ENS 46997

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v t e ENS Event
20:11 Jun 27, 2011
Title	Appendix R Analyses Fails to Recognize Hot-Short Failure Resulting in the Loss of an Essential Electrical Bus
Event Description	The following Part 21 report was received via fax: 10 CFR 21: Appendix R analyses conducted for Virgil C. Summer Nuclear Station (VCSNS) failed to identify that a fire-induced hot-short failure in an ammeter circuit would result in a loss of the B-train 7.2KV essential electrical bus (XSW1DB). Appendix R analyses performed by Gilbert/Commonwealth (now Worley Parsons) in the early 1980s failed to recognize the possibility of a fire-induced hot-short condition in a circuit that was identified as being required for safe shutdown. This circuit connects a set of sensing current transformers (CTs) to an ammeter on the Main Control Board, and provides over-current sensing for an over-current relay. Gilbert/Commonwealth recognized that a fire-induced open circuit in this ammeter circuit would result in damage to, or a fire in, the B-train 7.2kV essential switchgear. Thyrite protectors were added to the circuit to protect the CTs from this open circuit condition as part of the Appendix R analysis. However, this analysis and resolution failed to consider the hot-short-to-ground failure mode. Current from a hot-short could flow through the ammeters, or neutral conductor, and then through the bus neutral over-current relay to ground. This could actuate the over-current relay, which in turn would actuate a lock-out relay and trip all incoming breakers to bus XSW1DB. This bus provides credited B-train power to safe-shutdown components credited for this scenario. The Appendix R analyses conducted for VCSNS by Gilbert/Commonwealth did not address the hot-short scenario and is considered to be a defect, or omission. reportable under 10 CFR 21. This condition was identified during the circuit analysis review for transitioning the Appendix R Fire Protection Program to NFPA 805 and was reported to the NRC as an unanalyzed condition on 05/03/2011 (see Event Notification 46811). Corrective actions have been taken to address this issue. The licensee informed the NRC Resident Inspector. * * UPDATE FROM JOE MARSDEN TO MARK ABRAMOVITZ ON 6/30/2011 AT 1643 * * * Worley Parsons Investigation Results: Although this design was not a generic or standard design, Worley Parsons performed further evaluation, including extent of condition, for other Nuclear Power Plants that Worley Parsons performed the original design and performed Appendix R Compliance Review/Modifications. Five plants were identified as follows: 1) Crystal River 3: Worley Parsons discussed the issue with Progress Energy and jointly concluded that Crystal River 3 is not impacted because their corresponding current transformer circuit design has a different configuration. The circuit design is not generic or programmatic. 2) TMI Unit 1: TMI is not impacted because their corresponding current transformer circuit design has a different configuration. The circuit design is not generic or programmatic. 3) Perry: The Appendix R Compliance Review was accomplished by a team of Worley Parsons and others. Since Worley Parsons was involved with the Appendix R analysis and the affected electrical drawings are not readily available at Worley Parsons, it was concluded that Worley Parsons could not complete the evaluation to determine if the Perry design condition could cause a substantial safety hazard. Worley Parsons issued letter PNPP-O-CO-011-WCLT-0001 to the Perry Design Engineering Manager, recommending Perry to complete the evaluation pursuant to 10CFR21.21(a). 4) V.C. Summer: V.C. Summer is the subject plant and is impacted. VC. Summer is issuing LER #2011-001-00, which constitutes the Part 21 Notification for this design defect, or omission. 5) R.E. Ginna: Worley Parsons did not perform the Appendix R analysis for Ginna. Corrective Action: V.C. Summer has implemented immediate compensatory measures for this condition until a permanent solution is identified. A root cause analysis was jointly performed with V.C. Summer. The root cause analysis and Worley Parsons corrective action program review considered this an isolated incident due to human error. No programmatic/procedure corrective actions were identified due to the historical nature of the issue. Actions to preclude recurrence: Human performance issues from this event will be communicated to the Worley Parsons Nuclear Engineering staff under our corrective action and lessons learned program. Notified R1DO (Welling), R2DO (Franke), and R3DO (Lipa). Notified the Part 21 Group via e-mail.

ENS 46997 +/-
Where
Summer South Carolina (NRC Region 2)
Reporting

10 CFR 21.21
Time - Person (Reporting Time:+37.63 h1.568 days <br />0.224 weeks <br />0.0515 months <br />)
Opened:	Bruce Thompson 09:49 Jun 29, 2011
NRC Officer:	Steve Sandin
Last Updated:	Jun 30, 2011
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Summer with 10 CFR 21.21
WEEKMONTHYEAR2011-06-27T20:11:00 [Table view]
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