Unscheduled trips shut down two U.S. nuclear power reactors this week. The Fort Calhoun Nuclear Station north of Omaha and the Cook Nuclear Plant's Unit 2 were both shut down due to minor incidents.
Indiana Michigan Power said the Cook Unit 2 shut down after a rupture resulted in the release of non-radioactive steam that caused damage to a wall, but did not result in any injuries.
The unit was taken off line at 12:38 a.m. on Wednesday, July 6 “when an expansion joint bellows on a Moisture Separator Reheater ruptured,” the company said. The joint bellows is approximately 48 inches in diameter. The high-pressure, high-temperature steam that escaped caused damage to an adjacent Turbine Building exterior wall. No one was in the area of the rupture, when it occurred.
It was declared an Unusual Event due to the unanticipated nature of the incident, which was terminated at 2:07 a.m.
An Unusual Event is the least serious emergency plan classification and all appropriate notifications were sent out to local, state and federal officials. At the plant, Cook Unit 1 remained at 100 percent power and even Unit 2 reached 100 percent power each day this week, according to the Nuclear Regulatory Commission's daily status reports.
At Cook Unit 2, an analysis of the incident and repairs were undertaken.
The Omaha Public Power District, owners of the Fort Calhoun power plant announced an automatic shut down on Wednesday due to a turbine trip that occurred at 8:41 a.m.
There was no risk to the public, the OPPD said. Station operators followed “appropriate procedures and handled the situation as they have been trained to do,” according to a news brief. There were no injuries and the plant, which is to be closed down by the end of the year for economic reasons, remains safe, OPPD said.
As of Friday, Cook Unit 1 remained at zero percent power according to the NRC's daily status reports.
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