Wind and Rain Steer Radiation’s Reach

[jpak]

http://www.nytimes.com/2011/03/16/world/asia/16worst.html

Experts say it is impossible to forecast how events at Japan’s stricken nuclear plant will unfold, whether there will be a meltdown or other crisis at one or more of the reactors that results in a large release of radioactivity into the environment. And even if such a release occurred, the impact in Japan and elsewhere would depend greatly on wind and rain and how long the release lasted.

“We’re in uncharted territory here,” said Robert Alvarez, a nuclear expert and adviser to the secretary of energy during the Clinton administration. “But in very general terms, the worst-case scenario would be a catastrophic release of radiation that will not necessarily happen all at once.”
That would make the event similar to, and perhaps worse than, the Chernobyl accident in 1986, in which large amounts of radioactivity were released and hundreds of square miles of land in Ukraine were left uninhabitable. But without such a catastrophic release, the events would likely be closer in scale to the partial meltdown in 1979 at Three Mile Island in Pennsylvania, where the plant’s containment structure held and a relatively small amount of radioactivity was released.

So far, the problems at the Fukushima Daiichi plant in Japan are more severe than at Three Mile Island but less so than in Chernobyl.
The Chernobyl reactor, which caught fire after electrical tests resulted in a series of explosions, was not surrounded by a containment structure, as the Japanese reactors are. So a key factor in Japan is whether, if one or more of the reactors has a full meltdown of its nuclear fuel, the containment barriers hold. Complicating matters is the presence of large amounts of spent fuel — which contain most of the same radioactive elements as the fuel in the reactor — in storage ponds that are outside any containment barrier.

Experts differ as to whether breaching of the containment is likely or not. “There’s quite a lot of redundancy and barriers built into the system,” said Mary Lou Dunzik-Gougar, an assistant professor of nuclear engineering at Idaho State University. “A full-fledged meltdown might result in a breach of the pressure vessel, with the fuel dropping into the lower part of the plant. But it’s not going to go very far.”

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