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Journal Articles

Structural investigation of thorium in molten lithium-calcium fluoride mixtures for salt treatment process in molten salt reactor

Numakura, Masahiko*; Sato, Nobuaki*; Bessada, C.*; Okamoto, Yoshihiro; Akatsuka, Hiroshi*; Nezu, Atsushi*; Shimohara, Yasuaki*; Tajima, Keisuke*; Kawano, Hirokazu*; Nakahagi, Takeshi*; et al.

Progress in Nuclear Energy, 53(7), p.994 - 998, 2011/11

 Times Cited Count:13 Percentile:70.01(Nuclear Science & Technology)

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 and inter ionic distances between thorium and fluorine in the first neighbor are nearly constant in all mixtures. However the fluctuation factors (Debye-Waller factor and C$$_3$$ cumulant) increase until $$x$$CaF$$_2$$ = 0.17 and decrease by addition of excess CaF$$_2$$. It means that the local structure around Th$$^{4+}$$ is disordered until $$x$$CaF$$_2$$=0.17 and stabilized over $$x$$CaF$$_2$$ = 0.17. The variation of fluctuation factors is related to the number density of F$$^-$$ in ThF$$_4$$ mixtures and the stability of local structure around Th$$^{4+}$$ increases with decreasing the number density of F$$^-$$ in ThF$$_4$$ mixtures. This tendency is common to those in the ZrF$$_4$$ and YF$$_3$$ mixtures.

Journal Articles

Ion specific effects on the structure of molten AF-ZrF$$_4$$ systems (A$$^+$$ = Li$$^+$$, Na$$^+$$, and K$$^+$$)

Pauvert, O.*; Salanne, M.*; Zanghi, D.*; Simon, C.*; Reguer, S.*; Thiaudi$`e$re, D.*; Okamoto, Yoshihiro; Matsuura, Haruaki*; Bessada, C.*

Journal of Physical Chemistry B, 115(29), p.9160 - 9167, 2011/07

 Times Cited Count:62 Percentile:81.7(Chemistry, Physical)

The structure of molten AF-ZrF$$_4$$ system (A$$^+$$=Li$$^+$$, Na$$^+$$, K$$^+$$) is studied using EXAFS spectroscopy with molecular dynamics simulations. From the Zr$$^{4+}$$ solvation shell point of view, we observe a progressive stabilization of the 7-fold and then of the 6-fold coordinated complexes when passing from Li$$^+$$ to Na$$^+$$ and K$$^+$$ as a "counterion". Particular attention is given to the systems consisting of 35 mol% of ZrF$$_4$$. At that particular composition, the ZrF$$_6$$$$^{2-}$$ complex predominates largely whatever the nature of the alkali. The calculated vibrational properties of this complex are in excellent agreement with a previous Raman spectroscopy experiment on molten KF-ZrF$$_4$$. The most important differences are observed for the lifetime of these octahedral units. On a larger scale, an intense first sharp diffraction peak is observed for the Zr$$^{4+}$$-Zr$$^{4+}$$ partial structure factor, which can be attributed to the correlations between the octahedral units formed.

Journal Articles

In situ experimental evidence for a nonmonotonous structural evolution with composition in the molten LiF-ZrF$$_4$$ system

Pauvert, O.*; Zanghi, D.*; Salanne, M.*; Simon, C.*; Rakhamatullin, A.*; Matsuura, Haruaki*; Okamoto, Yoshihiro; Vivet, F.*; Bessada, C.*

Journal of Physical Chemistry B, 114(19), p.6472 - 6479, 2010/05

 Times Cited Count:59 Percentile:79.63(Chemistry, Physical)

The structure of the molten LiF-ZrF$$_4$$ system up to 50 mol% ZrF$$_4$$ was investigated by combining high-temperature nuclear magnetic resonance (NMR) and extended X-ray absorption fine structure (EXAFS) experiments with molecular dynamics (MD) calculations. $$^{91}$$Zr high-temperature NMR experiments give an average coordination of 7 for the zirconium ion on all domains of composition. MD simulations, in agreement with EXAFS experiments at the K-edge of Zr, provide evidence for the coexistence of three different Zr-based complexes, [ZrF$$_6$$]$$^{2-}$$, [ZrF$$_7$$]$$^{3-}$$, and [ZrF$$_8$$]$$^{4-}$$, in the melt.

Oral presentation

Structural analysis of molten TbF$$_3$$-LiF

Numakura, Masahiko*; Bessada, C.*; Ory, S.*; Rakhamatullin, A.*; Akatsuka, Hiroshi*; Nezu, Atsushi*; Yaita, Tsuyoshi; Okamoto, Yoshihiro; Shiwaku, Hideaki; Matsuura, Haruaki*

no journal, , 

To investigate the local structure of molten TbF$$_3$$ - LiF (x[TbF$$_3$$ = 0.2), X-ray absorption fine structure technique (XAFS) was applied using by BL11XU in SPring-8. By several analyses, e.g. X-ray diffraction and differential scanning calorimetry, it had been confirmed that TbF$$_{3}$$ and boron nitride reacted at less than 1073 K even under helium gas flow environment, thus, we focused on the spectrum obtained below 1073 K. According to the curve fitting, the interionic distance obtained from the data of heating between 933 K and 1013 K was shorter than solid state. It would be surely molten state of TbF$$_3$$ - LiF (x[TbF$$_3$$] = 0.2), since the value of distance obtained, i.e. 2.26${AA}$ corresponds to the sum of ionic radii of Tb$$^{3+}$$ and F$$^-$$.

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