Clay Could Improve Spent Nuclear Fuel Storage Sites’ Safety

Nuclear Waste - Not a Game
Nuclear Waste – Not a Game

One might point to nuclear power as a zero-emissions alternative to fossil-fuel-based power generation, but it does have a couple of very special problems, such as nuclear waste disposal and the ever-present danger of nuclear accidents.

We may point to reducing carbon dioxide as the means to curb climate change, which would affect everyone on the planet, but a nuclear accident or poorly-stored nuclear waste can render uninhabitable large areas of the landscape. For example, the area surrounding Pripyat and the Chernobyl Nuclear Power Plant, after the accident in 1986, will not be inhabitable for at least another 20,000 years, thanks to radioactive isotope strontium-90 [28.8-year half-life] and caesium 137 [30.2-year half-life] that saturates the landscape. There are other radioactive isotopes that result from fission of nuclear fuel, such as iodine 131 [8-year half-life] or iodine 129 [15.7-million-year half-life] which makes disaster and waste storage a critical concern.

Nuclear waste in deep geological repositories won’t disappear completely for a couple of billion years, but they can, we hope, be stored well enough to prevent leakage. This is the reason that repositories are located in non-seismically-active areas, far from major human habitation, and the nuclear waste itself is placed in specialized containers.

One key element, in both repositories and the containers themselves, is the presence of clay, which has naturally-low permeability and high radionuclide retention. Bentonite is one such clay used in containers to isolate waste and prevent leakage. Researchers at Sandia National Laboratories have been investigating the properties of various types of clay to improve the isolation containers and improve their calculations regarding the best method for long-term [millions of years] storage of nuclear waste.

One chemical mechanism researchers have been focusing on is the reaction between iodine 127 iodides and bentonite clay. As they are both negatively charged, one would expect they would repel each other, but on the nanoscale, in between the layers of clay, water enhances the formation of pairs of iodide ions. The resulting neutrally-charge molecule that isn’t repelled by the bentonite clay. Still, in spite of testing procedures, part of which involved smashing the clay, bentonite is a better storage medium than was previously thought. Researchers also found that kaolinite clay was even better at isolating iodine 127.

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