Waterford — Millstone Unit 3 automatically shut down at 1:47 a.m. Monday after one of the four pumps that deliver cooling water to the nuclear reactor shut down.    

Plant spokesman Ken Holt said Tuesday that after the pump tripped off the plant began an automatic shutdown.

“The reactor shutdown was safe and uncomplicated,” Holt said. “We’re currently in the process of identifying the reason why the pump shut down, and we won’t restart until the cause is identified and the problem corrected.”  

He said the shutdown was not related to the weekend snowstorm.

Unit 3 is the newer and larger of the two operating reactors at Millstone, generating 3,650 megawatts of power. Unit 2 generates 2,700 megawatts. Millstone Power Station is owned by Dominion Resources.

Nuclear Regulatory Commission spokesman Neil Sheehan said the pump shut down after an electrical breaker connected to it tripped, and that plant personnel are focusing on diagnosing the problem with the breaker.

“NRC resident inspectors assigned to Millstone are following up on the company’s evaluation of the problem,” he said. “One of the inspectors responded to the plant during the shutdown and independently verified the reactor was being safely shut down and that operator actions were appropriate.”

j.benson@theday.com

Twitter: @BensonJudy