05000289/FIN-2010009-03
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Finding | |
|---|---|
| Title | Multiple MSSVs test failures due to improper evaluation of Operating Experience |
| Description | A self-revealing Green NCV of TMI Technical Specification (TS) 3.4.1.2.3 was identified for having greater than three main steam safety valves (MSSVs) inoperable for greater than the allowed outage time with reactor power greater than 5%. MSSV testing prior to the 2009 refueling outage identified that six MSSVs failed the lift point test and were subsequently declared inoperable. All six valves failed by lifting above the ASME limit of +/- 3% of designed setpoint. Five of these six valves exhibited signs of oxide binding, a known failure mechanism for MSSVs and each of the valves had been refurbished during the 2007 refueling outage. Exelon had fleet and industry information about the oxide binding failure mechanism available in 2006 at the time the refurbishment method was selected for the 2007 TMI outage. This refurbishment method included a decision to machine hone the MSSV seat to a mirror finish. This decision created the conditions for oxide binding and resulted in each of the valves failing their lift tests and being declared inoperable when tested in 2009. Exelon has changed its refurbishment process to preclude this error in the future, refurbished all of the affected valves, submitted a required licensee event report (LER), and entered the issue into the CAP. The decision in 2006 to machine hone the MSSV seat to a mirror finish, which established the conditions for oxide binding, was a performance deficiency that was within Exelon\'s ability to foresee and prevent due to available operational experience. This performance deficiency is more than minor because it affected the Equipment Performance Aspect of the Mitigating Systems Cornerstone Objective of ensuring the operability, availability, and reliability of systems designed to mitigate transients and prevent core damage. The team assessed this finding in accordance with IMC 0609, Attachment 4, Phase 1 - \"Initial Screening and Characterization of Findings,\" and determined that it was of very low safety significance (Green) since it did not result in a loss of any system safety function. This finding was determined to not have a cross-cutting aspect because the performance deficiency occurred in 2006 and was no longer indicative of current licensee performance. Specifically, Exelon made changes to their MSSV refurbishment program in 2008 which implemented the available OE, prior to discovery of the 2009 failures. |
| Site: | Three Mile Island  |
|---|---|
| Report | IR 05000289/2010009 Section 4OA2 |
| Date counted | Sep 30, 2010 (2010Q3) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | Self-revealing |
| Inspection Procedure: | IP 71152 |
| Inspectors (proximate) | D Orr J Brand R Bellamy A Rao |
| INPO aspect | |
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Finding - Three Mile Island - IR 05000289/2010009 | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Three Mile Island) @ 2010Q3
Self-Identified List (Three Mile Island)
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