05000261/FIN-2010012-01
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Finding | |
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| Title | Procedure Violation for Overriding Feedwater Isolation Safety Function in Mode 3 |
| Description | A self-revealing Green NCV of Technical Specification (TS) 5.4.1, Procedures, was identified when the licensee bypassed the feedwater isolation safety function, in Mode 3, a condition prohibited by TS and an action contrary to procedural requirements. On October 7, 2010, Unit 2 was in Mode 3 after a reactor trip that occurred earlier in the day. Steam generator feedwater was being supplied by the auxiliary feedwater (AFW) system and the main feedwater system was not running because of an automatic feedwater isolation, which occurred shortly after the reactor trip due to high C S/G water level. Contrary to procedure OP-403, Feedwater System, control room operators overrode the feedwater isolation safety function by placing the feedwater logic switches in Override/Reset, and leaving them in that position for three hours and twenty minutes. Upon realization of the error, licensee operators isolated S/G feed flow, placed the feedwater isolation logic switches in the Normal position, and restarted S/G feed flow with the AFW system. This issue was entered into the licensees CAP as AR 425643425643 The failure to operate the feedwater isolation logic switches in accordance with plant procedures is a performance deficiency. The finding is more than minor because it affects the human performance attribute of the Mitigating Systems cornerstone and the objective of ensuring the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences (i.e. core damage). Specifically, the finding affected the ability for the feedwater isolation (FWIS) to isolate the S/Gs and prevent overfeeding/overcooling events. The inspectors evaluated this finding using IMC 0609, Significance Determination Process Phase 1 screening and determined that the finding represented a complete loss of the FWIS function which required further evaluation under SDP Phase 2. The Robinson Phase 2 Pre-Solved SDP Worksheet and Phase 2 SDP Notebook did not include the FWIS function therefore a phase 3 SDP analysis was performed by a regional Senior Regional Analyst (SRA) in accordance with NRC IMC 0609. The plant was already shutdown prior to the performance deficiency so Anticipated Transients Without Scram scenarios would not be valid. The impact of the loss of the FWIS function would be that the S/Gs would not be isolated on Hi-Hi S/G water level and plant overfeed scenarios could result in Safety Injection initiation on low Reactor Coolant System (RCS) pressure and potential overfill/moisture carryover scenarios could overspeed the turbine driven AFW pump. The phase 3 analysis considered a potential overcooling and safety injection scenario using the licensees full scope Robinson Probabilistic Risk Assessment (PRA) model data and a potential moisture carryover induced overfeed scenario causing a loss of the turbine driven AFW pump on overspeed using the NRC Robinson Standardized Plant Analysis Risk (SPAR) model and data. The core damage frequency increase for both scenarios was <1E-6 per year. The risk was mitigated by the short exposure period. The finding is characterized as Green, a finding of very low safety significance. The finding has a cross-cutting aspect in the Human Performance area, Decision Making component because the licensee failed to make a safety-significant or risk-significant decision using a systematic process to ensure safety was maintained when faced with uncertain or unexpected plant conditions. Specifically, the licensee intentionally bypassed the safety function of feedwater isolation instrumentation while it was required with the reactor plant in Mode 3. |
| Site: | Robinson  |
|---|---|
| Report | IR 05000261/2010012 Section 4OA5 |
| Date counted | Dec 31, 2010 (2010Q4) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | Self-revealing |
| Inspection Procedure: | IP 93812 |
| Inspectors (proximate) | F Ehrhardt S Rose R Musser |
| Violation of: | Technical Specification |
| CCA | H.13, Consistent Process |
| INPO aspect | DM.1 |
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Finding - Robinson - IR 05000261/2010012 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Robinson) @ 2010Q4
Self-Identified List (Robinson)
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