Scientists find new kind of Fukushima fallout — Forbes

” Some of the radioactive material that escaped the Fukushima Daiichi nuclear reactor in 2011 took a form no one was looking for, scientists have discovered. Now they have to figure out what it means for Japan and for future disasters.

Radioactive cesium—specifically, cesium-137—is one of the waste products of nuclear power. It’s also one of the most dangerous substances in a nuclear disaster like Chernobyl or Fukushima.

One reason why is that the type of radiation it emits is particularly damaging to our bodies. Another is that cesium-137 dissolves in water. That means it can spread quickly through the environment and get into the plants, animal and water we consume.

Until now, scientists and disaster experts thought cesium-137 fallout from the Fukushima reactor meltdown was in this soluble form. That guided their cleanup efforts, like removing and washing topsoil, and helped them map where radiation might spread.

It turns out that wasn’t entirely true. Satoshi Utsunomiya, a geochemist at Kyushu University in Japan, announced over the weekend that he had found cesium-137 in a new form: trapped inside tiny glass particles that spewed from the damaged reactors. These particles are not water soluble, meaning we know very little about how they behave in the environment—or in our bodies. He found the particles in air filters placed around Tokyo at the time of the disaster.

According to Utsunomiya, high temperatures inside the malfunctioning reactors at the Fukushima plant melted and broke down the concrete and metal in the buildings. Silica, zinc, iron, oxygen and cesium-137 fused into millimeter-wide glass microparticles, each about the size of a pin’s head. Lifted into the atmosphere by the fires raging at the plant, they then blew about 240 kilometers southwest to Tokyo.

“As much as 89% of all of the cesium [in Tokyo] was in fact in these particles. It’s profound,” says Daniel Kaplan, a geochemist at Savannah River National Laboratory in South Carolina. He attended Utsunomiya’s lecture describing the findings at the ongoing Goldschmidt Conference in Yokohama, Japan.

Kaplan says similar particles were observed near the Chernobyl reactors after the explosion there in 1986. But they were only seen within about 30 kilometers; beyond that, cesium-137 was only observed in rain.

Japanese researchers had previously found smaller versions of these cesium-containing glassy particles in Tsukuba, about 170 km from Fukushima, although apparently not at such high concentrations. One earlier paper also suggested that cesium-137 might work its way out of the particles over time.

The discovery could change how we model fallout from nuclear disasters. Kaplan explains that it might add a new variable to the models we use to predict where radioactive particles will go and how long they’ll stay there. It might also change how we treat cesium-137 during cleanup and monitoring.

It is probably still too early to say what this means for people living in Tokyo or elsewhere in Japan. Kaplan thinks the amount of radiation they received probably hasn’t changed. Whether they got it from water-soluble cesium-137 or from these particles, the radiation dose was the same—and for Tokyo residents, that number was within the margin of safe exposure.

The bad thing about water-soluble cesium-137 is that it can easily get into our bodies from soil by way of plants and animals. This new discovery alleviates that concern. But it opens up a new possibility we know little about.

“If the particles are in the air—because that’s how they get to Tokyo—then when you are aspirating this air you should find them in some ways on your lungs,” says Bernd Grambow, who studies nuclear waste chemistry as head of the SUBATECH laboratory in France.

Water-soluble cesium-137 that makes it into our lungs passes into the bloodstream and is peed out within a few weeks. But Grambow says we really don’t know what happens to insoluble cesium-137-containing particles if they get in our lungs. Some of them are likely coughed out or removed by our lungs’ other normal processes. As for the rest, Grambow says we don’t know how long they might remain.

He cautions that any internal radiation from particles containing cesium-137 would be much less than the doses people got from external radiation, which would come from cesium-137 and other radioactive elements in the soil or the environment around them. “We don’t know very much, and my point is only that they should be studied,” Grambow says.

