A non-emergency event shut down one of two reactors at Comanche Peak late last week. The report to the Nuclear Regulatory Commission (NRC) followed another event days earlier.
According to Luminant Generation, a subsidiary of Energy Future Holdings, which operates the local facility, the two issues were in no way related, and safety at the plant was at no point compromised.
Each of the incidents, which occurred Wednesday, Oct. 31, and Friday, Nov. 2, were non-emergency events according to the reports.
Comanche Peak Unit 1 was manually tripped at 1:42 a.m. Friday due to high temperature readings from a cooling pump.
"Friday morning, we completed a safe manual trip on Comanche Peak Unit 1 following high temperature indications on a reactor coolant pump motor bearing," Ashley Barrie, corporate communications manager for Luminant, said Saturday. "We are currently looking into the cause and developing a maintenance plan to resolve the issue. We anticipate returning the unit to service as soon as this work is completed."
The manual shut down procedure reportedly went according to plan, safety systems functioned as designed and the event did not cause either of the unit's emergency diesel generators to start.
But the Oct. 31 incident, one of the generators did start.
"We experienced an equipment malfunction, which mistakenly signaled one of the Comanche Peak Unit 1 emergency diesel generators to start," Barrie said. "The issue, which occurred in a logic and relay panel, resulted in one of the unitís emergency diesel generators starting as designed. At no time was power lost to the unit, nor were there any safety issues at the plant."
She said protocol requires the nuclear power plant to notify NRC anytime an emergency diesel generator is started.
"The malfunctioning components in the logic and relay cabinet were replaced and verified satisfactory through testing," Barrie added.
Unit 1 remained offline Tuesday morning, but Barrie said Unit 2, which was in a planned refueling outage, resynchronized with the grid early Friday morning.
Comanche Peak has an operating capacity of 2,300 MW (Megawatt). The local facility accounted for 24 percent of Luminant's energy production - 78,681 GWH (Gigawatt Hour) - in 2011, according to the company's website, with 74 percent produced by coal and 2 percent natural gas.