ML11182A917

Part 21 Notification, Appendix R Analyses Fails to Recognize Hot-Short Failure Resulting in the Loss of an Essential Electrical Bus

ML11182A917
Person / Time
Site:	Summer
Issue date:	06/29/2011
From:	Thompson B South Carolina Electric & Gas Co
To:	Office of Nuclear Reactor Regulation
References
Download: ML11182A917 (3)

Text

06129120l11 U.S. Nuclear Regulatory Commission OperationsCenter Event Report Pa,-e I Power Reactor Event# 46997 Site: SUMMER Notification Date / Time: 06/29/2011 09:49 (EDT)

Unit: 1 Region: 2 State: SC Event Date/ Time: 06/27/2011 16:11 (EDT)

Reactor Type: [1] W-3-LP Last Modification: 06/29/2011 Containment Type: DRY AMB NRC Notified by: BRUCE THOMPSON Notifications: MARK FRANKE R2DO HQ Ops Officer: STEVE SANDIN PART 21 GP (email) NRR Emergency Class: NON EMERGENCY 10 CFR Section:

21.21 UNSPECIFIED PARAGRAPH Unit Scram Code RX Crit Init Power Initial RX Mode Curr Power Current RX Mode N Yes 1 100 Power Operation 100 Power Operation APPENDIX R ANALYSES FAILS TO RECOGNIZE HOT-SHORT FAILURE RESULTING IN THE LOSS OF AN ESSENTIAL ELECTRICAL BUS 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 (XSW1 DB).

"Appendix R analyses performed by Gilbert/Commonwealth (now WorleyParsons) in the early 1980sfailed 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 XSW1 DB. 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

06/29/2011 U.S. Nuclear Regulatory Commission Operations Center Event Report Paze2 Power Reactor Event # 46997 Program to NFPA 805 and was reported to the NRC as an unanalyzed condition on 05/03/2011 (see Event Notification No. 46811). Corrective actions have been taken to address this issue."

The licensee informed the NRC Resident Inspector.

PAGE 1 OF 2 NRC FORM 361 U.S. NUCLEAR REGULATORY COMMISSION (12-2000) REACTOR PLANT OPERATIONS CENTER EVENT NOTIFICATION WORKSHEET EN# 7 NRC OPERATION TELEPHONE NUMBER: PRIMARY - 301-816-5100 or 800-532-3469", BACKUPS - [1st] 301-951-0550 or 800-449-3694W, (2ndl 301-415-0550 and [3rdl 301-415-0553 *Licensees who maintain their own ETS are pDrovided these teleDhone numbers.

NOTIFICATION TIME FACILITY OR ORGANIZATION UNIT NAME OF CALLER CALL BACK #

(3 ý I\ VC Summer Nuclear Station 1 Bruce Thompson (803) 931-5042 EVENT TiME &ZONE EVENT DATE POWERIMfviO[ BEFORE POWERJMODE AFTER

(,.vt kIG ý2- 100% Model1 100% ModelI EVENT CLASSIFICATIONS 1-Hr. Non-Emergency 10 CFR 50.72(b)(1) (v)(A) Safe SID Capabilty AINA GENERAL EMERGENCY GEI/AAEC TS Deviation ADV (vXB) RHR Cagiity AINB SITE AREA EMERGNCY SrAAEC 4-Hr. Non-Emergency 10 CFR 50.72(b)(2) (vXC) Control of Red Release AD'C ALERT ALE/AAEC (i) TS Required SID ASHU (vXD) Accident Mitigation AJ'D UNUSUAL EVENT UNLVAAEC (iv)(A) ECCS Disdchage to RCS ACCS (xni) Offsita Medical NVED 50.72 NON-EMERGENCY (see next columns) _ (iv)(B) RPS Actuation (scram) ARPS (xa) Loss Ccmm/Asat/Resp A(MX PHYSICAL SECURITY (73.71) (1))) (Ax) Offsita Notificatlon A 60-Day Optional 10 CFR 50.73(a)(1)

MATERLUALEXPOSURE B7?? 8-Hr. Non-Emergency 10 CFR 50.72(b)(3) Inval Specied System Actuation FITNESS FOR DUTY HFIT (ii)(A) Degraded Condition ADM Other Unspecified Requirement (Identify)

OIERU PECFE RECUT. (see last column) (ii)(B) Unanalyzed Condition AUNA NNR INFORMATION ONLY NWF [iv)(A) Specified System Actuation AESF NONR NI DESCRIPTION Include: Systems affected, actuations and their initiating signals, causes, effect of event on plant, actions taken or planned, etc. (Continueon back) 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 (XSW1 DB).

Appendix R analyses performed by Gilbert/Commonwealth (now WorleyParsons) 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 XSWI DB. 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 trainsitioning 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 No. 46811). Corrective actions have been taken to address this issue.

NOTIFICATIONS YES NO WILL BE ANYTHING UNUSUAL OR NRC RESIDENT L -0 ....... NOT UNDERSTOOD? []YES (Explain above) NO STATE(s) _ _ DID ALL SYSTEMS []YES Li NO (Explain above)

LOCAL V( FUNCTION AS REQUIRED?

OTHER GOV AGENCIES _ _ MODE OF OPERATION ESTIMATED ADDrT1ONAL INFO ON BACK MEDIA/PRESS RELEASE UNTIL I CORRECTED: RESTART DATE: [] YES ] NO NRC FORM 361 (12-2000)