ML19343C229

AO 50-219/74/34:on 740529,coolant Leakage Found in Area of Incore Flux Monitor Reactor Vessel Housing at Core Coordinate 28-05.Cause Undetermined.Insp Program Developed to Examine Incore Flux Monitor Tube from Below Vessel

ML19343C229
Person / Time
Site:	Oyster Creek
Issue date:	06/07/1974
From:	JERSEY CENTRAL POWER & LIGHT CO.
To:
References
AO-50-219-74-34, NUDOCS 8103040530
Download: ML19343C229 (2)

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OYSTER CREEK NUCLEAR GENERATING STATION FORKED RIVER, NEW JERSEY 08731 Abnormal Occurrence Report No. 50-219/74/34 Report Date June 7, 1974 Occurrence Date May 29, 1974 Identification of Occurrence Indications of coolant leakage existing in the area of an incore flux monitor reactor vessel housing located at core coordinate 28-05. This event is considered to be an abnormal occurrence as defined in the Technical Specifications, paragraph 1.15E.

Conditions Prior to Occurrence The plant was shut down for refueling. The reactor was in the RErdEL mode during a hydrostatic test at 850 psig precsure and with coolar.c temperature approximately 155'F.

Description of Occurrence On Tuesday, M y 28, 1974, during a scheduled reactor vessel hydrostatic test to inspect the pressure boundary following refueling maintenance activities, leakage was observed in the vicinity of an incore flux monitor tube located at the bottom of the reactor vessel. Further investigation conducted on Wednesday, May 29, 1974, showed evidence of possible laakage in the area of an incore flux monitor housing penetration located in the reactor vessel bottom head. A second hydro-static test was conducted at a pressure of 850 psig at r.pproximately 7:00 p.m.

on .\by 29,1974, whereupon, water was observed leaking between the monitor housing and the reactor vessel. The leakage was measured under the conditions of 850 psig with a temperature of 164*F, and calculated to be on the order of approximately 0.02 gallor.s per hour.

Apparent Cause of Occurrence The cause of this event has yet to be determined.

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Analysis of Occurrence As stated in FDSAR Amendment No. 37, a postulated failure of the flux monitor.

tube would result in vessel leakage at a rate which would not cause excessive cladding temperatures and for which core reflooding is possible by engineered safety features. This situation is less severe than the design basis accident.

To determine the consequences of a weld failure at a housing for an incore -

monitor tube, it is assumed that the weld between the housing and the reactor vessel bottom head fails, allowing the housing and the incore monitor tube to be ejected from the vessel. The hole provided in the bottom head for the housing has a diameter of two inches. This is -the assumed break size. The-hole has a break area of .0218 ft2 . Assuming worst conditions, this results in peak clad temperatures less than 1000*F, as updated in FDSAR Amendment No. 67. This value is well within acceptable limits of the applicable ECCS criteria.

Corrective Action An inspection program was developed by the plant staff and Jersey Central Power 6 Light Company management and concurred with by the nuclear steam supply system i vendor, the reactor vessel manufacturer, and an engineering consulting firm.

The program to examine the incore flux monitor tube from below the ' reactor vessel is as follows:

, 1. Visual inspection with a borescope

2. Leak test with helium using a mass-spectrometer

3. UT inspection

4. Pressure test of the reactor vessel

5. Chemical and physical analys;s of the water in the tdbe, the crud in the tube, and the buildup around the tube.

l In addition, an eddy current inspection was later added to this program to be performed following the UT inspection.

Recommendations for repair will be forthcoming pending a complete review and evaluation of the results of this program by the Plant Operations Review Committee.

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