Illinois nuclear reactor loses power, venting steam

A nuclear reactor at a northern Illinois plant in USA shut down onMonday after losing power, and steam was being vented to reduce pressure,according to officials from Exelon Nuclear and federal regulators.

Unit 2 at Byron Generating Station, about 95 miles northwest of Chicago, shutdown at 10:18 a.m., after losing power, Exelon officials said. Dieselgenerators began supplying power to the plant, and operators began releasingsteam to cool the reactor from the part of the plant where turbines areproducing electricity, not from within the nuclear reactor itself, officialssaid.

The steam contains low levels of tritium, a radioactive form of hydrogen, butfederal and plant officials insisted the levels were safe for workers and thepublic.

The U.S. Nuclear Regulatory Commission declared the incident an "unusualevent," the lowest of four levels of emergency. Commission officials alsosaid the release of tritium was expected.

Exelon Nuclear officials believe a failed piece of equipment at a switchyardcaused the shutdown. The switchyard is similar to a large substation thatdelivers power to the plant from the electrical grid and that takes power fromthe plant to the electrical grid. Officials were still investigating theequipment failure.

Nuclear Regulatory Commission spokeswoman Viktoria Mitlyng said officials can'tyet calculate how much tritium is being released. They know the amounts oftritium are small because monitors around the plant aren't showing increasedlevels of radiation, she said.

Tritium molecules are so small that tiny amounts are able to pass fromradioactive steam from the reactor into the water used to cool the turbines andother equipment outside the reactor. The steam that was being released wascoming from the turbine side.


The amount of releasing steam helps "take away some of that energy stillbeing produced by nuclear reaction but that doesn't have anywhere to gonow." Even though the turbine is not turning to produce electricity, shesaid, "you still need to cool the equipment."

Tritium is relatively short-lived and penetrates the body weakly through theair compared to other radioactive contaminants.

Candace Humphrey, Ogle County's emergency management coordinator, said countyofficials were notified of the incident as soon as it happened and that publicsafety was never in danger.

"It was standard procedure that they would notify county officials,"she said. "There is always concern. But, it never crossed my mind thatthere was any danger to the people of Ogle County."

Unit 1 was operating normally while engineers investigate why Unit 2 lostpower, which comes into the plant from the outside power grid, Mitlyng said.Smoke was seen from an onsite station transformer, she said, but no evidence ofa fire was found when the plant's fire brigade responded.

Mitlyng said Nuclear Regulatory Commission inspectors were in the control roomat Byron and in constant contact with the agency's incident response centre inLisle, Ill.

In March 2008, federal officials said they were investigating a problem withelectrical transformers at the plant after outside power to a unit wasinterrupted.

In an unrelated issue last April, the commission said it was conducting specialinspections of backup water pumps at the Byron and Braidwood generatingstations after the agency's inspectors raised concerns about whether the pumpswould be able to cool the reactors if the normal system wasn't working. Theplants' operator, Exelon Corp., initially said the pumps would work but laterconcluded they wouldn't.