Almost ten years after the disaster at the Fukushima Daiichi Nuclear Power Plant, researchers discovered a new kind of highly radioactive mineral particles in the fallout.
The plant suffered major damage from the magnitude 9.0 earthquake and tsunami that hit Japan on March 11, 2011. The wave disabled the emergency generators required to cool the reactors, causing a partial meltdown in one of the six reactor cores that eventually led to explosions, which released large amounts of radioactive material into the air. Fallout contaminated the surrounding area with high levels of radioactive uranium, strontium, lithium, sulfur and zirconium. Airborne small (micrometer-sized) particles were widely distributed, reaching as far as Tokyo.
Analyzing soil samples of the contaminated area, researchers at the University of Kyushu discovered 300-micrometer large particles. The particles are composed of amorphous silica, with traces of radioactive cesium and carbon in a glassy matrix. The surface of the particles is covered by fragments of a lead-tin alloy, aluminum-silicate minerals, quartz and limestone.
The researchers think that the mineral particles formed during the meltdown and explosion in the reactor core. The high temperatures partially vaporized the containment vessel. Droplets of glass condensed from the air-gas mix, incorporating fragments of metal and concrete. The chemical traces and radioactive elements in the glass matrix reflect the chemical composition of the nuclear fuel during the last moments of the core meltdown.
Owing to their large size, the health effects of the particles are likely limited to direct contact and very localized. After the disaster, the Japanese authorities declared a 20 km (12 miles) evacuation zone around the nuclear plant a no-go area. Despite being highly radioactive, the particles are too heavy to be dispersed by water and wind outside the evacuation zone.
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