At 0535 [PDT] on 5/31/12 during power ascension following a maintenance outage, a loss of power to the
Reactor Protection System (
RPS) 'B' occurred due to the unexpected opening of the circuit breaker (RPS-CB-MG2) for the
RPS 'B' motor generator. The loss of
RPS 'B' resulted in a
half scram signal, closure of
Primary Containment Isolation Valves (
PCIVs) from multiple systems and loss of power to
main steam line radiation monitors (MS-RIS-610B & MS-RIS-610D). No plant parameters or maintenance activities existed which would cause the opening of RPS-CB-MG2; therefore, this is considered to be an invalid actuation of a system listed in
10CFR50.73(a)(2)(iv).
The half scram signal, closure of Primary Containment Isolation Valves (PCIVs) from multiple systems, and loss of power to MS-RIS-B & D were an expected response to the loss of RPS 'B'.
Power ascension was temporarily halted. RPS 'B' was repowered from an alternate power supply. The half scram signal was reset, the containment isolation valves were opened and the affected systems were returned to normal operation. Power ascension was resumed. The circuit breaker (RPS-CB-MG2) was replaced and RPS 'B' was returned to its normal power supply.
Initial investigation efforts have not determined a cause for RPS-CB-MG2 opening. Investigations into the cause of RPS-CB-MG2 opening are continuing.
As indicated in 10CFR50.73(a)(1), in the case of an invalid actuation reported under 10CFR50.73(a)(2)(iv)(A), the licensee may, at its option, provide a telephonic notification to the NRC Operations Center within 60 days of discovery of the event instead of submitting a written LER. This 60-day telephone notification is being made to meet the reporting requirements instead of submitting an LER since the actuation was invalid.
The following additional information is provided as specified in NUREG-1022:
The specific train(s) and system(s) that were actuated: PCIVs in multiple systems
EDR-V-19 Drywell Equipment Drain Inboard Isolation Valve
EDR-V-20 Drywell Equipment Drain Outboard Isolation Valve
FDR-V-3 Drywell Floor Drain Inboard Isolation Valve
FDR-V-4 Drywell Floor Drain Outboard Isolation Valve
RWCU-V-1 Reactor Water Cleanup Suction Inboard Isolation Valve
RWCU-V-4 Reactor Water Cleanup Suction Outboard Isolation Valve
RRC-V-19 Reactor Water Sample Inboard Isolation Valve
RRC-V-20 Reactor Water Sample Outboard Isolation Valve
TIP-V-15 Traversing In-Core Probe Purge Isolation Valve
CRD-V-11 Control Rod Drive Scram Discharge Volume Drain Valve
Whether each train actuation was complete or partial:
All PCIVs actuations for a loss of RPS 'B' were complete
The reactor half scram for a loss of RPS 'B' was a partial activation
Whether or not the system started and functioned successfully:
All PCIVs functioned successfully
The licensee notified the NRC Resident Inspector.
