05000395/FIN-2012007-03
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Finding | |
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| Title | Failure to Maintain One Train of Safe Shutdown Systems in Accordance with Appendix R Section III.G.a/III.G.3 |
| Description | The licensee identified a noncompliance with VCSNS Operating License Condition 2.C(18), Fire Protection System, for the failure to provide alternative shutdown capability for fires in certain areas where protection of SSCs did not satisfy the requirements of the FPP. Specifically, the licensee discovered that they did not meet the FPP requirement to ensure that alternative shutdown equipment remained operable and available. Description: During circuit analysis review in support of the NFPA 805 transition from the 10 CFR 50.48(b) licensing basis, the licensee discovered that a fire in the Control Building 412 North Chase (FA CB-4), Cable Spreading Room (FA CB-15), or Main Control Room (FA CB-17) could cause a hot short that could actuate a relay and result in the isolation of the B-train essential electrical bus (XSW1DB). Additionally, the licensee also discovered that a fire in FA CB-15 or FA CB-17 could cause a hot short that could result in the inability to start the B EDG using local controls. Per the licensees analyses, SSD for fires in these areas would be achieved by alternative shutdown methods. The licensees original circuit analysis and re-analysis considered the possibility of a fire induced open circuit in a current transformer (CT) circuit that connects a set of sensing CTs in XSW1DB to an ammeter in the MCR. However, the licensees circuit analyses failed to consider hot shorts to ground. As a part of the NFPA 805 transition review, this failure mode was considered. The licensee discovered that hot shorts to ground in this circuit could result in spurious actuation of Relay 51BN-1DB. This relay actuates another relay, which trips and locks out all incoming breakers to the 1DB switchgear, and the incoming main breakers for the 480V busses. The lockout relay also prevents the B EDG breaker from closing and powering XSW1DB. This ultimately results in a complete loss of power on XSW1DB. This condition has existed since initial plant startup. Additionally, the licensee discovered that a hot short in an EDG emergency start circuit could result in the unavailability of the B EDG. In 1985, a modification was performed to provide a de-energize to actuate feature in the B EDG start circuit. This feature would allow the diesel generator to start in the case of a fire-induced circuit fault to an EDG control circuit. A subsequent modification performed in 1992 inadvertently defeated the de-energize to actuate feature in the starting circuit, and created the possibility of a fireinduced hot short to this circuit that could result in the failure of the B EDG to automatically start. This hot short could also result in a blown fuse in the EDG start circuit, which would prevent the B EDG from being started locally. This condition has existed since September 1992, when the modification was implemented which inadvertently defeated the de-energize to actuate feature. Both of these scenarios could result in a loss of power on the B ESF bus. For alternative shutdown, the licensees FEPs utilize a self-induced station blackout (SISBO) methodology, where the A ESF bus is disabled, the B ESF bus is credited with being available to provide power to safely shutdown the plant. Therefore, hot shorts described in these scenarios would render the credited power source unavailable to provide power to multiple components credited for alternative SSD. The licensee determined that these conditions were caused by human error during the original circuit analyses, and a less than adequate design change/configuration management process. Upon discovery, the licensee implemented compensatory measures, including posting roving fire watches in FAs of concern, installing temporary jumpers, and revising FEPs. The licensee also committed to restoring compliance by implementing design changes, as a part of the NFPA 805 transition process. |
| Site: | Summer  |
|---|---|
| Report | IR 05000395/2012007 Section 4OA3 |
| Date counted | Sep 30, 2012 (2012Q3) |
| Type: | Violation: Severity level Enforcement Discretion |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | D Mas G Wiseman J Montgomery L Suggs M King M Thomas |
| INPO aspect | |
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Finding - Summer - IR 05000395/2012007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Summer) @ 2012Q3
Self-Identified List (Summer)
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