A startling new government study of worst-case accidents at U.S. nuclear plants finds that today's retrofitted reactors pose virtually no health risk to the public.

The "State-Of-The-Art Reactor Consequence Analyses" report by the U.S. Nuclear Regulatory Commission followed five years of analysis of the Peach Bottom nuclear plant in York County and the Surry Power Station in Virginia.

Both plants were considered representative of the two types of nuclear reactors in the U.S.: boiling water reactors such as Peach Bottom and pressurized water reactors such as Three Mile Island.

The study's findings dramatically downgrade the government's view of the threat of radiation releases, even when there is a runaway accident with a long-term power loss and a core meltdown from an earthquake, fire, tornado, flood or operator error.

"What it tells me is that even if you did have a very severe accident at a nuclear plant, the risk is still very low because the event takes such a long time until there is a release of radioactivity, and even when it is released, it's much lower than previously estimated," said Brian Sheron, director of the NRC's Office of Nuclear Regulatory Research.

This is a significant change from the last accident-risk study done by the NRC in 1982.

According to the new SOARCA study, even in an uncontrollable accident scenario, a release of radiation would happen much later than previously projected and would be a much lower dose, according to the study.

For example, the 1982 study predicted a worst-case accident at Peach Bottom could kill 92 people early on. The SOARCA analysis says there would be zero fatalities on first exposure.

Latent cancers — mostly from evacuated residents returning home prematurely — might be nine in 1 million. That's millions of times lower than the overall cancer risk from all sources.

That's partly because of improved safety equipment, operator training and procedures mandated over the years, especially accident-preparation equipment and strategies added since the terrorist attacks of 9/11, according to the study.

Those added measures include back-up power to the plant and portable diesel-driven pumps.

Also, it was found that a radiation release at Peach Bottom in the most likely severe accident scenario — a long-term loss of power with containment failure — would not happen for 20 hours, much later than previously estimated.

That would be valuable time for plant operators to mitigate the accident with outside assistance and ample time to evacuate people living within 10 miles of the plant.

Moreover, the new analysis maintains that much of the released radioactive material would not float into the air, instead sticking to pipes and interior parts of the building.

The study was nearly complete when the Fukushima nuclear accident occurred in Japan. The SOARCA study said there was limited information available on accident details but that there were "many similarities and differences with some of the Peach Bottom sequences."

One short-term blackout sequence of events at Fukushima helped with the evaluation of Peach Bottom, noted Kathy Gibson, in the NRC's Office of Nuclear Regulatory Research.

The NRC will present the study findings and answer questions from 5 to 9 p.m. on Wednesday, Feb. 22, at the Peach Bottom Inn, 6085 Delta Road, Delta, York County.

acrable@lnpnews.com