On May 9, 2011, at 1518 Eastern Daylight Saving Time (EDT),
WBN [Watts Bar Nuclear] started a Safety Injection Pump and began to inject into the
Reactor Coolant System contrary to Technical Specification Limiting Condition for Operation 3.4.12, which requires in part for Mode 5 that a Cold Overpressure Mitigation System (
COMS) shall be OPERABLE with a maximum of one charging pump and no safety injection pump capable of injecting into the
RCS and the
accumulators isolated.
The RCS pressure rise was recognized immediately, and the pump was secured within 27 seconds. The pressure reached a maximum of 328 psig. which is below the relief valve setpoint, so no structure, system, or component pressure limit was exceeded at any time. LCO 3.4.12 Condition A was entered immediately. At 1521, the pump breaker was directed to be racked out, and the breaker was reported racked out and verified by 1600, at which time LCO 3.4.12 was exited.
This event was determined to be reportable as a condition prohibited by Technical Specifications in accordance with 10 CFR 50.73(a) (2)(i)(b). This notification is made in accordance with Watts Bar License condition 2.G.
The NRC Resident Inspector has been notified of this event and event notification.
The licensee is investigating the likelihood of a valve mispositioning.
