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The interaction between UN and CdCl2 in the LiCl-KCl molten eutectic was studied at 773 K.The reaction was controlled by sampling the melt, as well as by analysis of the resulting precipitate. The process was shown to proceed according to several parallel reactions. The summary reaction was determined to have two stages: a fast one and a slow one. The 19–53% UN → UCl3 conversion was obtained for the molar ratio of CdCl2/UN = 1.22–14.9. The rest of UN converts into the precipitate of complex composition (UNCl + U2N3 + U4N7 + UN2). The increase in the CdCl2/UN molar ratio from 1.22 to 14.9 resulted in the decrease in duration of the first “fast” stage of the process from 18 h to 1 h. Keywords: Spent nuclear fuel, Nitride nuclear fuel, Chlorination, Pyrochemistry, UN, UNCl, Molten salts

Nitride nuclear fuel (UN + 10-20% PuN) is considered a promising alternative to the widely used oxide nuclear fuel (UO2). Thermal conductivity and density of nitride fuel are ∼ 7 times and 1.3 times higher than that of oxide fuel, respectively. Nitride fuel demonstrates a good compatibility with the cladding of fuel rods made of stainless steel. Along with the development of new fuel, methods for its subsequent processing are being developed. Various options for the initial opening of nitride spent nuclear fuel (SNF) are considered in this article. The use of gaseous chlorine is technologically inconvenient and dangerous when working with radioactive substances. The electrochemical dissolution of nitride SNF cannot be realized due to the formation of a by-product - UNCl. Uranium nitride chloride is an insulator and it blocks the electrochemical process. It was found that the chlorination of nitride SNF with cadmium or lead chlorides makes it possible to carry out 100% UN → UCl3 conversion. The use of voloxidation (oxidation of nitride SNF to oxides) as the first stage of processing will make the entire technology universal, suitable for processing both nitride and oxide SNF. The choice of the method for opening SNF depends on the choice of the subsequent stages of its processing. Keywords: nitride spent nuclear fuel, SNF, chlorination, anodic dissolution, UNCl, “soft” chlorination, voloxidation, processing