05000247/LER-2010-004

LER-2010-004, Plant Operation Outside Technical Specifications Due to a Leak in the Reactor Coolant Pressure Boundary

Indian Point 2
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2472010004R00 - NRC Website

Note:

� The Energy Industry Identification System Codes are identified within the brackets {}.

DESCRIPTION OF EVENT

On March 18, 2010, at approximately 11:14 hours, while shutdown for refueling, boron accumulation was noted (there was no sign of wetness but rather white, dry boron which indicated that the leak rate was small) in the reactor coolant pressure boundary (RCPB) {AB} on three quarter inch pipe 76 upstream of valve 256B {V}. This check valve is on the 22 Reactor Coolant Pump (RCP) {P} seal {SEAL} bypass line. On April 5, 2010 at approximately 8:42 am the event was independently reviewed and determined to be reportable. Based on the amount of boron, a conclusion was reached that this condition could have existed during plant operation and therefore the plant could have been operating contrary to Technical Specification (TS) TS 3.4.13. This event was recorded in the Indian Point Energy Center corrective action program (CAP) as CR-IP2-2010-01631.

During boric acid walk downs performed during 2R19, boron was identified adjacent to valve 256B. After cleaning was performed, a surface examination was performed on the socket weld attaching the upstream three quarter inch pipe to valve 256B. This surface examination identified a five-sixteenths inch diameter rounded indication which appeared to be the source of the leakage. This indication was repaired and the post repair examination confirmed that the indication had been removed and the repaired area was acceptable.

Since the indication was removed by grinding, a failure analysis was not performed to identify the exact cause of the indication. However, both internal and external operating experience with similar defects strongly suggests that the cause of the through wall indication was a minor weld defect introduced at the time of system construction which propagated through wall as a result of the system loading conditions during plant operations. Literature documents that forging, casting, welding and other material fabrication defects can propagate through the wall of the component and result in leakage after long periods of service. The predominant driver for this propagation is the service induced loads caused by local stress concentrations as well as local pressure and thermal loads caused by local geometry discontinuities.

The original weld defect would not have been repaired at the time of construction if the indication was within the flaw allowable standards and, since the indication was not removed, it can be concluded that it was accepted during the original inspection (there is no documented evidence of the original inspection results). The defect would not have been discovered by inservice inspection since NDE on three quarter inch welds is not required.

The balance of the boric acid walk downs performed on systems which carry borated water during plant operations, identified no other leaks as a result of a through wall flaw in a pipe or in a component.