Radioactive cesium fallout on Tokyo from Fukushima concentrated in glass microparticles

June 26, 2016

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 ~4.4x1011 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 localised 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".
NOTE: the headline of this press release was shortened to comply with Eurekalert restrictions. The original was "Most radioactive caesium fallout on Tokyo from Fukushima accident was concentrated in glass microparticles"

Goldschmidt Conference

Related Radioactivity Articles from Brightsurf:

Attacking tumors directly on identification
The combination of a biomolecule and a metal complex can target, bind, mark and damage cancer cells.

Can oilfield water safely be reused for irrigation in California?
Reusing low-saline oilfield water mixed with surface water to irrigate farms in the Cawelo Water District of California does not pose major health risks, as some opponents of the practice have feared, a study led by Duke University and RTI International researchers finds.

Cold War nuke tests changed rainfall
Historic records from weather stations show that rainfall patterns in Scotland were affected by charge in the atmosphere released by radiation from nuclear bomb tests carried out in the 1950s and '60s.

New procedure for obtaining a cheap ultra-hard material that is resistant to radioactivity
The material has been made using the technique of laser zone floating, which consists of fusion by means of the application of intense laser radiation and then rapid solidification.

Distribution of highly radioactive microparticles in Fukushima revealed
New method allows scientists to create a quantitative map of radioactive cesium-rich microparticle distribution in soils collected around the damaged Fukushima Daiichi Nuclear Power Plant Nuclear Power Plant (FDNPP).

Are doctors treating more thyroid cancer patients than necessary?
New research may help change treatment practices for patients diagnosed with low risk thyroid cancer.

New model suggests lost continents for early Earth
A new radioactivity model of Earth's ancient rocks calls into question current models for the formation of Earth's continental crust, suggesting continents may have risen out of the sea much earlier than previously thought but were destroyed, leaving little trace.

How slick water and black shale in fracking combine to produce radioactive waste
Study explains how radioactive radium transfers to wastewater in the widely-used method to extract oil and gas.

First reliable estimates of highly radioactive cesium-rich microparticles released by Fukushima disaster
Scientists have for the first time been able to estimate the amount of radioactive cesium-rich microparticles released by the disaster at the Fukushima power plant in 2011.

Artificial intelligence accurately predicts distribution of radioactive fallout
Researchers at the University of Tokyo Institute of Industrial Science created a machine-learning-based tool that can predict where radioactive emissions from nuclear power plants will disperse.

Read More: Radioactivity News and Radioactivity Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to