Fukushima nuclear fallout spread through oceans, researchers say

The dispersal model is ASR's Pol3DD.
The model is forced by hydrodynamic data from the HYCOM/NCODA system which provides on a weekly basis, daily oceanic current in the world ocean.
The resolution in this part of the Pacific Ocean is around 8km x 8km cells.
We are treating only the sea surface currents.
Particles in the model are continuously released near the Fukushima Daiichi power plant since March 11th.
The dispersal model keeps a trace of their visits in the model cells.
The results here are expressed in number of visit per surface area of material which has been in contact at least once with the highly concentrated radioactive water.

From HeraldSun

MOST of the radioactive fallout from the disaster at the Fukushima nuclear plant dropped into the ocean and began circling the planet, Japanese researchers say.

Up to 80 per cent of the caesium released by the Fukushima Daiichi power plant after the March 11 disaster landed in the Pacific and made its way into other oceans around the world, scientists at the Meteorological Research Institute said.

"The rest has fallen on land" in and around Fukushima, said Hiroshi Takahashi, a researcher at the institute in Ibaraki, northeast of Tokyo.

"The results mean the ocean was more contaminated than land, although recent data have shown that ocean pollution resulting from the accident was well below levels affecting humans," Takahashi said.

Researchers said the radioactive materials, including caesium-137, an isotope with a half-life of more than 30 years, were widely dispersed when they entered the oceans and each particle would measure less than one micrometre - one seventh the size of a human red blood cell.

Using computer simulations, they calculated the material was first blown northeast over eastern Russia and Alaska, before falling into the Pacific and reaching the western coast of mainland US around March 17, Takahashi said.

The materials were believed to have completed their first around-the-globe trip by March 24, he said, adding that the results would be presented to an academic meeting in Nagoya, central Japan.

Several previous studies, including one produced in France last month, have concluded the fallout had been hugely diluted by ocean currents and, except for near-shore species, posed no discernible threat.

Japan has been on alert for the impact of radiation since an earthquake and resulting tsunami struck the northeast of the country on March 11, crippling the Fukushima Daiichi nuclear power plant.

Its cooling systems were knocked offline and reactors were sent into meltdown, resulting in the leaking of radiation into the air, oceans and food chain.

Links :

• ASR : Floating tsunami debris tracking system
• JapanToday : Fukushima radioactive fallout mostly dropped into sea: study