Graphite is used to maintain the fission chain reactions in some types of widely used nuclear reactors. It is estimated that there are about three hundred thousand tons of nuclear graphite waste awaiting disposal around the globe. Because they have a high density of legacy reactors, about one third of the irradiated graphite waste in the world is in the U.K.
     Abbie Jones works at the University of Manchester. She said “Most of the advanced nuclear reactor technologies being proposed for future low carbon energy production will also use nuclear graphite, so this waste burden is likely to increase for future generations unless novel solutions are examined to treat, reduce and recycle this waste form. Technologies that can minimize this burden will not only massively reduce costs of managing legacy wastes but also improve the sustainability of future nuclear reactors and help achieve net zero targets.”
     The current strategy of the U.K. is to store waste graphite temporarily in order to allow short-lived isotopes to decay prior to final disposal. This strategy was handed down from the U.K. Nuclear Decommissioning Authority. However, storing nuclear graphite waste is costly, space-inefficient and carries the risk of radioactive contamination.
     In response to these issues, Jones and her colleagues investigated whether electrolysis in high-temperature molten salt solutions could be used to decontaminate nuclear graphite. Clint Sharrad is one of the Manchester team. He said that they chose to utilize molten salt because it has a wide electrochemical window. This allows them to access electric potentials that could better force nuclear graphite contaminant removal.
     As proof of concept, the team carried out tests using graphite samples from different reactor sites across the U.K. Following electrolysis, they analyzed what corrosion and fission products the graphite released into the molten salt media. The team then adjusted their process parameters to optimize radioisotopes transfer into the salt phase. After the treatment, the team evaluated the graphite and found that there had been a significant reduction in the radioactive content. The decrease in radioactive processes in the graphite was sufficient to reclassify the remaining graphite from intermediate-level waste to low-level waste.
      Ken Czerwinski is a radiochemist at the University of Nevada, Las Vegas in the US. He says that the “key contribution of this work is the potential to concentrate radioactive waste and limit the amount of material destined for high-level radioactive waste disposal.”
       Jones suggested that if they can apply this new method on an industrial scale, it “could save the UK over £1 billion” in costs related to managing legacy nuclear graphite by “avoiding interim storage requirements and minimizing waste volumes requiring managed disposal”.
     The researchers observed that there was minimal degradation in the graphite in spite of achieving high decontamination levels. This suggests that it may be possible for future reactors to reuse the decontaminated graphite. Sharrad says that this would result “not only reducing the waste burden but also enhance the sustainability of nuclear reactor systems by providing a whole lifecycle approach for a main reactor core component.”
    The next step of the Manchester team is to conduct follow-up research to look at a broader variety of graphite samples and to explore whether treated graphite will perform as well as virgin graphite in a reactor system. This will enable them to determine whether reusing nuclear graphite may be a feasible option in the future.