ML19289E730

LER 79-001/03L-1 on 790110:through Wall Leak Near Reactor Water Cleanup Sys Suction Piping Noted.Caused by Cracks in Weld Neck Due to Intergranular Stress Corrosion.Repairs Made & Sys Returned to Svc

ML19289E730
Person / Time
Site:	Vermont Yankee
Issue date:	05/23/1979
From:	Conway W VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19289E728	List: ML19289E727 ML19289E730
References
LER-79-001-03L, LER-79-1-3L, NUDOCS 7905290040
Download: ML19289E730 (2)

Text

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LER 79-01/3L, Rev. 1 VTVYS1 05000271 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES During normal operation, while performing routine maintenance, leakage was observed adjacent to a 2" flange on the Reactor Water Cleanup System suction piping. Investigation revealed a through wall leak near the piping weld between the 2" flange and the adjoining tee. Further invest-igation revealed a through wall leak in the spare nozzle of the Electro Chemical Potential Autoclave located upstream of the 2" flange. The Reactor Cleanup System was secured, the flange replaced, and the spare nozzle connection repair welded.

Conductivity monitoring of main coolant was shifted *.o the recircu-lation loop sample point during the repairs. The RWCU System was returned to service approximately 19 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br /> after the discovery. Reactor water chem-istry was maintained within Tech. Spec. limits and there were no conse-quences to the health and safety of the public. A similar incident was reported as RO 77-22/IP.

CAUSE DESCRIPTION AND CORRECTIVE ACTIONS The cause of the cracks in the Reactor Water Cleanup weld neck flange is Intergranular Stress Corrosion. The cracks initiated on the inside surface parallel to the weld in the sensitized heat affected zone adjacent to the weld and were intergranular in nature. One crack completely pene-trated the wall of the flange. No fatigue striations were found. The appearance of the cracking indicates typical boiling water reactor type stress - corrosion cracking with residual stresses froc welding or possibly slow cyclic bending stresses as being the scurce of the tensile stress.

'.2043 274'.