Part 1 of 2 Parts
On March 11, 2011, an earthquake off the Japanese coast caused a tidal wave that led to flooding of a nuclear power plant on the coast of the Fukushima Prefect. Three of the reactors melted down and one of those exploded which destroyed a fourth reactor. A huge plume of dirt, debris, and smoke containing radioactive materials was spewed into the air above the site and spread over that part of Japan. What was not known until 2013 was that the material in the radioactive plume released by the explosions also contained glass beads the size of bacteria that contained high levels of radioactive cesium.
These radioactive beads have been found in soil and air samples all over the zone contaminated by the disaster. The beads are of special concern because they contain much higher levels of radioactive cesium than the other particles in the radioactive plume. Because they are tiny, they are easily inhaled deep into the lungs. Because they have a glass shell, they tend not to dissolve in body fluids. This means that they could continue to damage body tissues for a long time if inhaled.
In addition to posing a major health threat, these particles are also of scientific interest because a close examination of them can shed light on exactly what happened when the reactors exploded. This may be of use in deciding exactly how to proceed with the clean up of the Fukushima site.
Following the accident, it was first thought that all of the radioactive cesium released in the disaster would be a form that could dissolve in water so it would be distributed pretty evenly throughout the environment contaminated by the disaster. When the scientists examined the contamination, they found radioactive hotspots that contained high levels of cesium as well as bits of iron and zinc. These hotspots were enclosed in a shell of silica or glass. Within a few miles of the nuclear power plant, the beads also contained tiny pieces of uranium dioxide nuclear fuel from the reactor cores.
The cesium beads were produced early in the meltdown following the flooding. The reactor cooling systems were damaged by the tsunami which resulted in the fuel heating up. As the temperature rose, the metal cladding covering the fuel rods began to break down and release hydrogen gas. Apparently, a spark triggered an explosion in the accumulating hydrogen gas. The glass beads contain a physical record of the sequence of chemical reactions that took place as a result of the disaster. This helps scientists form a timeline of damage and may help them devise a better strategy for cleaning up the damaged reactors.
The composition of the beads indicates that cesium and other fission products were vaporized during the meltdown of the cores and ultimate condensed like rain drops. The condensing clusters of fission products attracted bits of iron dioxide and zinc dioxide that had been created by the corrosion and disintegration of the cladding on the fuel rods. Some of the silica in the concrete of the plant buildings vaporized into silicon dioxide which condensed around the clusters of fission products, iron and zinc.
Please read Part 2