ENS 46844
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ENS Event | |
|---|---|
12:24 Mar 20, 2011 | |
| Title | "a" Train Reactor Protection System Unexpectedly De-Energized Resulting in a Half Scram Signal |
| Event Description | On March 20, 2011, at approximately 7:24 a.m. CDT, the 'A' reactor protection system (RPS) bus was unexpectedly de-energized. Plant systems responded as designed, resulting in a half-scram signal and the actuation of the Division 1 primary containment isolation sub-system. The Division 1 primary containment isolation valves closed in several balance-of-plant systems. After confirming that no valid RPS trip signal had occurred, operators executed the appropriate procedures to return the affected systems to the proper configuration, and to reset the half-scram signal. Plant capacity was not affected by this event.
This event is being reported in accordance with 10CFR50.73(a)(1) as an automatic actuation of the Division 1 primary containment isolation valves in multiple systems resulting from an invalid signal. Each of the two redundant distribution buses in the RPS system is normally powered by its own motor-generator (MG) set. The investigation of this event determined that the output breaker of the 'A' MG set had tripped open. The most likely cause for this trip was a malfunction of the over-voltage relay circuit card in the MG set. Although the troubleshooting was inconclusive, there apparently was a momentary transient in the output of the trip setpoint adjustment potentiometer on the card, likely caused by oxidation on the contacting surface between the wiper arm and the windings. The over-voltage relay card on the 'A' MG set was replaced, and the unit was restored to service. Preventative maintenance tasks are being revised to periodically cycle all potentiometers in the MG set control circuits to wipe oxidation from the windings. The Licensee has notified the NRC Resident Inspector. |
| Where | |
|---|---|
River Bend  Louisiana (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation | |
| Time - Person (Reporting Time:+1271.08 h52.962 days <br />7.566 weeks <br />1.741 months <br />) | |
| Opened: | Danny Williamson 11:29 May 12, 2011 |
| NRC Officer: | John Shoemaker |
| Last Updated: | May 12, 2011 |
| 46844 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 572062024-05-14T00:28:00014 May 2024 00:28:00
[Table view]10 CFR 50.73(a)(1), Submit an LER Invalid Partial Containment Isolation ENS 541212019-04-30T11:50:00030 April 2019 11:50:00 10 CFR 50.73(a)(1), Submit an LER 60-Day Optional Telephonic Notification Due to Invalid Actuation of a General Containment Isolation Signal ENS 517842016-01-10T08:43:00010 January 2016 08:43:00 10 CFR 50.73(a)(1), Submit an LER Invalid Actuation of the Primary Containment Isolation Logic ENS 510032015-02-24T22:02:00024 February 2015 22:02:00 10 CFR 50.73(a)(1), Submit an LER 60-Day Optional Telephone Notification of Invalid System Actuation Due to Motor Generator Output Breaker Trip ENS 507742014-12-06T16:12:0006 December 2014 16:12:00 10 CFR 50.73(a)(1), Submit an LER 60 Day Optional Report - Half Scram and a Division 2 Primary Containment Isolation Signal ENS 468442011-03-20T12:24:00020 March 2011 12:24:00 10 CFR 50.73(a)(1), Submit an LER "a" Train Reactor Protection System Unexpectedly De-Energized Resulting in a Half Scram Signal ENS 445172008-08-01T00:30:0001 August 2008 00:30:00 10 CFR 50.73(a)(1), Submit an LER Invalid Actuation of Containment Isolation Valves Due to a Power Failure ENS 443472008-06-02T11:24:0002 June 2008 11:24:00 10 CFR 50.73(a)(1), Submit an LER Invalid System Actuation of Division 1 Containment Isolation Valves ENS 442782008-04-23T20:56:00023 April 2008 20:56:00 10 CFR 50.73(a)(1), Submit an LER 60-Day Optional Notification of Invalid Specified System Actuation ENS 430122006-09-29T18:33:00029 September 2006 18:33:00 10 CFR 50.73(a)(1), Submit an LER Invalid Specific System Actuation ENS 408472004-05-22T09:29:00022 May 2004 09:29:00 10 CFR 50.73(a)(1), Submit an LER Invalid Actuation of Division 1 Primary Containment Isolation Due to Loss of a Rps Bus 2024-05-14T00:28:00 | |
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