“You aren’t going to have any radiological material that, by the time that it traveled those large distances, could present any risk to the American public,” said Mr. Carney.
Still, radiation emitted by the stricken Fukushima Daiichi nuclear plant has been detected by US Navy ships 100 miles northeast of ground zero. Tokyo, to the south, has seen an increase in radiation levels. How can US officials be so certain that San Francisco won’t feel the after effects if things get worse?
The answer to that question may be time, and distance. It would take days for prevailing winds to blow radioactive material from Japan to the US. Over that period, with that far to travel, rain and wind would disperse the radioactivity, according to the NRC.
Using an atmospheric modeling tool developed by the National Oceanic and Atmospheric Administration, weather expert Jeff Masters has attempted to predict where any potential radioactive plume from the Fukushima Daiichi plant might go. The vast majority of times he runs the data, the plume stays over water for five to seven days prior to landfall. On his blog, “Weather Underground,” he writes that such a long time spent over the ocean means that the vast majority of radioactive particles would settle naturally or be washed out of the sky by precipitation.