05000458/LER-2007-002

06-29-2007

At 1256 CDT on May 4, 2007, an unplanned manual reactor scram was initiated following the loss of cooling on the No. 2 main transformer. Reactor power at the time of the scram was approximately 67 percent. Following the scram, reactor water level briefly decreased below Level 3 as expected, resulting in the automatic closure of two containment isolation valves in the suppression pool cleanup system. This isolation was confirmed to have occurred as designed. Control of reactor pressure and water level was promptly established. No emergency coolant injection ,system actuation was required.

This event is being reported in accordance with 10CFR50.73(a)(2)(iv)(A) as a condition that resulted in the unplanned manual actuation of the reactor protection system. The loss of cooling to the transformer resulted from an electrical fault in the cooling system control cabinet caused by rainwater intrusion. The cabinet was repaired and sealed, and preventative maintenance procedures are to be enhanced to prevent recurrence. The plant responded to the manual scram as expected, thus this event was of minimal safety significance. .

NRC FORM 366 (6-2004) PRINTED ON RECYCLED PAPER

LER-2007-002, Unplanned Manual Reactor Scram Due to Loss of Cooling on No. 2 Main Transformer
Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. • 05000
Event date:	05-04-2007
Report date:	06-29-2007
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
4582007002R00 - NRC Website
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05000458/LER-2007-002

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