ML11182A917
| 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 Operations Center 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\ V C 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)
OIER U PECFE RECUT. (see last column) (ii)(B) Unanalyzed Condition AUNA NNR INFORMATION ONLY NWF [iv)(A) Specified System Actuation AESF NI NONR DESCRIPTION Include: Systems affected, actuations and their initiating signals, causes, effect of event on plant, actions taken or planned, etc. (Continue on 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 I UNTIL CORRECTED:
RESTART DATE: [] YES ] NO NRC FORM 361 (12-2000)