Ryuzo Takagi

The structure of molten and simulated with polarizable- and rigid-ion models

Molecular dynamics (MD) simulations of molten were carried out using the polarizable-ion model (PIM) and the rigid-ion model (RIM). In these simulations the Born-Mayer-Huggins potential was employed with the same potential parameters for both models. In the PIM the polarization of the chloride ions was supplemented. Although the partial radial distribution functions (rdfs) between Dy and Cl, and between Cl and Cl are very similar for the two models, the rdf between Dy and Dy is quite different. The rdf between Dy and Dy experimentally determined by the isotope substitution method was well reproduced by the PIM. The strong Coulomb interaction between and is screened by the polarization of ions and the interaction distance between and becomes smaller than that given by the RIM. MD simulations for were made similarly. The PIM also reproduced the experimental total structure factor very well.

Structural determination of molten NaNO3, NaNO2 and their eutectic mixture by molecular dynamics simulation and X-ray diffraction

Molecular dynamics (MD) simulation was carried out for the molten NaNO3, NaNO2 and their eutectic mixture systems to compare their simulated structures with those determined experimentally by X-ray diffraction. As for the pure NaNO3 and NaNO2, parameters for repulsion potential were adjusted so that the structure factors of their simulated systems coincide reasonably with the corresponding experimental ones. The MD simulation of the mixture was carried out with the parameters determined for the component salts. The structure factor of the simulated mixture system successfully reproduced the experimental one, which shows validity of the proposed pair potential. The assignment of most of the peaks in the experimental correlation function was performed with the aid of simulated results. The simulated data has been used to determine the diffusion coefficients of the component ions.

Molar volume variation and ionic conduction in molten ErCl3NaCl and ErCl3KCl systems

Molar conductivities (Λ) of molten ErCl3NaCl and ErCl3KCl systems were evaluated using the data of molar volume, Vm, and conductivity, ϰ, which were measured as a function of the mole fraction of ErCl3 and temperature, by dilatometry and a conventional a.c. technique, respectively. The Λ values of molten ErCl3 were smaller than those of molten YCl3, in which a loose disordered network of edge-sharing octahedral units has been reported to exist. The Λ values of ErCl3NaCl and ErCl3KCl systems increased with decreasing ErCl3 concentration, x, and in the range x >4 0.25 the increment in Λ with x was much smaller than that in the range of x < 0.25. In a series of molten rare earth chlorides, Λ values have been found to be affected qualitatively by cationic radii and the types of linkage, that is, corner- or edge-sharing of octahedral units.

Structural determination of a molten (Li-K)Cl mixture of the eutectic composition by x-ray diffraction and molecular dynamics simulation

Abstract X-ray diffraction was performed for a molten (Li-K)CI mixture of the cutectic composition at 668 K. The three-dimensional structure of the melt was determined with the aid of molecular dynamics simulation.

Internal Cation Mobilities in the Ternary Molten System (Na, K, Cs)Cl

For molten (Na, K, Cs)Cl system, the relative differences in the internal cation mobilities at 1023 K are investigated by the Klemm method and the electric conductivity by a direct current method. From these data and the molar volumes which are evaluated from those of the pure salts on the assumption of additivity, the internal mobilities of the each cation, i.e., b Na , b K , and b Cs have been calculated. This result allows us to conclude that the internal mobilities of each cation become b Cs 0.6. In addition, the molecular dynamics simulation has been performed on molten (Na, K, Cs)Cl for the various compositions at 1023 K. Then, the self-exchange velocities (SEVs) of Na + , K + , and Cs + with reference to Cl - have been calculated. The sequence of the internal mobilities of these cations is well reproduced by the corresponding SEVs.

Phase diagram and Raman spectroscopy of EuCl2NaCl binary mixtures

Abstract A phase diagram of the EuCl 2 NaCl system was determined by differential scanning calorimetry (DSC) and the activity coefficients of EuCl 2 and NaCl in this system were estimated under some assumptions. According to DSC measurement, it was found that there were two phase transitions at 1123.9 K and 1016.8 K. In order to specify the melting point of EuCl 2 we did Raman spectroscopy experiments. Thus, the melting point of EuCl 2 was evaluated to be 1016.8 K which was detected as the lower peak in the DSC curve. Raman spectroscopy of this system suggested that complex species were not formed clearly in the EuCl 2 poor system and the estimated activity coefficients of EuCl 2 also supported this suggestion.

Continuous recovery of concentrated solute from the melt by countercurrent electromigration

Abstract On reprocessing spent metallic fuels in a molten salt bath it is very important to recover electrochemically base metals, such as Cs, Sr and Ba, from the salt bath repeatedly. For this purpose, we have investigated the internal mobilities of Cs in equimolar NaCl–KCl mixtures and the relative differences between the mobilities of Cs, Sr and Ba in the same solvent. From the view point of the technological aspects we designed an original countercurrent electromigration cell which is arranged to recover concentrated solute in the column from the melt. This electromigration method could be effectively used to separate multivalent cations from monovalent cations under the conditions of high current density, and the applicability of this new technique to cleaning the melt bath was demonstrated.

A fuel cycle concept for self-consistent nuclear energy system

Abstract A fuel cycle concept for Self-Consistent Nuclear Energy System which releases no fission products to the environment is proposed. Material and energy balances are shown for this system.

A molecular dynamics simulation of the electric properties in molten chloride and fluoride quaternary systems

The molecular dynamics simulation has been carried out on molten quaternary systems (Li, Na, K, Cs)Cl and (Li, Na, K, Cs)F at 973 K for the various compositions in order to investigate the electric properties, i.e. the self-diffusion coefficient, the self-exchange velocity and the relative differences in the internal cation mobilities of Cs in molten LiCl–NaCl–KCl eutectic and in FLINAK melts. These results allow us to conclude that the self-diffusion coefficients and self-exchange velocities of Li+, Na+, K+ and Cs+ with reference to Cl− and F− become almost similar tendencies for each composition. We found it possible to enrich at up to xCs=0.4∼0.5 in molten LiCl–NaCl–KCl eutectic and in FLINAK melts as well as LiCl–KCl equimolar mixtures.

Internal cation mobilities in the molten binary system Li2CO3K2CO3

Abstract Internal mobility ratios of two cations in the molten binary system (Li, K)(CO 3 ) 0.5 have been measured with the Klemm method. From these and available data on the densities and conductivities, the internal mobilities of Li + and K + have been calculated. Except at a region of relatively high concentration of Li 2 CO 3 , the Chemla effect occurs, that is, the mobility of the large cation K + is greater that of the small one Li + . The internal mobilities of Li + ions are well expressed by b Li = [ A /( V − V 0 )] exp (− E/RT ), where A , V 0 and E are constants characteristic of the cation and independent of temperature T , V the molar volume of mixtures, and R the gas constant. Negative deviations from this equation at a small V region may be attributed to the free space effect. For b K such a simple equation does not hold over an extended region of concentration, which suggests that the agitation effect and the free space effect would also play a role for the mobility.