FirstEnergy's Beaver Valley Unit One nuclear reactor in Shippingport was shut down Monday afternoon because of a problem with the main unit transformer.
The company and the Nuclear Regulatory Commission said the unplanned, non-emergency shutdown of the 911-megawatt nuclear reactor occurred at 4:59 p.m.
The transformer converts power generated by the plant to voltage for use in the region's electric distribution system. Its relay tripped, a function designed to protect the transformer during a malfunction.
Neil Sheehan, an NRC spokesman, termed the reactor shutdown "uneventful."
"All safety systems operated as expected and the plant was shut down safely," FirstEnergy spokeswoman Jennifer Young said in an email. "There were no impacts on the health and safety of plant workers or the public as a result of the issue. Beaver Valley Unit 1 is currently stable at zero percent reactor power."
It is unknown whether the cold weather caused or contributed to the problem, Ms. Young said, but the company does not expect "any direct impact on customers." She said Beaver Valley Unit Two, a sister nuclear generator to Unit One, and the Bruce Mansfield coal-fired power plant, both also in Shippingport, are fully operational.
"It's too early to tell what caused the problem," Ms. Young said. "There are many potential reasons this could happen, and the cold weather is one of them."
The shutdown triggered the automatic activation of a fire-suppression system that doused the transformer with water, which immediately froze, according to the NRC.
Mr. Sheehan, in an NRC release, said power plant personnel either will have to find a way to melt that ice or wait for temperatures to climb above freezing to conduct an inspection of the transformer.
Ms. Young said the Unit One reactor will remain shut down until the problem is identified and fixed. If FirstEnergy needs to replace the transformer, she said, the company has a backup on site that could be installed.
PJM Interconnection, the electricity grid operator for more than 61 million people in Pennsylvania and 12 other states plus the District of Columbia, said the Unit One shutdown adds to power-supply concerns during high usage caused by the frigid weather. On Tuesday morning, PJM asked the public to conserve electricity.
"When [electricity] demand is high, the loss of any generation is a concern, and Beaver Valley is a big unit and a big loss.
But it's just one of many thousands of megawatt losses affecting the system," said PJM spokesman Ray Dotter. "It has an effect. It makes the power supply tighter, but there are also a number of peaking units running that increase generation.
"So it's fair to say [Beaver Valley's shutdown] has an impact. But it's not fair to say it's the reason for any supply problems we may experience."
Don Hopey: email@example.com or 412-263-1983. First Published January 7, 2014 12:34 PM