Radioactivity detected 60 miles from the Fukushima Daiichi nuclear plant

Pentagon officials reported Sunday that helicopters flying 60 miles from the Fukushima Daiichi nuclear plant picked up small amounts of radioactive particulates — still being analyzed, but presumed to include cesium-137 and iodine-121 — suggesting widening environmental contamination.

The detection of the highly radioactive elements heralds the beginning of an ecological and human tragedy. The two radioactive isotopes can mean only one thing: One or more of the reactor cores is badly damaged and at least partially melted down.

Japanese reactor operators now have little choice but to periodically release radioactive steam until the radioactive elements in the fuel of the stricken reactors stop generating intense heat, a process that can continue for a year or more even after fission has stopped.

In the best case, operators will pump enough seawater and other coolants to squelch overheating. Such a success would prevent further releases of radiation beyond the unknown amount spewed into the air by controlled venting and the explosion of a reactor containment building.

In such a scenario, the only casualties would probably be the handful of plant workers reported Sunday to be suffering from acute radiation sickness.

If the last-ditch efforts to cool the reactors fail, the heavy cylindrical cores — each containing tons of radioactive fuel — could flare to hotter than 4,000 degrees and melt through the layers of steel and cement engineered to contain them.

Such a meltdown may be under way, said Arnie Gundersen, chief engineer at the consulting firm Fairewinds Associates. Gundersen helps oversee the Vermont Yankee nuclear plant, whose reactors are the same vintage and design as those of the stricken Japanese reactor.

If a full meltdown occurs, a huge molten lump of radioactive material would burn through all containment, destroy the building and fall to the ground, exposed. A toxic stew of exotic radioactive particles would then spread on the wind and rain.

On Sunday, the International Atomic Energy Agency said the prevailing winds at Daiichi are blowing to the northeast, out to sea, and should continue to do so for the next three days.

Such emissions would not endanger the United States, the Nuclear Regulatory Commission announced Sunday. Given the thousands of miles between the countries, the danger could simply dissipate over the Pacific.

It's impossible to know how a plume of radioactivity traveling over the ocean might affect sea life, said Edwin Lyman, a senior scientist at the Union of Concerned Scientists, which strongly opposes nuclear power. Lyman said that simulations he has run on possible nuclear disasters in the U.S. estimate "tens of thousands of cancer deaths" from a total meltdown.

A 2005 census counted 103 million people on Honshu, including the population of Tokyo, which lies 150 miles to the southwest of Fukushima Daiichi.

Lyman's simulations, which rely on NRC computer code, show unfavorable winds could spread radioactivity far beyond the 12.5-mile evacuation zone, much like Chernobyl in 1986.

In that disaster, a reactor exploded and a fire raged for 10 days, sending radioactive particles hundreds of miles. There is some scientific consensus that at least 6,000 to 7,000 excess cases of thyroid cancer have occurred in the 25 years since.

The increased thyroid cancer was the result of the kind of broad food-chain contamination that can arise from a nuclear incident. Cows ate grass exposed to iodine-131 and then produced radioactively hazardous milk that was unknowingly fed to children, who are most at risk.