Control Rod Falls into Core, Reactor Down

Wednesday, August 22, 2012 @ 04:08 PM gHale

After a control rod dropped entirely into the core where fission occurs, Calvert Cliffs nuclear power plant operators shut down one of the plant’s two reactors Aug. 12, Nuclear Regulatory Commission (NRC) officials said.

Control rods, which absorb neutrons created by nuclear fission and sustain a chain reaction, gradually lower into or are withdrawn from the core of the nuclear reactor to regulate the reaction’s pace, said NRC spokesman Neil Sheehan.

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When an unplanned drop occurs, however, the fission process can become imbalanced and “pose challenges” for the plant operator, Sheehan said. Such a malfunction also requires operators to shut the reactor down within six hours, he said.

Calvert Cliff’s operators are still trying to determine why a control rod dropped entirely into the core of the plant’s No. 1 reactor at 12:34 p.m. Sunday, Sheehan said. The company filed a formal notification with the NRC at 2:37 p.m. and advised the NRC it had begun shutting down Unit 1 right away.

“It’s a prudent move in this case,” Sheehan said. “It sounds more ominous than it is.”

Although any such incident poses challenges to plant workers because of the radiation and heat in the reactor’s core, the event has not endangered the public or the operators, and there has been no release of radiation, Sheehan said. The event was classified as a “non emergency” on the formal notification form submitted to the NRC by Calvert Cliffs, according to a copy of the form.

Plant operators are working to find out what happened and eventually bring the plant’s unit back online, Sheehan said. Although there have been other instances in the industry when a control rod dropped unexpectedly into a reactor, such malfunctions are “infrequent,” Sheehan said.

Kory Raftery, spokesman for Constellation Energy Nuclear Group could not predict when Unit 1 would be back in operation, but noted Unit 2 is still running at full power at the plant, which is 70 miles south of Baltimore.

“We’ll get back up to 100 percent and connected to the grid as soon as safely possible,” he said.

It’s the third unplanned shutdown of Unit 1 in the past month; the reactor was taken out of service twice in July to fix a pair of leaks, according to Raftery.

Constellation Energy Nuclear Group owns the plant, located in Lusby, MD. It is a joint venture between Exelon Corp. and EDF. The plant’s two reactors produce 1,700 megawatts, or more enough electricity to power more than 1 million homes.

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