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| Report date | Site | Event description | |
|---|---|---|---|
| 05000368/LER-2013-002 | 4 April 2013 | Arkansas Nuclear | On February 4, 2013, at 1255 CST, Control Room Emergency Chiller 2VE-1A breaker tripped shortly after the chiller was started. 2VE-1A is one of two control room emergency chillers common to both Arkansas Nuclear One (ANO) Unit-1 and ANO Unit-2. The 2VE-1A breaker (2B-52D5) is a Siemens 480 volt, 100 amp molded case circuit breaker. An Apparent Cause Evaluation determined that the the "C" phase load side wire lug was not properly connected when the breaker was installed on November 15, 2012, resulting in a loose connection between the lug and the breaker stab. The condition was corrected and 2VE-1A was declared operable on February 6, 2013. The apparent causes of the condition were determined to be a human performance error during breaker replacement due to the inadequate use of human performance tools and an inadequate molded case circuit breaker testing procedure which did not provide a step to perform a visual inspection of the wire grip style lug after installation. Initial corrective actions included a human performance error review and a requirement for visual verification of the wire lugs for remaining breaker replacement work orders. The Apparent Cause Evaluation provided firm evidence that the condition existed since the breaker was incorrectly installed on November 15, 2012, resulting in the inoperability of 2VE-1A. The redundant 2VE-1B Chiller was considered inoperable from November 26, 2012 to December 3, 2012, resulting in the potential inoperability of both control room emergency chillers and a condition that could have prevented the fulfillment of a safety function. |