On November 4, 2003 at 2132 the Unit 2
auxiliary feedwater (
AF) system received an inadvertent engineered safety feature (
ESF) actuation signal while in cold shutdown due to the concurrent de-energization of two 6.9 KV buses, i.e., undervoltage on 2/4
reactor coolant pump (
RCP) buses. Following the shutdown of the last remaining
RCP, the 6.9 KV buses were de-energized earlier than planned in the outage schedule. While the 6.9 KV buses were being de-energized, anticipated
transient without
scram (
ATWS) mitigation system (
AMS) testing was in progress. This test requires that the A and B train
AF pump auxiliary
lube oil pumps remain energized. Normally the 6.9 KV buses are not de-energized until after
AMS testing is complete and the
AF pump auxilary
lube oil pumps de-energized. However, with the
AF pump auxiliary
lube oil pumps still energized, the de-energization of the 6.9 KV buses resulted in an
AF actuation signal. This signal resulted in the unplanned, automatic start of both A and B train
AF pump auxiliary
lube oil pumps and the unplanned, automatic opening of both A and B train
AF pump discharge valves. The root causes for the event were: 1) overconfidence by the outage electrical team coordinator which led to his decision to hang the 6.9 KV bus clearance orders (C/O) ahead of schedule (note that there was no process in place to control advancing the schedule activities) and 2) a procedure did not exist for de- energizing the 6.9 KV buses. The corrective actions to prevent recurrence are to develop a procedure to remove the 6.9 KV buses from service with appropriate precautions and limitations to prevent this event from occurring again, and to develop a process for changing outage schedule activities with proper oversight.
This report is being made in accordance with 10 CFR 50.73(a)(2)(iv)(A).
US. NUCLEAR REGULATORY COMMISSION 1 P AC FORM 366A -0-200t) FACILITY NAME (I) DOCKET (2) LER NUMBER (6) PAGE (3) A. Plant operating Conditions Before The Event:
Unit: 2 � Event Date: November 4, 2003 Event Time: 2132 MODE: 5 � Reactor Power: 0 percent Reactor Coolant System [AB]: Unit 2 was in cold shutdown operations during the 10th refueling outage (i.e., A2R10).
No structures, systems or components were inoperable at the start of the event that contributed to the event.
B. Description of Event:.
There were no additional systems or components inoperable at the beginning of this event that contributed to the severity of the event.
At 1641 on November 4, 2003, AMS testing was in progress. To support the test, the AF [BA] system was set up as follows: the auxiliary lube oil pumps for the 2A and 2B AF pumps were energized (i.e., breakers ON), the breaker for the 2A AF pump was racked to TEST and in the open position with the main control board control switch in normal after trip position. The test verifies the starting of the auxiliary lube oil pumps and the opening of the AF pump discharge valves 2AF004A/B.
Ranging of the C/O for the 6.9 KV buses and the expected response of the reactor protection system were discussed during the shift briefing. Moving the C/O placements on the 6.9 KV buses up in the schedule was not discussed during the briefing. The AMS testing in progress was also discussed during the briefing.
The final running RCP was secured at 1915 on November 4, 2003, earlier than planned in the outage schedule. The operations electrical team coordinator reviewed the outage schedule and saw a window of opportunity to de-energize all four 6.9 KV buses earlier than planned in the outage schedule. Based on past outage practices, when the last RCP was stopped, this action was a trigger for starting 6.9 KV bus outages.
The electrical team coordinator performed a pre-job briefing for hanging the C/Os for 6.9 KV buses 256 and 258. During the pre-job briefing, the reactor protection system response was discussed but the AF system response was not.
The electrical team coordinator was aware of the AMS testing in progress, however was not focused on the potential impact of the ANS testing on the AF system alignment. The AMS test procedure did not account for the incompatibility of the AMS testing and the de-energizing of the 6.9 KV buses.
The 6.9 KV bus C/Os were discussed during the shift briefing earlier and was expected to have minimal impact on the plant since all loads on the 6.9 KV buses were shutdown.
At 2129 on November 4, 2003, the C/O for bus 256 was hung and bus 256 was de- energized. At 2132, while hanging the C/O for bus 258, an actuation signal to the Unit 2 AF system was initiated. The 2A and 28 AF pump auxiliary lube oil pumps auto-started. The 2A and 2B AF pump discharge valves automatically opened. At 2140 on November 4, 2003, power was restored to bus 258 and the AF system was restored to its AMS test lineup.
— US. NUCLEAR REGULATORY COMMISSION FACILITY NAME (11 � DOCKET (2) LER NUMBER (6) PAGE (3) Unit 2 � STN 05000457