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A small leak of radioactive coolant in a pipe weld discovered Wednesday is now undergoing repair at the Davis-Besse nuclear reactor near Toledo, OH.

Engineers found the leak while they were preparing to resume operations after more than a month-long reactor shutdown for refueling and plant maintenance.

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The leak of radioactive coolant inside the reactor containment building is about one-tenth gallon per minute, said plant owner FirstEnergy Corp. in a report to the Nuclear Regulatory Commission (NRC).

The leaked coolant flowed into a nearby floor drain where they captured it for later processing, said company spokeswoman Jennifer Young. There were no injuries and no radioactivity escaped into the atmosphere, she said.

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The leak did not occur until they pressurized the cooling system in preparation to restart the reactor, she said. Pressurization began on Tuesday.

The engineers were conducting the “walk-down inspection” while the reactor was in “hot standby” mode, with the cooling system running at normal operating pressures and temperatures.

Through the reactor had not yet been re-started, operators on Tuesday had switched on the four massive reactor coolant pumps, which pressurized the system and heated the coolant to about 300 degrees from sheer friction as the pumps pushed it throughout the nuclear core, said Young.

The company’s report noted the coolant was spraying from a pinhole in the socket weld of a three-quarter inch pipe at a 90 degree elbow between a reactor coolant pump and a safety valve.

When they first found the leak, reactor operators immediately began a shutdown and engineers began repair preparations. The plant reached cold shutdown about 1 p.m. Thursday, said Young. Repairs should wrap up over the weekend.

FirstEnergy shut down the 908-megawatt reactor May 6 for normal refueling, inspections and maintenance. Contractors employing more than 1,000 workers joined Davis-Besse employees to replace 68 of the reactor’s 177 fuel rods.

Contractors also worked on preventative maintenance of major components including emergency diesel generators, valves and pumps — though not the coolant pumps and plumbing where the leak occurred. Crews also worked on the power plant’s cooling tower to improve efficiency.

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