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A TEAM of US researchers has developed a new material able to remove radioactive iodine gas from spent nuclear fuel.

The scientists, from the Sandia National Laboratory, used a metal-organic framework (MOF) – a crystalline material in which metals are bound to organic molecules – to capture the volatile gas. They say that their work could be used to help clean up nuclear accidents or in fuel reprocessing, where it’s vital to separate out long-lived isotopes like iodine. According to Tina Nenoff, a chemist at Sandia, the project “is one of the first attempts to use a MOF for iodine capture.”

At first, the team studied silver-loaded zeolite, a stable, porous mineral that was able to effectively trap iodine. Various other zeolite frameworks were also able to capture the radioactive gas with some degree of success, but the silver-loading dramatically improved its performance.

“Silver attracts iodine to form silver iodide,” explains Nenoff. “The zeolite holds the silver in its pores and then reacts with iodine to trap it.”

Silver, however, is prohibitively expensive to be used in this way, prompting Nenoff and her colleagues to try and engineer a cheaper material that could mimic, and even improve, its iodine-trapping natural properties. The team developed a MOF that took all the best elements of a zeolite – high surface areas, pores and stability – but specifically designed it to capture iodine.

“We’ve shown that MOFs have the capacity to capture and, more importantly, retain many times more iodine than current materials technologies,” says Argonne National Labaratory’s Karena Chapman, who contributed to the work.

The MOF, named ZIF-8, can be applied to spent fuel in either powder or pellet form – though the researchers say the powder has the unfortunate tendency to be blown around. Once it has trapped the iodine gas, the material can then be mixed into molten glass for long-term storage.