The design of the
Auxiliary Feedwater (
AF) system is for the
AF pumps to normally take suction from the condensate storage tank. If the condensate storage tank is not available, the essential
service water system provides the alternate supply. Due to the
AF system suction piping and valve configuration, a voided section of pipe could exist in the portion that isolates the condensate storage tank supply from the essential
service water supply. A preliminary vendor analysis has determined that the void fraction to reach the pump in a dynamic scenario exceeds the acceptance criteria for
AF pump operability. Based on past operation in this configuration, the event is being reported as a
unanalyzed condition that significantly degrades plant safety and a condition that could have prevented the fulfillment of a safety function (i.e., remove residual heat) under
10CFR50.72(b)(3)(ii) and
10CFR50.72(b)(3)(v). Further review of the void model and pump performance characteristics are planned.
In 2011, prior to the completion of this analysis. The void was refilled and verified full for both trains at Byron U1 and U2.
Unit 1 is defueled. This condition affects both 'A' and 'B' trains of auxiliary feedwater for both Unit 1 and Unit 2.
The NRC Resident Inspector has been notified.
