Structural investigation of thorium in molten lithium-calcium fluoride mixtures for salt treatment process in molten salt reactor |
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Authors: | Masahiko Numakura Nobuaki SatoCatherine Bessada Yoshihiro OkamotoHiroshi Akatsuka Atsushi NezuYasuaki Shimohara Keisuke TajimaHirokazu Kawano Takeshi NakahagiHaruaki Matsuura |
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Affiliation: | a Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1-N1-10, Ookayama, Meguro-ku, Tokyo 152-8550, Japan b Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan c Conditions Extrêmes et Matériaux: Haute Température et Irradiation, CNRS-UPR 3079, 1D Avenue de la Recherche Scientifique, 45071 Orléans cedex 2, France d Japan Atomic Energy Agency, Kansai Photon Science Institute, Kouto 1-1-1, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan |
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Abstract: | X-ray absorption fine structure (XAFS) measurements on thorium fluoride in molten lithium-calcium fluoride mixtures and molecular dynamics (MD) simulation of zirconium and yttrium fluoride in molten lithium-calcium fluoride mixtures have been carried out. In the molten state, coordination number of thorium (Ni) and inter ionic distances between thorium and fluorine in the first neighbor (ri) are nearly constant in all mixtures. However the fluctuation factors (Debye-Waller factor (σ2) and C3 cumulant) increase until xCaF2 = 0.17 and decrease by addition of excess CaF2. It means that the local structure around Th4+ is disordered until xCaF2 = 0.17 and stabilized over xCaF2 = 0.17. The variation of fluctuation factors is related to the number density of F− in ThF4 mixtures and the stability of local structure around Th4+ increases with decreasing the number density of F− in ThF4 mixtures. This tendency is common to those in the ZrF4 and YF3 mixtures. However, in the case of YF3 mixtures, the local structure around Y3+ becomes disordered until xCaF2 = 0.40 and it becomes stabilized by addition of excess CaF2. The difference between ThF4 mixtures and YF3 mixtures is related to the difference of Coulumbic interaction between Th4+-F− and Y3+-F−. Therefore, the variation of local structure around cation is related to not only number density of F− in molten salts but also the Coulumbic interaction between cation and anion. |
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Keywords: | Molten salt reactor X-ray absorption fine structure Molecular dynamics simulation Thorium fluoride Lithium fluoride Calcium fluoride |
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