Excelon, the plant operator, hopes to replace the insulator by Tuesday evening.
From Chicago Tribune quoting AP (1/31/2012)
Exelon: Failed insulator caused outage at Byron nuclear plant
Exelon Energy officials say they've traced a power failure at a nuclear reactor in northern Illinois to an electrical insulator in a switchyard.
The insulator failed and fell off Monday morning, causing one of the reactors at the Byron Generating Station to shut down automatically, company spokesman Paul Dempsey says.
The bad insulator will be sent to a lab for analysis and officials hope to replace it by Tuesday evening. It's unclear how soon before the reactor could return to service.
Steam containing low levels of tritium, a radioactive form of hydrogen, is being vented to reduce pressure within the reactor. But federal and plant officials say the levels are safe for workers and the public. The plant is 95 miles northwest of Chicago.
The switchyard is similar to a large substation that delivers power to the plant from the electrical grid and from the plant to the electrical grid.
Diesel generators were supplying the reactor with electricity, though it hasn't been generating power during the investigation into what happened. One question is why smoke was seen from an onsite station transformer, though no evidence of a fire was found when the plant's fire brigade responded, U.S. Nuclear Regulatory Commission spokeswoman Viktoria Mitlyng said.
She said Exelon was testing equipment and inspecting various systems to determine exactly what went wrong, and no repairs would be made until the root cause was found.
"If you do a Band-Aid fix and have the same situation, it's not in anybody's interest to have a repeat," Mitlyng said, adding that the NRC is monitoring the activities.
Oh really? No kidding. I thought what nuclear power operators do is Band-Aid fixes. Just look at TEPCO.
The article continues with the mention of tritium. They don't know how much tritium has been released into the environment, but they know it's small because the radiation levels haven't changed around the plant. Uh huh.
Full article at the link.
The commission declared the incident an "unusual event," the lowest of four levels of emergency. Commission officials also said the release of tritium was expected.
Mitlyng said officials can't yet calculate how much tritium was 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 steam that was being released was coming from the turbine side.