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Nine Mile 2 nuclear reactor in Oswego County shut down this morning after two recirculation pumps shut off during a maintenance operation.

(John Berry | The Post-Standard)

SCRIBA, N.Y. -- Operators at Nine Mile Point Unit 2 nuclear reactor shut down the plant this morning after pumps that circulate water through the reactor shut off while being shifted to a lower speed.

Unit 2, which produces up to 1,360 megawatts, shut down at 9:04 a.m. Constellation Energy Nuclear Group, which operates the plant, did not predict when it would return to operation. The adjacent 620-megawatt Unit 1 reactor was not affected and remains at 100 percent power, said Jill Lyon, speaking for CENG, a unit of Exelon Corp.

Nine Mile 2 had been operating at about 78 percent power since Nov. 26 as crews made repairs to the feedwater heating system, Lyon said. Today, as part of that work, operators reduced power further to facilitate the repairs.

As operators powered the unit down, they shifted the recirculation pumps to a lower speed. During the shift, both pumps shut down, which according to procedure requires an immediate manual shutdown of the reactor, Lyon said.

The pumps were subsequently restarted and are operating, but plant officials are still investigating what caused them to fail and what repairs are needed, Lyon said. Once repairs to the equipment are complete, the unit will begin a return to service, she said.