05000317/FIN-2006012-01
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Finding | |
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| Title | Failure to Adequately Control the Design of the Setpoints for 1A EDG Feeder Breaker for Essential Support Systems |
| Description | An apparent violation of 10 CFR 50, Appendix B, Criterion III (Design Control) was identified involving the failure to ensure an adequate trip setpoint for the electrical circuit breaker that supplies the 1A EDG support systems. An SDP Phase 3 risk analysis determined that the failure to account for possible combinations of 1A EDG support equipment operation in the short-time over-current trip setpoint for the supply breaker to 1MCC123 was preliminarily of low to moderate safety significance. Specifically, the short-time over-current trip setpoint was set too low and it did not account for the in-rush current associated with the possible combinations of equipment that could start and operate to support the 1A EDG following a loss of offsite power (LOOP). This low setpoint, combined with normal setpoint drift, resulted in substantial periods where the 1A EDG would not have been able to perform its safety function, because the support system supply circuit breaker would have tripped open inappropriately. Calvert Cliffs took immediate action to correct the breaker setpoint and evaluate other potential deficiencies of a similar nature. This issue was entered into the corrective action program at Calvert Cliffs for resolution. The finding was more than minor because it affected the Mitigating Systems Cornerstone objective to ensure the availability and reliability of systems (i.e., emergency AC power) that respond to initiating events to prevent undesirable consequences, and its related attribute for design control. The \\\"0C\\\" Station Blackout Diesel Generator (a non-safety related, but risk-important power source) and the breaker for its support systems were similarly affected by the performance deficiency. SDP Phase 1, Phase 2, and Phase 3 assessments were used to evaluate the risk significance of this finding. The Phase 1 screening required performance of a Phase 2 evaluation because the finding represented a loss of safety function of a single train, for greater than its allowed outage time. The Technical Specification (TS) allowed outage time is 14 days for a single EDG. To assess the full significance both the Phase 2 and Phase 3 analyzes assumed a 5407 hour0.0626 days <br />1.502 hours <br />0.00894 weeks <br />0.00206 months <br /> exposure for the 1A EDG being unable to perform its safety function and an additional 6.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> where both the 1A EDG and the 0C DG would not have been able to perform their required functions (the 0C EDG had less instrument drift). The Region I senior reactor analyst (SRA) conducted a Phase 3 Risk Assessment, to refine the Phase 2 analysis and to incorporate external events and recovery credit. The Phase 3 analysis for internal and external initiating events, using the above assumptions and licensee risk information, determined a )CDF of approximately 1 in 150,000 years of operation (mid E-6 per year range) for both internal and external events, with no associated increase in large early release frequency (LERF). The risk of the 1A EDG exposure time dominated the analysis by several orders of magnitude over the risk of the concurrent 1A EDG and 0C DG exposure time. A large fire in the turbine building, which causes a loss of offsite power, was the dominating initiating event. |
| Site: | Calvert Cliffs  |
|---|---|
| Report | IR 05000317/2006012 Section 4OA3 |
| Date counted | Sep 30, 2006 (2006Q3) |
| Type: | Violation: White |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | R Pascarelli R Summers S Collins A Blough B Holian B Mcdermott D Holody K Farrarb Mcdermottc Cahill J Giessner M Davis |
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Finding - Calvert Cliffs - IR 05000317/2006012 | |||||||||
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Finding List (Calvert Cliffs) @ 2006Q3
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