Local planning authorities--either at the state or local level, depending on the place--determine what protective action is warranted in the event of an accident at a nuclear power plant, including an evacuation as in Pennsylvania during the partial meltdown at Three Mile Island. The evacuation begins with whichever way the wind is blowing. "You don't need to evacuate 360 degrees around the plant right away," Milligan says. "At that time, the wind is only going in one direction."
But that wind direction may be a very bad one from an emergency planning perspective. For example, New York City is within 50 miles of the Indian Point nuclear power complex--and could be downwind. "There is no way to evacuate New York City on that time scale," von Hippel argues.
The recommendation is not always to leave, of course, as seen in the case of Three Mile Island. "Evacuations are a big deal," Milligan says. "You are taking people out of their homes. It's not something you want to do lightly, for reasons other than definitely needing to avoid a dose" of radiation. In some accidents, it is better to take shelter. "If it's a plume or puff release, people shelter in houses with the windows closed until the puff has passed overhead," Milligan says.
In Japan, even in the wake of the deadly earthquake and tsunami that left local infrastructure in ruins, thousands of people were evacuated from the vicinity of the nuclear power plant within 24 hours. As a result, Milligan, at least, does not anticipate any changes to the rules for U.S. nuclear power plants stemming from lessons learned from Fukushima. "The planning zones in place now provide adequate protection for public health and safety," she says. "There is nothing we can see in our look [at Fukushima meltdowns] that would indicate that we would need to expand the plume exposure pathway."
Nevertheless, in the case of Fukushima, the USS Ronald Reagan aircraft carrier sailed into the plume of escaping radioactive noble gases on March 12. More than 100 miles away, sailors on the aircraft carrier found levels high enough to exceed the EPA's guidelines for civilians after roughly 10 hours of exposure. "They went up to 130 miles from the plant, and we were still reading a direct gamma shine of 0.6 millirem per hour," explained the NRC's Stephen Trautman on March 12, according to transcripts. Gamma rays are among the most energetic--and therefore dangerous to health--forms of radiation.
In the end, the question is one of risk. No one has died from radioactive contamination as a result of the Fukushima meltdowns, at least not yet. And it may prove impossible to disentangle any extra cancers due to Fukushima's radiation from those that happen as a result of all the other carcinogenic factors a person is exposed to in the modern world--from diet to smoke.
But it remains unclear how far radioactive emissions might reach in the case of a nuclear meltdown like Fukushima. "At that point it's from there, another 50 miles? Another five miles? Another 10 miles? Do you have a sense?" asked NRC chairman Gregory Jaczko on March 12, as he and his staff analyzed computer modeling of a catastrophic meltdown that indicated those guidelines could be exceeded well beyond 50 miles in a worst case scenario. The response from Martin Virgilio, deputy executive director for Reactor and Preparedness Programs: "No sir, I wouldn't...I don't have a value for that."