Nuke’s Water Pumps Catch NRC’s Eye

Friday, February 3, 2012 @ 12:02 PM gHale

A new electrical insulator replaced the failed equipment blamed for a power loss to a nuclear reactor in northern Illinois, and the Nuclear Regulatory Commission (NRC) began a special inspection into how some equipment responded to the outage, officials said.

Exelon Energy began preparations to re-start the Unit 2 reactor at the Byron Generating Station about 95 miles northwest of Chicago, though it was unclear how soon it could return to service, spokesman Paul Dempsey said.

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The insulator, a piece of protective equipment that helps regulate the flow of electricity in the plant’s switchyard, failed Monday morning and fell off its attached metal structure. That interrupted power and caused the reactor to automatically shut down as a precaution.

It was not immediately clear what caused the insulator to fail, but the part will go to a lab for analysis, Dempsey said.

Meanwhile, the NRC began an inspection of water pumps that help cool the reactor, commission spokeswoman Viktoria Mitlyng said.

Some pumps will switch off after a set period of time after detecting an undervoltage to prevent damage, then must manually restart. But some of those pumps shut down and restarted on their own after Monday’s power outage, she said.

She said there was no danger because the plant has multiple backup pumps, but the NRC wants all pumps to perform properly.

“We are asking if all pumps, whether they have a built-in mechanism or not, functioned property and responded as expected and if there were any unexpected problems with equipment,” Mitlyng said.

During the shut-down, steam released to cool the reactor, but was venting from the part of the plant where turbines produce electricity, not from within the nuclear reactor itself, officials said. The steam contained low levels of tritium, a radioactive form of hydrogen, but federal and plant officials insisted the levels were safe for workers and the public.

Releasing steam helped to “take away some of that energy still being produced by nuclear reaction but that doesn’t have anywhere to go now” that the turbines are shut down, Mitlyng said. Even though the turbine is not producing electricity, she said, “you still need to cool the equipment.”

Diesel generators were supplying the reactor with electricity, though it hasn’t been generating power during the investigation. Another reactor at the plant was operating normally.

The NRC declared the incident an “unusual event,” the lowest of four levels of emergency.

Mitlyng said officials can’t yet calculate how much tritium released. They know the amounts were small because monitors around the plant didn’t show increased levels of radiation, she said.

Tritium molecules are so microscopic that small amounts are able to pass from radioactive steam that originates in the reactor through tubing and into the water used to cool turbines and other equipment outside the reactor, Mitlyng said. The released steam was coming from the turbine side.

Tritium is relatively short-lived and penetrates the body weakly through the air compared to other radioactive contaminants. It can cause cell damage if it enters the body, but the amounts released from the Byron station under normal operating conditions and within the steam that vented now is not a health concern, said David Lochbaum, a nuclear engineer and director of the nuclear safety project for the Union of Concerned Scientists.

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