Researchers are planning to create a detailed map showing levels of radioactive contamination around the Fukushima No. 1 nuclear power plant.
About 300 experts from Osaka University, Hiroshima University, the University of Tokyo and other academic and research institutions will start collecting soil samples in May at up to 10,000 locations in 1,500 designated areas, mainly in Fukushima Prefecture, to create a soil-pollution map.
The map will be designed primarily to help designate evacuation areas.
The science ministry intends to use the map as a picture of the situation concerning radioactive pollution in areas around the crippled plant
The project was formed on the initiative of three scientists: Mamoru Fujiwara, associate professor, Osaka University Research Center for Nuclear Physics; Masaharu Hoshi, professor, Hiroshima University Research Institute for Nuclear Medicine and Biology; and Takaharu Otsuka, professor, University of Tokyo Center for Nuclear Study.
In response to a call by the researchers, experts nationwide in nuclear physics, environmental radioactivity and meteorology have offered to help.
The group will also receive support from a Russian research institute of radiation medicine, which carried out environmental surveys in areas contaminated by the 1986 Chernobyl accident.
Around mid-May, the team will start its work by dividing the area around the stricken nuclear power plant spanning 100 kilometers north-south and 60 kilometers east-west into 1,500 2-kilometer square zones. The researchers will collect soil samples at five to seven points in each zone to measure levels of such radioactive isotopes as iodine-131, cesium-137 and strontium-90. The level of radiation in each zone will be shown on the pollution map.
The group also plans to conduct a radiation survey in the 20-kilometer off-limits zone around the plant, and is holding talks with the government for the survey.
Levels of soil pollution are affected by such factors as topographical and meteorological conditions. Measurements at two points in the same area can differ widely.
Detailed pollution data are essential for careful planning of evacuation zones.
The group plans to carry out the survey every few months to update the map.
Regular updates are important because, compared with the areas around the Chernobyl plant, those around the Fukushima plant are more undulating and rainy, according to the researchers. Rain causes soil drainage and significant changes in radiation levels over time.
The group will also study the effects of soil contamination on human health by using data from health checkups of local residents.
It was three years after the Chernobyl accident that a detailed map of cesium-137 contamination was completed.
Since the measurements of iodine-131, which has a short half life of about eight days, in areas around the Chernobyl plant were not sufficient, it was impossible to make an accurate assessment of the effects of this radioactive material on the health of local residents, in particular the correlation between levels of iodine-131 contamination and the incidence of thyroid cancer. Exposure to iodine-131, which is concentrated in the thyroid when absorbed by the body, is believed to increase the risk of thyroid cancer.
The science ministry is also developing its own soil pollution map, but it is currently measuring radiation levels at only 53 locations.
“We hope to work with the researchers and make effective use of the map,” said an official at the ministry.
“An early radiation survey is indispensable for accurately estimating the risk of developing cancer due to exposure to radioactive materials,” said Osaka University’s Fujiwara. “Basic data about soil pollution will also help develop convincing evacuation plans for local residents.”