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On March 20, 2011, at approximately 7:24 a … 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.</br>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.</br>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.</br>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.</br>The Licensee has notified the NRC Resident Inspector.e has notified the NRC Resident Inspector. +
12:24:00, 20 March 2011 +
46,844 +
11:29:00, 12 May 2011 +
12:24:00, 20 March 2011 +
On March 20, 2011, at approximately 7:24 a … 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.</br>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.</br>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.</br>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.</br>The Licensee has notified the NRC Resident Inspector.e has notified the NRC Resident Inspector. +
Has query"Has query" is a predefined property that represents meta information (in form of a <a rel="nofollow" class="external text" href="https://www.semantic-mediawiki.org/wiki/Subobject">subobject</a>) about individual queries and is provided by <a rel="nofollow" class="external text" href="https://www.semantic-mediawiki.org/wiki/Help:Special_properties">Semantic MediaWiki</a>.
100 +
00:00:00, 12 May 2011 +
Modification date"Modification date" is a predefined property that corresponds to the date of the last modification of a subject and is provided by <a rel="nofollow" class="external text" href="https://www.semantic-mediawiki.org/wiki/Help:Special_properties">Semantic MediaWiki</a>.
02:07:12, 2 March 2018 +
11:29:00, 12 May 2011 +
true +
false +
52.962 d (1,271.08 hours, 7.566 weeks, 1.741 months) +
12:24:00, 20 March 2011 +
"a" Train Reactor Protection System Unexpectedly De-Energized Resulting in a Half Scram Signal +
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