Limerick Generating Station
Both reactors at Exelon Corp.'s Limerick Generating Station in Montgomery County, Pa., are seen operating March 16, 2011.
(Chris Post | Express-Times File Photo)
The southeastern Pennsylvania nuclear reactor that unexpectedly shut down Monday night was returned to full power Friday, owner Exelon Corp. announced.
Repairs were made to a valve that closed automatically on one of the
Unit 1 reactor's main steam lines, according to a news release from the company.
, Exelon spokeswoman Dana Melia had said. The Unit 2 reactor at Limerick, in
about 30 miles south of Allentown, was unaffected by Monday's incident.
The incident forced the automatic shutdown of the reactor. It remained in what is known as hot shutdown, with control rods inserted in the reactor core, until Friday when Exelon restarted it.
A restart from hot shutdown can take hours to reach full power, much quicker than the gradual ascent in power required from a cold shutdown, said Neil Sheehan, spokesman for the Nuclear Regulatory Commission.
The valve closure caused reactor pressure to rise beyond a pre-determined point that forced the automatic shutdown, the NRC had said.
"It was an unplanned shutdown or a forced outage," Sheehan said. "It would not qualify as an unusual event or any kind of emergency because it doesn't meet the criteria for that."
If a reactor has more than three unplanned shutdowns, also known as scrams, during 7,000 hours of operation, its NRC performance indicator changes from green to white, prompting additional scrutiny. Limerick's Unit 1 had seen a rolling average of 0.9 scrams during the previous 7,000 hours of operations, Sheehan said.
"This will be added to that," he said. "At this point it still keeps them below that threshold ... . It's obviously something that they're going to need to be cognizant of."
Sheehan noted that NRC inspectors will follow up on the incident.
The outage did not impact electrical service to regional customers, Exelon said. Limerick's twin, 1,200-megawatt reactors produce enough carbon-free electricity to power approximately two million homes.