More than half of Fukushima fallout ended up in sea: study

Kyodo

More than half of the radioactive materials that were emitted into the atmosphere in the days after the Fukushima nuclear disaster started have since fallen into the ocean, according to a recent simulation by a team of researchers.

Between 70 and 80 percent of the radioactive cesium from the Fukushima No. 1 power plant in Fukushima Prefecture had fallen into the sea by April, with the rest having fallen on land, according to the simulation done by the Meteorological Research Institute in Tsukuba, Ibaraki Prefecture, and other researchers.

“The Fukushima nuclear power plant is located on the eastern edge of Japan, so only small amounts ended up falling on land because (such materials) get carried by the westerlies between March and April,” said Yasumichi Tanaka, a senior researcher at the Meteorological Agency institute and part of the research team. However, it suggests the fallout that did not make landfall polluted the sea, he added.

A simulation model applied in the study was developed by the institute and the agency, and was used to see how such radioactive isotopes as cesium-131, cesium-134 and cesium-137 got dispersed in the days after March 11.

On the premise that the materials dispersed with each particle smaller than 1 micrometer, the simulation showed they largely completed a trip around the globe in roughly 10 days after first crossing the Pacific.

The materials spread mostly northbound and reached the western coast of the U.S. mainland around March 17 after passing through eastern Russia and Alaska, according to the simulation. They are likely to have largely completed a round-the-Earth trip around March 24.

Most of the radioactive materials fell with rain as they got carried through the atmosphere, the study showed, saying that about 65 percent of the cesium-131 released into the air in the disaster has since fallen into the sea.