A detailed aerial survey of radioactive contamination within a 160-kilometer radius of the Fukushima No. 1 nuclear plant shows that some districts close to the nuclear plant were relatively unaffected while others many kilometers away have become radiation hot-spots.
A detailed aerial survey of radioactive contamination within a 160-kilometer radius of the Fukushima No. 1 nuclear plant shows that some districts close to the nuclear plant were relatively unaffected while others many kilometers away have become radiation hot-spots.
The education ministry survey of cesium-134 and cesium-137 contamination as of July 16 shows, for instance, that Fukushima city, more than 60 km from the disaster, had more contamination than some areas only a few kilometers directly north of the plant.
Parts of western Tochigi prefecture, far to the south of the plant, were recording between 30 kilobecquerels and 59 kilobecquerels of radioactivity per square meter, while some areas within 100 km were below that figure.
According to an Atomic Energy Society of Japan panel, radioactive contamination from the Fukushima plant was largely governed by local weather conditions immediately following the disaster.
A panel at the Atomic Energy Society of Japan concluded that much of the contamination in surrounding areas was the result of rain and snow falls immediately after the hydrogen explosion at the plant's No. 2 reactor on March 15.
More rain and snow between March 20 and 23, with the wind again blowing toward land, worsened the situation.
"If what happened at the No. 2 reactor on March 15 had happened a couple of days earlier or later, damage would have been significantly less," said Hiromi Yamazawa, professor of environment and radiation at Nagoya University and a member of the panel.
The researchers combined information on the flow of radioactivity from the plant with weather data from the Japan Meteorological Agency.
The radioactive plume from the reactor began moving toward land on March 15, blowing toward the Kanto plain until noon that day. In the afternoon, most of the plume was over Fukushima Prefecture. Rain and snow that evening deposited it on the prefecture.
Radioactive material released from the plant on March 20 fell to the ground in rain and snow in northern parts of Miyagi Prefecture and southern parts of Iwate Prefecture between late March 20 and early March 21.
Meanwhile, the plume turned back toward land on March 20, moving across the Kanto region from east to west and turning southward. On March 21 and 22 fallout reached the coastal areas of Ibaraki Prefecture and Chiba Prefecture, with rainfall across the Kanto region increasing the contamination.
Details of the Atomic Energy Society of Japan panel's findings will be published on the society's website.
The Japanese Society of Soil Science and Plant Nutrition is calling for immediate removal of surface soil at highly contaminated locations.
Many nuclear experts agree that the most effective way of reducing nuclear pollution in school grounds and on farmlands is to remove surface soil, but that raises the thorny issue of where the polluted soil should be stored.
Currently, the only viable option is to bury contaminated soil dug up at schoolyards on the same premises. Cesium-137 has a half-life of about 30 years.
Radioactive contamination from the Fukushima plant was made worse by weather conditions immediately following the hydrogen explosion at the plant's No. 2 reactor on March 15, according to researchers.
A panel at the Atomic Energy Society of Japan concluded that much of the contamination in surrounding areas was the result of rain and snow on the same day as the blast. The wind was blowing toward land at the time, ensuring that significant amounts of radioactive material were deposited on settled areas.