The trace amount of radioactive tritium released in steam to cool a reactor during a shutdown at an Illinois nuclear plant was not enough to present a danger to the public, according to the first estimates by the U.S. Nuclear Regulatory Commission.
Preliminary calculations indicate that the radiation dose from Monday's release at the Byron Generating Station was less than 0.001 (one one-thousandth) percent of the commission's annual dose limit of 100 millirems. That amount is thought to be safe to workers and the public, agency spokeswoman Viktoria Mitlyng said.
"That is a very, very, very small amount," Mitlyng said, much less than the dose from a dental X-ray (0.5 millirem) or a smoke detector (0.008 millirem). Exposure to radiation increases a person's lifetime risk of cancer, so minimizing exposure is a good idea.
Final data on the tritium release will be available to the public after the commission conducts a special investigation into how some equipment responded to the outage, Mitlyng said.
Exelon Energy was still working Thursday to get the reactor back online at the facility about 95 miles northwest of Chicago, said spokesman Paul Dempsey.
Monday's outage started when an electrical insulator, a piece of protective equipment that helps regulate the flow of electricity in the plant's switchyard, failed and fell off the metal structure to which it was attached. That interrupted power and caused the reactor to automatically shut down as a precaution.
Tritium, a radioactive form of hydrogen, is relatively short-lived and penetrates the body weakly through the air compared to other radioactive contaminants.
The amount released Monday was estimated to be less than escaped in a 2010 steam release at the Braidwood nuclear plant about 50 miles southwest of Chicago, Mitlyng said.