to replace these valves with valves of a globe body design which would eliminate

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the cavitation problem. These valves for Units 1 and 2 were ordered in June, 1975. It was not considered that this cavitation problem would occur in Unit 2 LPI coolers since the piping arrangement differs from Units 1 and 2 and valves 3LP-12 and'-14 are of a different design, intended to alleviate the cavitation effects as experienced in Units 1 and 2. A cavitation problem was experienced with Unit 3, however, but differed from that experienced with Units 1 and 2 since it occurred at high rather than at low flow rates.

Currently, after performing a comprehensive evaluation of this incident, it has been concluded that replacement valves identical to those being procured for Units 1 and 2 are necessary to alleviate the cavitation problem in Unit 3.

The procurement of these valves is being finalized.

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