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Particles from Fukushima meltdown contained plutonium

fukushima-nuclear-disaster-plutonium_1600Local residents who live around the 20km exclusion zone around the Fukushima Dai-Ichi Nuclear Power Plant undergo a screening test for possible radiation at screening center on September 13, 2011 in Minamisoma, Fukushima Prefecture, Japan.

 

August 6th, 2020 Posted by Stanford

Microscopic particles emitted during the Fukushima nuclear disaster contained plutonium, according to a new study.

The microscopic radioactive particles formed inside the Fukushima reactors when the melting nuclear fuel interacted with the reactor’s structural concrete.

Nearly ten years after meltdown at the Fukushima Daiichi Nuclear Power Plant caused a nuclear disaster, the new information about the extent and severity of the meltdown and the distribution patterns of the plutonium have broad implications for understanding the mobility of plutonium during a nuclear accident.

“The study used an extraordinary array of analytical techniques in order to complete the description of the particles at the atomic-scale,” says coauthor Rod Ewing, co-director of the Center for International Security and Cooperation (CISAC) at Stanford University.

The researchers found that, due to loss of containment in the reactors, the particles were released into the atmosphere and many were then deposited many miles from the reactor sites.

Studies have shown that the cesium-rich microparticles, or CsMPs, are highly radioactive and primarily composed of glass (with silica from concrete) and radio-cesium (a volatile fission product formed in the reactors). But the environmental impact and their distribution is still an active subject of research and debate. The new work offers a much-needed insight into the Fukushima Daiichi Nuclear Power Plant (FDNPP) meltdowns.

The study used an extraordinary array of analytical techniques in order to complete the description of the particles at the atomic-scale.

The researchers used a combination of advanced analytical techniques, including synchrotron-based micro-X-ray analysis, secondary ion mass spectrometry, and high-resolution transmission electron microscopy, to find and characterize the plutonium that was present in the CsMP samples. They initially discovered incredibly small uranium-dioxide inclusions, of less than 10 nanometers in diameter, inside the CsMPs; this indicated possible inclusion of nuclear fuel inside the particles.

Detailed analysis revealed, for the first-time, that plutonium-oxide concentrates were associated with the uranium, and that the isotopic composition of the uranium and plutonium matched that calculated for the FDNPP irradiated fuel inventory.

“These results strongly suggest that the nano-scale heterogeneity that is common in normal nuclear fuels is still present in the fuel debris that remains inside the site’s damaged reactors,” says geochemist Satoshi Utsunomiya of Kyushu University, who led the team.

“This is important information as it tells us about the extent [and] severity of the meltdown. Further, this is important information for the eventual decommissioning of the damaged reactors and the long-term management of their wastes.”

With regards to environmental impact, Utsunomiya says, “as we already know that the CsMPs were distributed over a wide region in Japan, small amounts of plutonium were likely dispersed in the same way.”

This is important information for the eventual decommissioning of the damaged reactors and the long-term management of their wastes.

The team “will continue to experiment with the CsMPs, in an effort to better understand their long-term behavior and environmental impact,” says Gareth T. W. Law, a coauthor on the paper from the University of Helsinki. It is now clear that CsMPs are an important vector of radioactive contamination from nuclear accidents.”

“While the plutonium released from the damaged reactors is low compared to that of cesium; the investigation provides crucial information for studying the associated health impact,” says coauthor Bernd Grambow of Nantes/France.

Utsunomiya emphasizes that this is a great achievement of international collaboration. “It’s been almost ten years since the nuclear disaster at Fukushima,” he says, “but research on Fukushima’s environmental impact and its decommissioning are a long way from being over.”

The paper appears in Science of the Total Environment.

Additional researchers from Kyushu University, University of Tsukuba, Tokyo Institute of Technology, National Institute of Polar Research, University of Helsinki, Paul Scherrer Institute, Diamond Light Source, and SUBATECH (IMT Atlantique, CNRS, University of Nantes) contributed to the work.

Source: Stanford University via Kyushu University

Original Study DOI: 10.1016/j.scitotenv.2020.140539

https://www.futurity.org/fukushima-nuclear-disaster-plutonium-2417332-2/

 

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August 7, 2020 Posted by | Fukushima 2020 | , , | 1 Comment

Radioactive cesium fallout on Tokyo from Fukushima concentrated in glass microparticles

Public Release: 26-Jun-2016 Goldschmidt Conference

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 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”.

http://www.eurekalert.org/pub_releases/2016-06/gc-rcf062316.php

June 27, 2016 Posted by | Fukushima 2016 | , , , | Leave a comment

Radioactive “Glassy Soot” Fell Over Tokyo After the Fukushima Meltdown

It’s science no one wishes was necessary.

Most of the radioactive material that rained down on Tokyo following the meltdown at the Fukushima Daiichi Nuclear Power Plant was encapsulated in glassy microparticles, researchers have found.

The findings, which will be presented on Monday at the Goldschmidt conference in Japan, show that the radioactive fallout from the 2011 earthquake and subsequent nuclear disaster has been poorly understood. Previously, it was assumed that most of the radiation that fell dissolved in rain. This would mean that it would wash out of the soil and through the environment with the hydrologic cycle.

However, what actually happened is that, in the midst of the meltdown, molecules of radioactive caesium and nanoparticles of iron-zinc oxides became embedded in silicon oxide glass. This occurred because of the interaction between the molten core and the concrete containment units.

These tiny glass particles entered the air and fell as soot on the surrounding region. Because the radioactive molecules are contained in an insoluble medium, they will not wash out of the soil with rainwater to the same extent.

“It looks like the clean-up procedure, which consisted of washing and removal of top soils, was the correct thing to do,” says Dr. Satoshi Utsunomiya, who will present the findings on Monday. “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.”

Beyond the consequences for the environment, there are significant consequences for human health. Breathing caesium encased in glass particles may have a very different impact from exposure to it as radioactive rain, and it may be dangerous at a much higher or lower concentration. The half-life of the material may also depend heavily on the medium.

This information will be valuable in assessing the ongoing impacts the Fukushima disaster. Hopefully, no nuclear meltdown on that scale occurs again, but if one does, this new science will help governments better respond to the crisis.

https://www.inverse.com/article/17503-radioactive-glassy-soot-fell-over-tokyo-after-the-fukushima-meltdown

June 27, 2016 Posted by | Fukushima 2016 | , , , , | Leave a comment