Utsunomiya’s next step is finding out how much of the cesium-137 that ended up in soils in Tokyo and elsewhere was in these glass particles. That way, researchers will be able to better understand how cesium made its way out of the reactor and into the environment. “
by Sam Lemonick

Most radioactive caesium fallout on Tokyo from Fukushima accident was concentrated in glass microparticles — EurekAlert!; Simply Info

” New research shows that most of the radioactive fallout which landed on downtown Tokyo a few days after the Fukushima accident was concentrated and deposited in non-soluble glass microparticles, as a type of ‘glassy soot’. This meant that most of the radioactive material was not dissolved in rain and running water, and probably stayed in the environment until removed by direct washing or physical removal. The particles also concentrated the radioactive caesium (Cs), meaning that in some cases dose effects of the fallout are still unclear. These results are announced at the Goldschmidt geochemistry conference in Yokohama, Japan.

The flooding of the Fukushima Daiichi Nuclear Power Plant (FDNPP) after the disastrous earthquake on March 11 2011 caused the release of significant amounts of radioactive material, including caesium (Cs) isotopes 134Cs (half-life, 2 years) and 137Cs (half-life, 30 years).

Japanese geochemists, headed by Dr Satoshi Utsunomiya (Kyushu University, Japan), analysed samples collected from within an area up to 230 km from the FDNPP. As caesium is water-soluble, it had been anticipated that most of the radioactive fallout would have been flushed from the environment by rainwater. However, analysis with state-of-the-art electron microscopy in conjunction with autoradiography techniques showed that most of the radioactive caesium in fact fell to the ground enclosed in glassy microparticles, formed at the time of the reactor meltdown.

The analysis shows that these particles mainly consist of Fe-Zn-oxides nanoparticles, which, along with the caesium were embedded in Si oxide glass that formed during the molten core-concrete interaction inside the primary containment vessel in the Fukushima reactor units 1 and/or 3. Because of the high Cs content in the microparticles, the radioactivity per unit mass was as high as ~4.4×1011 Bq/g, which is between 107 and 108 times higher than the background Cs radioactivity per unit mass of the typical soils in Fukushima.

Closer microparticle structural and geochemical analysis also revealed what happened during the accident at FDNPP. Radioactive Cs was released and formed airborne Cs nanoparticles. Nuclear fuel, at temperatures of above 2200 K (about as hot as a blowtorch), melted the reactor pressure vessel resulting in failure of the vessel. The airborne Cs nanoparticles were condensed along with the Fe-Zn nanoparticles and the gas from the molten concrete, to form the SiO2 glass nanoparticles, which were then dispersed.

Analysis from several air filters collected in Tokyo on 15 March 2011 showed that 89% of the total radioactivity was present as a result of these caesium-rich microparticles, rather than the soluble Cs, as had originally been supposed.

According to Dr Satoshi Utsunomiya;

“This work changes some of our assumptions about the Fukushima fallout. It looks like the clean-up procedure, which consisted of washing and removal of top soils, was the correct thing to do. However, the concentration of radioactive caesium in microparticles means that, at an extremely localized and focused level, the radioactive fallout may have been more (or less) concentrated than anticipated. This may mean that our ideas of the health implications should be modified”.

Commenting, Prof. Bernd Grambow, Director of SUBATECH laboratory, Nantes, France and leader of the research group on interfacial reaction field chemistry of the ASRC/JAEA, Tokai, Japan, said:

“The leading edge observations by nano-science facilities presented here are extremely important. They may change our understanding of the mechanism of long range atmospheric mass transfer of radioactive caesium from the reactor accident at Fukushima to Tokyo, but they may also change the way we assess inhalation doses from the caesium microparticles inhaled by humans. Indeed, biological half- lives of insoluble caesium particles might be much larger than that of soluble caesium”. ”

Goldschmidt Geochemistry Conference

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Read a similar article by SimplyInfo that sheds more light on the radioactive fallout from Fukushima Daiichi.