05000219/LER-2014-004
| Oyster Creek, Unit 1 | |
| Event date: | 09-18-2014 |
|---|---|
| Report date: | 11-17-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2192014004R00 - NRC Website | |
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Description of Event
On September 18, 2014, during refueling outage 01R25 with the unit in cold shutdown, as-found LLRTs were performed on the main steam lines. The as-found LLRT of MSIV NSO3B (V-1-8) failed to meet the acceptance criteria of Technical Specification 4.5.D.2. The acceptance criteria is less than or equal to 11.9 scfh at 20 (+3/-0) psig. The actual measured leakage was 16 scfh at 20.3 psig.
The valve was disassembled, inspected, the poppet assembly was replaced, and the valve seat was machined. The cause of failure was identified to be due to material wear on the poppet assembly and the valve seat. An as-left LLRT was performed with an acceptable reading of 0.621 scfh at a test pressure of 20.3 psig.
Analysis of Event
The MSIVs are containment isolation valves designed to minimize coolant loss from the vessel, and the resultant offsite dose, in the event of a main steam line accident. There are two main steam lines with 2 MSIVs in series in each line. The acceptance criteria, for these valves, is less than or equal to 11.9 scfh when tested at greater than or equal to 20 (+3/-0) psig. Exceeding the leakage limits specified in the Technical Specifications could result in unacceptable dose rates downstream of the MSIVs during an accident.
The safety significance of this event is considered minimal. The leakage past NSO3B (V-1-8) would have been limited by the leak rate of the outboard MSIV NSO4B (V-1-10) in the same header, which met the LLRT acceptance criteria of Technical Specification 4.5.D.2 when tested in 01R25. The leak rate of NSO4B provided adequate margin between projected offsite dose and 10 CFR 100 guidelines.
Cause of Event
The cause of failure was due to material wear on the poppet and the valve seat.
Corrective Actions
The valve was disassembled, inspected, the poppet assembly was replaced, and the valve seat was machined.
The as-left LLRT on MSIV NSO3B was successfully completed.
Previous Occurrences
LER-1006-003-00, Local Leak Rate Test Results in Excess of Technical Specifications Component Data Components IEEE 805 System ID IEEE 803A Function
MSIV SB ISV