海角大神

Japan鈥檚 nuclear crisis has made many people in the US concerned that radioactive contamination might reach American shores. Potassium iodide 鈥� a compound that if ingested guards against some of the most dire side effects of radiation exposure 鈥� is in short supply in some areas, particularly the West Coast.

Anbex Inc., a Virginia firm that is a leading supplier of potassium iodide, sold out its stockpile of tablets over the weekend. The company鈥檚 notes that new product is not expected until April 18.

But US officials on Tuesday said that they believe the worry driving this demand is an overreaction.

鈥淚 think there鈥檚 essentially no concern in terms of the health effects on American shores,鈥� Secretary of Energy Steven Chu told reporters after testifying before the House Energy and Commerce Committee on his department鈥檚 budget.

At the White House, spokesman Jay Carney made the same point, repeating a statement made earlier by a top Nuclear Regulatory Commission official.

鈥淵ou aren鈥檛 going to have any radiological material that, by the time that it traveled those large distances, could present any risk to the American public,鈥� 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鈥檛 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, 鈥�,鈥� 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.

鈥淚t is highly unlikely that any radiation capable of causing harm to people will be left in the atmosphere after seven days and 2000+ miles of travel distance,鈥� Dr. Masters writes.

The Chernobyl disaster, which involved a release of much more radiation than has been the case so far in Japan, spread significant contamination about 1,000 miles, notes Masters.

Of course Chernobyl, in what is now Ukraine, occurred in the heart of Europe, so that contamination had serious health repercussions for nearby populations.

In his congressional testimony, Secretary Chu said he was up early Tuesday morning looking at atmospheric models produced by his department to see where radiation might travel. He added that the crisis in Japan will eventually help the US strengthen the safety of its own reactors.

The administration 鈥渋s committed to learning from Japan鈥檚 experience,鈥� he said.

Chu and other officials have said that the White House remains committed to the development of a diverse set of energy sources, including nuclear power. No new US reactors have come online since the Three Mile Island accident of 1979.

Pressed as to whether Japan鈥檚 troubles could stall nuclear power鈥檚 resurgence in the US, Chu said 鈥淚 still feel it is probably premature to say anything other than, 鈥榃e will learn from this all forms of energy do present risks.鈥� 鈥