Fukushima: Uranium detected in fallout

Soil and water microparticles contain long-lived uranium and zirconium nuclides

Researcher taking samples in the exclusion zone around Fukushima Daiichi © Gareth Law
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Long-lasting fallout: The Fukushima nuclear accident could have released more uranium than expected. In microparticles from the fallout researchers have now detected two different uranium compounds. Because uranium has an extremely long half-life, the radioactive contamination could therefore last longer than previously thought. The detection of uranium particles also indicates that parts of the nuclear fuel were also released during the nuclear disaster.

The nuclear accident at the Japanese nuclear power plant Fukushima Daiichi was one of the heaviest in the history of nuclear energy. The failure of the cooling system resulted in a meltdown, in explosions large amounts of radioactive nuclides were released. To date, the situation in the reactors is only partially under control, it comes in the vicinity of the plant again and again to contamination of the sea, groundwater and soil.

What was really in the fallout?

So far, researchers assumed that most of the Fukushima fallout consisted of lighter, gaseous nuclides. After the nuclear accident radioactive isotopes of the elements xenon, lithium, sulfur, strontium and especially of cesium were detected. However, in 2016, researchers found that much of the radioactive cesium did not enter the environment as a gas, but in the form of glassy microparticles.

These microparticles and their exact composition have now been studied more closely by Asumi Ochiai from Kyushu University and his colleagues. For their study, they collected soil and water samples from the exclusion zone around the Fukushima power plant. The sample locations were located a few kilometers from the reactors.

Microparticles also contain uranium

The result: Contrary to previous assumptions, fallout radioactive microparticles contain not only relatively short-lived nuclides such as cesium. "We also detected nanoparticles of two different uranium compounds in these microparticles, " the researchers report. These are 70 nanometer sized crystals of uranium dioxide and 200 nanometer porous crystals of a mixture of uranium and zirconium oxides. display

The nuclear power plant Fukushima Daiichi on March 14, 2011: Radioactive smoke is rising. Digital Globe

Although it has been suspected that traces of uranium could be in the fallout. But in what form and how much was unknown. "This is the first time that we describe the characteristics of the released fuel nanofragments in the atomic scale, " says Ochiai and his colleagues. Our results document that these micro-rotors are very heterogeneous both in terms of their chemical and physical properties. "

Long-lasting and lung-friendly

The problem here is that radioactive zirconium is just as uranium extremely durable: The half-lives are billions of years, as the researchers explain. However, this could mean that the contamination of the exclusion zone and even more remote areas could last much longer than previously thought. In addition: The microparticles are so small that they can be inhaled easily if they are, for example, stirred up from the ground.

The presence of uranium in the microparticles also proves that Fukushima released not only decay products of the nuclear fuel but also parts of the fuel rods themselves. "The particles are a mixture of molten nuclear fuel and reactor materials, " the researchers report, "They reflect the complex thermal processes that occurred in the nuclear reactor during the meltdown."

Notes on the condition of the reactor cores

"It is now urgent to conduct more detailed investigations into the remains of the nuclear fuel also in the reactors themselves and outside the exclusion zone, " says co-author Gareth Law of the University of Manchester, This information is important not least for the operating company Tepco.

Because they provide further indications as to the condition of the molten reactor cores in the plants. So far it is impossible to obtain direct samples or images from the reactor cores the radiation is too high. (Environmental Science and Technology, 2018; doi: 10.1021 / acs.est.7b06309)

(University of Manchester, 02.03.2018 - NPO)