Tiny fragments of plutonium may have been carried more than 200 km by caesium particles released following the meltdown at the Fukushima Daiichi nuclear power plant in Japan in 2011. So says an international group of scientists that has made detailed studies of soil samples at sites close to the damaged reactors. The researchers say the findings shed new light on conditions inside the sealed-off reactors and should aid the plant’s decommissioning.
Caesium is a volatile fission product created in nuclear fuel. During the Fukushima meltdown, it combined with silica gas created when melting fuel and other reactor materials interacted with the concrete below the damaged reactor vessel. The resulting glass particles, known as caesium-rich microparticles (CsMPs), measure a few microns or tens of microns across.
Satoshi Utsunomiya and Eitaro Kurihara at Kyushu University and colleagues in Japan, Europe and the US analysed three such particles obtained from soil samples dug up at two sites within a few kilometres of the Fukushima plant. They used a range of techniques to study the physical and chemical composition of these CsMPs, with the aim of establishing whether they contained any plutonium.
Mapping plutonium spread
To date, plutonium from the accident has been detected as far as 50 km from the damaged reactors. Researchers had previously thought that this plutonium, like the caesium, was released after evaporating from the fuel. But the new analysis instead points to some of it having escaped from the stricken plant in particulate form within fragments of fuel “captured” by the CsMPs.
[…]
Implications for decommissioning
The researchers note that previous studies have shown that plutonium and caesium are distributed differently in the extended area around Fukushima, which suggests that not all CsMPs contain plutonium. However, they say that the fact plutonium is found in some of these particles implies that it could have been transported as far afield as the caesium – up to 230 km from the Fukushima plant.
[…]
Read more.
