But, even in the hypothetical scenario of a Chernobyl-like event in Japan, it is highly unlikely there would be any health-related consequences in the US, both Thrall and Hall said.
Thrall pointed out that the US tested nuclear and hydrogen bombs in the Pacific Ocean for years, and dropped atomic bombs in Japan during World War II, "which released, in the aggregate, far more radiation than these [Japanese] power plants would ever come close to releasing, and it all dissipated in the atmosphere, at least from the standpoint of any health implications in the US."
According to Thrall, the average background radiation exposure in the US at sea level is 3.2 mSv.
Both Thrall and Hall said that any radiation release that would bring that up to about 6 mSv would be cause for alarm and would trigger actions to mitigate the health effects, including the use of potassium iodide tablets to address iodine-131 exposure and ferric hexacyanoferrate(II) (Radiogardase) capsules to mitigate cesium-137 exposure.
But both called that scenario highly unlikely.
Kirby Kemper, PhD, a physicist at Florida State University, told MedPage Today and ABC News in an e-mail that the health risk attributable to low levels of radiation remains controversial.
But, he noted by way of comparison, "people in Denver ... have about twice the background radiation level compared to people in Florida due to cosmic rays, but actually have a longer life span than people from Florida."
Jerrold Bushberg, MD, a radiation oncologist at the University of California Davis, said that even if there is a risk from radiation drifting over from Japan, it will be trivial relative to the overall risk of cancer.
In an e-mail to MedPage Today and ABC News, Bushberg said that an extra dose of radiation of 40 times the normal background radiation from cosmic rays and geologic sources still would be barely detectable.
"The increased cancer risk from that exposure would be less than 1%," he said.
US Nuclear Plants Should Be Safe
According to the NRC — the US government's atomic energy watchdog — nuclear plants must be designed to withstand "the most severe natural phenomena historically reported for the site and surrounding area. The NRC then adds a margin for error to account for the historical data's limited accuracy."
However, earthquake resistance specifications for two plants on California's coast are lower than some historic quakes in the state, and much less than the magnitude-9.0 temblor that struck Japan last week.