05000373/FIN-2014005-02
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Finding | |
|---|---|
| Title | Inappropriate Instructions Led to Failure of MSIV |
| Description | A finding of very low safety significance and associated non-cited violation of 10 CFR Part 50, Appendix B, Criterion V, Instructions, Procedures, and Drawings, was self-revealed for the licensees failure to establish instructions for an activity affecting quality that were appropriate to the circumstances. Specifically, when the Unit 2 C inboard main steam isolation valve (MSIV) failed shut due to a stem-to-disc separation on August 5, 2014, inspectors reviewed the circumstances leading to the failure and determined that engineering change (EC) 340595 was deficient. This EC was created in response to 2003 industry operating experience (OE) for the same failure mechanism (loss of pretension on the shaft-to-pilot-disc) at another facility, with the purpose of establishing inspection acceptance criteria to determine if the OE applied to LaSalle. The inspectors concluded that the acceptance criteria were inappropriate to the circumstances because they contained no guidance for identifying or dispositioning the actual failure mechanism reported in the OE. Even though two of the five MSIVs inspected at the time by the licensee displayed evidence of the OE-reported failure mechanism (loss of pretension), the acceptance criteria as written were satisfied, so the MSIVs passed their inspections and future rebuild activities were deferred based primarily on these false-negative inspection results. It was due to these deferrals that the August 5th failure occurred. All MSIV internals have since been rebuilt with a more robust design that is not susceptible to a loss of pretension failure, and a root cause evaluation was performed. The performance deficiency was determined to be more than minor because it was associated with the Initiating Events Cornerstone attribute of procedure quality and adversely affected the cornerstone objective of limiting the likelihood of events that upset plant stability and challenge critical safety functions during shutdown as well as power operations. Since the valve failure caused a reactor scram and loss of condenser as the normal heat sink due to the Group I MSIV isolation, a detailed risk evaluation was required. The RIII Senior Reactor Analysts (SRAs) performed a detailed risk evaluation using the NRCs Standardized Plant Analysis Risk model for LaSalle, version 8.24, and calculated a conditional core damage probability estimate of 8.4E-7, which represents a finding of very low safety significance, or Green. Because this performance deficiency occurred in 2003, no cross-cutting aspect was assigned because it was not considered current performance. |
| Site: | LaSalle  |
|---|---|
| Report | IR 05000373/2014005 Section 4OA3 |
| Date counted | Dec 31, 2014 (2014Q4) |
| Type: | NCV: Green |
| cornerstone | Initiating Events |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | W Schaup D Chyu D Lords D Mcneil J Cassidy J Robbins M Kunowski M Ziolkowski R Baker R Jickling R Ruiz R Winter R Zuffa T Go |
| Violation of: | 10 CFR 50 Appendix B Criterion V |
| INPO aspect | |
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Finding - LaSalle - IR 05000373/2014005 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (LaSalle) @ 2014Q4
Self-Identified List (LaSalle)
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