On Thursday, June 29, 2006, at approximately 20:30 the Engineering Department notified the Plant Management that St. Lucie Unit 2 had exceeded the maximum power level allowed by the facility's Operating License (License Condition 3.A). The overpower condition was determined to be approximately 0.5%. This equates to 13.5 MWth reactor core power above the Rated Thermal Power Limit of 2700 MWth. Preliminary data indicates that the overpower condition could have been present between June 20, 2006 and June 29, 2006. This telephone notification is made in accordance with Renewed Facility Operating License No.
NPF-16, License Condition 3.H. A written follow-up report will be submitted within 14 days.
A Distributed Control System (DCS) software error was responsible for the overpower condition. The DCS calculated a slightly lower feedwater flow value which was used as input into the calorimetric power calculation. The error resulted in a non-conservative indicated power in the control room.
When the feedwater flow calculation error was identified, it was apparent that an overpower condition may have occurred. Therefore, a controlled power reduction to approximately 98% was performed in accordance with plant procedures. St. Lucie Unit 2 will remain at a reduced power level until the software error is corrected. The software error is understood and is in the process of being resolved within the corrective action process. An extent of condition review has determined that St. Lucie Unit 1 does not have the same problem.
The licensee notified the NRC Resident Inspector.
