ENS 41377
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ENS Event | |
|---|---|
02:46 Feb 6, 2005 | |
| Title | 4160 Volt Relaying and Metering Single Failure Vulnerability |
| Event Description | This report is being made pursuant to 10CFR50.72(b)(3)(ii)(B). At 20:46 on 02/05/05 while reviewing Operation Experience from another Nuclear Site, it was discovered that the design of the AC Auxiliary Power System incorporates a common circuit which could result in a bus lockout preventing the re-energization of both unit one safeguards buses from either onsite or offsite power sources due to a single failure in the common portion of the circuitry. This common circuit includes various metering circuits and is also connected to overcurrent devices that feed breaker lockout relays. Should a failure occur on these common circuits, all breakers supplying power to these buses would be opened, locked out, and prevented from reclosure onto the buses.
Due to the loss of the ability to accommodate a single failure, one offsite power source ( CT11 ) has been declared inoperable and Technical Specification 3.8.1 Condition A, entered. Corrective actions are in progress to isolate the common circuit and eliminate the single point vulnerability. The licensee notified the NRC Resident Inspector. See similar events #41362 (Crystal River), #41366 (LaSalle), #41369 (Quad Cities) ,#41370 (Dresden) and #41377 (Monticello).
The event reported on February 6, 2005 (4160 volt relaying and metering single failure vulnerability, NRC Event Number 41377) is hereby retracted. Subsequent analysis has concluded that a common mode failure resulting in a simultaneous lockout of both safeguards 4160 volt Bus 15 and Bus 16 due to the common metering circuit was not a credible event in the as-found condition. The analysis showed that the required magnitude of a fire induced fault is much greater than the available fault current in any of the associated circuits. The analysis also showed that dual bus lockout due to an open circuit under non-fire induced conditions is not credible since the imbalance current will be less than the trip setpoint of the affected relays. Thus, although the plant had been in an unanalyzed condition, that condition has now been shown to have not significantly degraded plant safety and is, therefore, not reportable under the requirements of 10 CFR 50.72(b)(3)(ii)(B). Additionally, NMC will be submitting a letter to cancel the associated LER 1-05-01. The licensee notified the NRC Resident Inspector. Notified R3DO (Louden). |
| Where | |
|---|---|
Prairie Island  Minnesota (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+-2.05 h-0.0854 days <br />-0.0122 weeks <br />-0.00281 months <br />) | |
| Opened: | Warner Andrews 00:43 Feb 6, 2005 |
| NRC Officer: | John Mackinnon |
| Last Updated: | Jun 13, 2006 |
| 41377 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (88 %) |
| After | Power Operation (88 %) |
WEEKMONTHYEARENS 526382017-03-20T21:39:00020 March 2017 21:39:00
[Table view]10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Historical Event Related to Past Operability ENS 518772016-04-21T20:50:00021 April 2016 20:50:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Missing Fire Barriers ENS 516422016-01-08T01:00:0008 January 2016 01:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition - Appendix R Credited Procedures Not in Place ENS 516162015-12-21T22:25:00021 December 2015 22:25:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Non-Compliant Fire Protection Manual Operator Actions ENS 514982015-10-26T12:03:00026 October 2015 12:03:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Associated with a High Energy Line Break ENS 509942015-04-19T22:45:00019 April 2015 22:45:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Non Compliance with 10 Cfr 50 App R ENS 508012015-02-10T08:50:00010 February 2015 08:50:00 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Voids Identified That Result in an Unanalyzed Condition ENS 505312014-10-13T19:25:00013 October 2014 19:25:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to a Missing Fire Barrier ENS 505232014-10-10T22:17:00010 October 2014 22:17:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Missing Fire Barrier ENS 504752014-09-19T18:53:00019 September 2014 18:53:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Missing Fire Barriers ENS 503622014-08-08T15:26:0008 August 2014 15:26:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Lack of Appropriate Fuse Protection ENS 496852013-12-31T15:33:00031 December 2013 15:33:00 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Removal of Multiple Steam Generator Lateral Support Shims and Bumpers ENS 493612013-09-19T17:20:00019 September 2013 17:20:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition No Documented Plan in Place to Receive Additional Fuel Oil During Maximum Probable Flood Condition ENS 491282013-06-17T21:15:00017 June 2013 21:15:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Potential Unanalyzed Condition - Carbon Dioxide Fire Suppression System Does Not Meet Design Requirements ENS 479492012-05-22T21:30:00022 May 2012 21:30:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Identified During a Fire Protection Review ENS 475222011-12-09T17:59:0009 December 2011 17:59:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition- Degraded Fire Barrier Between Fire Areas ENS 466992011-03-25T15:53:00025 March 2011 15:53:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Potential Unanalyzed Condition Due to Power Level Greater than Limit ENS 465082010-10-23T00:49:00023 October 2010 00:49:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition - Battery Chargers May Lockup During a Design Basis Event ENS 463182010-10-07T18:52:0007 October 2010 18:52:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Degraded Fire Barrier ENS 462612010-09-16T18:43:00016 September 2010 18:43:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition - Degraded Fire Barrier Identified ENS 458552010-04-19T03:25:00019 April 2010 03:25:00 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Lco 3.0.3 Entry and Loss of Safety Function Due to Loss of Turbine Building High Energy Line Break Compensatory Measure ENS 455672009-12-14T18:00:00014 December 2009 18:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Related to Certain Fire Conditions ENS 449312009-03-23T22:00:00023 March 2009 22:00:00 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition for Postulated Missile Hazard That Could Disable Both Trains of Component Cooling ENS 447732009-01-14T17:30:00014 January 2009 17:30:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Manual Actions for Fire Not in Compliance ENS 443792008-07-31T18:45:00031 July 2008 18:45:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Postulated High-Energy Line Break That Could Disable Both Trains of Component Cooling ENS 435922007-08-24T16:30:00024 August 2007 16:30:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Fire Barrier Separation Criteria Not Met for Afwp Rooms ENS 434042007-06-04T21:00:0004 June 2007 21:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Identified Non Compliant Fire Protection Manual Operator Actions ENS 430102006-11-25T01:45:00025 November 2006 01:45:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition ENS 413772005-02-06T02:46:0006 February 2005 02:46:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 4160 Volt Relaying and Metering Single Failure Vulnerability 2017-03-20T21:39:00 | |
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