IAEA experts at the Fukushima Daiichi nuclear power plant

Fukushima radiation contamination worse than initially thought

Scientists using a new method of detecting radioactive particles have warned that there was a significant release during the Fukushima nuclear accident that could pose a risk to humans.

The method allows scientists to quickly count the number of caesium-rich micro-particles in Fukushima soils and quantify the amount of radioactivity associated with these particles.

The research, which was carried out by scientists from Kyushu University, Japan, and the University of Manchester, contradicts initial findings in the immediate aftermath of the 2011 Fukushima meltdown.

It was thought that only volatile, gaseous radionuclides, such as caesium and iodine, were released from the damaged reactors. However, it has become apparent that small radioactive particles, termed caesium-rich micro-particles, were also released.

Scientists have shown that these particles are mainly made of glass and that they contain significant amounts of radioactive caesium as well as smaller amounts of other radioisotopes, such as uranium and technetium.

The abundance of these micro-particles in Japanese soils and sediments, and their environmental impact, is poorly understood. But the particles are very small and do not dissolve easily, meaning they could pose long-term health risks to humans if inhaled.

Therefore, scientists need to understand how many of the micro-particles are present in Fukushima soils and how much of the soil radioactivity can be attributed to the particles. Until recently, these measurements have proven challenging.

The new method makes use of a technique called autoradiography, which uses an imaging plate placed over contaminated soil samples covered with a plastic wrap. The radioactive decay from the soil is recorded on the plate as an image, which is then read onto a computer.

The scientists say radioactive decay from the caesium-rich micro particles can be differentiated from other forms of caesium contamination in the soil.

The scientists tested the new method on rice-paddy soil samples retrieved from different locations within the Fukushima prefecture. The samples were taken close to and far away from the damaged nuclear reactors at 4km and 40km. The new method found caesium-rich micro-particles in all of the samples and showed that the amount of caesium associated with the micro-particles in the soil was much larger than expected.

Dr Satoshi Utsunomiya, associate professor at Kyushu University, Japan, and the lead author of the study, said: “When we first started to find caesium-rich micro-particles in Fukushima soil samples, we thought they would turn out to be relatively rare. Now, using this method, we find there are lots of caesium-rich microparticles in exclusion zone soils and also in the soils collected from outside of the exclusion zone.

“We hope that our method will allow scientists to quickly measure the abundance of caesium-rich micro-particles at other locations and estimate the amount of caesium radioactivity associated with the particles. This information can then inform cost-effective, safe management and clean-up of soils contaminated by the nuclear accident.”

In March a Greenpeace survey found that even seven years after the catastrophic disaster, the people, towns and villages in the surrounding area are still being exposed to excessive levels of radiation. 

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