Spent Fuel Reprocessing for Molten Salts Fast Neutron Reactors

Spent fuel still contains valuable materials such as uranium, plutonium and minor actinides that can be used to produce a new molten salt fuel. To do this, the spent fuel must be reprocessed to separate the reusable material from the final waste, which must be packaged in a matrix such as borosilicate glass for long-term storage. Several reprocessing options are being considered: - Option 1: Spent fuel salt dissolution in nitric acid to make it compatible with the Orano La Hague spent fuel reprocessing plant. The presence of chlorine must be limited, particularly to avoid corrosion, before mixing the solutions resulting from the dissolution of NAAREA spent fuel salt with the dissolution solutions usually processed at the La Hague plant. Thus, a chlorine precipitation step with silver, for example, could be added before reprocessing. The presence of sodium should also be limited or, at a minimum, the solutions resulting from the dissolution of NAAREA spent fuel salt must be diluted with solutions from the reprocessing of light water reactor fuels to ensure a sodium content compatible with the vitrification process. After reprocessing, the uranium and plutonium would be reused for a new fuel salt production and the final waste would be packaged in a glass matrix for long-term storage, as is done for the final waste from the light water reactor (LWR); Option 2: Since the spent fuel salt of NAAREA is composed of about 50% by weight of NaCl, and the chlorine could be enriched, it seems interesting to separate the NaCl before reprocessing the spent fuel salt. For this, precipitation of species other than NaCl via the use of a mixture of gas or carbonate directly into molten salt followed by a separation step such as filtration or vacuum distillation could be added. The precipitated and separated species (such as actinides and fission products) would then be dissolved in nitric acid to make them compatible with the Orano La Hague spent fuel reprocessing plant. The spent fuel salt reprocessing, without chloride and sodium, would be simplified. After reprocessing, the uranium and plutonium would be reused for a new fuel salt production and the final waste would be packaged in a glass matrix for long-term storage, as is done for the final waste from the light water reactor (LWR); - Option 3: Spent fuel salt reprocessing by a pyrochemical process where reusable materials (NaCl, PuCl₃, UCl₃, chlorides of minor actinides) are separated from molten salt and directly reused to produce a new molten salt fuel. Fission products (considered as a final waste) would be encapsulated in a suitable matrix for long-term storage such as borosilicate glass matrix. This treatment could be carried out in the vitrification workshops of the Orano La Hague plant after a nitric acid dissolution step. Options 1 and 2 do not allow reusable materials to be directly recycled, i.e. it requires the addition of a hydrometallurgical process between 2 molten salt steps (management of used fuel salt and new fuel salt fabrication). However, these options can be deployed in the short to medium term after some research and development studies. Option 3 seems more optimal because it allows reusable materials to be recycled directly. However its implementation seems possible only in the medium/long term after more substantial research and development