This telephone report is being made in accordance with
10 CFR 50.73(a)(2)(iv)(A) as an event or condition caused by an invalid signal that resulted in an automatic actuation on November 19, 2006 at 2028
CST of the following
Primary Containment Isolation System (
PCIS) groups:
The systems above functioned as designed. Reactor Protection System (RPS) bus 'B' had lost power from its Motor Generator (MG) and was found de-energized which caused the actuations. Power was restored to the RPS bus 'B' from auxiliary power, and plant systems were recovered.
In addition to the actuations reported above, the following actuations also occurred and functioned as designed.
- RPS half-scram on B channel (no rods moved);
- Half-group isolations of the following PCIS Groups;
- Group 3, Reactor Water Clean-up (one valve shut),
- Group 7, Recirculation Loop Sample Lines (valves were already shut),
The cause of the invalid signal was 'B' RPS MG set high voltage condition produced by a faulty voltage adjust potentiometer in the voltage regulator. This caused a protective relay to trip the RPS MG exciter field which caused the subsequent low voltage and loss of the 'B' RPS bus.
The licensee notified the NRC Resident Inspector.
