Development of fuel debris treatment technology by the fluorination method

The past severe accidents have occurred at several nuclear power plants (TMI-2, Chernobyl, and Fukushima Daiichi), and fuel debris was generated. As fuel debris contains many kinds of materials such as fissile, radioactive, and exothermic nuclides (or elements), criticality control, shielding, cooling and deterioration prevention are necessary for the management of fuel debris. The accountancy of nuclear materials (Pu and U) is also important. To manage these issues, we have been developing the fuel debris treatment technology using fluorination method. This technology mainly consists of three processes: (1) fluorination (the separation of U and Pu fluorides from non-volatile impurities), (2) recovery of U and Pu fluorides, and (3) oxide conversion. As many impurities are co-existed in fuel debris, rough separation of these impurities is effective for volume reduction of nuclear waste and precise accountancy of Pu and U. Moreover, converted oxides are stable, easy to be dissolved by nitric acid, and suitable for long term storage, reprocessing, vitrification, and disposal. The authors conducted fluorination experiments using several kinds of simulated debris to show the applicability of this technology to fuel debris treatment, and discussed about these results in this paper.