As reported by a U.S. Nuclear Regulatory Commission (NRC) media release, Exelon Nuclear's Byron Unit 2 atomic reactor near Rockford, IL, primary electrical grid power was lost and safety and cooling systems had to run from emergency backup diesel generators when smoke was seen coming from a switchyard transformer. However, when the plant's fire brigade responded, they could not find the fire. The NRC activated its incident response center in Region III headquarters in Lisle, IL to monitor the situation.
As revealed by Exelon's "Event Report," offsite firefighters were called in, Unit 1 is still at full power, and Unit 2's cool down "steam [is] leaving via atmospheric relief valves."
An initial AP report on the incident stated: "The steam contains low levels of tritium, a radioactive form of hydrogen, but federal and plant officials insisted the levels were safe for workers and the public...[NRC] officials also said the release of tritium was expected...[NRC spokeswoman Viktoria] Mitlyng said officials can't yet calculate how much tritium is being released. They know the amounts are small because monitors around the plant aren't showing 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...Tritium is relatively short-lived and penetrates the body weakly through the air compared to other radioactive contaminants."
But the linear no threshold theory, endorsed by the U.S. National Academies of Science for decades, holds that any exposure to radioactvity, no matter how small, still carries a health risk, and such risks are cumulative over a lifetime. It would be more honest for NRC officials to states that the tritium releases from Byron are "acceptably risky," in their judgment, but not "safe." After all, tritium is a potent radionuclide, a clinincally proven cause of cancer, mutations, and birth defects, and if inhaled, ingested, or absorbed through the skin, can integrate anywhere in the human body, right down to the DNA level.
A follow up article by AP quoted NRC spokeswoman Viktoria Mytling as assuring that the reactor would not be re-started until a root cause of the incident was determined, and the problem fixed. However, such a promise by NRC at Davis-Besse, near Toledo, was recently broken by NRC: widespread cracking in the reactor's concrete shield building, a secondary radiological containment structure, did not stop NRC from rubberstamping the reactor's re-start on December 6th, even though the root cause, extent, and fix for the cracking have still not been determined.
The most recent update from AP reports that Exelon has announced a cause for the incident: a failed electrical insulator, which fell off.