Molten chloride mixtures are considered to be a fast-breeder-reactor fuel and a solvent in pyrochemica reprocessing of nuclear spent fuel. In this work, using NdCl3 as an imitative substance in place of UCl3 or PuCl3 the phase diagram of NdCl3-NaCl binary system was constructed. Anhydrous neodymium chloride (NdCl3) of 99.9% in purity, sodium chloride (NaCl) of 99.99% were used for the sample mixtures. Chloride mixtures were prepared by taking weighed amounts of the components prior to melting and freezing under dry inert atmosphere, and their compositions were determined considering loss in weight due to vaporization of NaCl. These mixtures were ground prior to use for differential thermal analysis (DTA) and X-ray diffractometry (XRD). Transition temperatures of each sample were obtained by DTA with heating curves at a rate of 15K/min in argon flowing at 100ml/min, and solid phases were characterized by XRD under dry nitrogen. In the NdCl3-NaCl system, an intermediate compound of 3NdCl3·NaCl, which decomposes at 540°C to NdCl3 and liquid, and a eutectic at 437°C were found. The crystal structure of 3NdCl3·NaCl was a hexagonal (of which lattice parameters were a0=7.50Å, c0=4.25Å at 22°C). Light rare-earth trichlorides have the same crystal structure as UCl3 and PuCl3, and their thermochemical behavior is very similar to one another. Taking that into account, it is considered that the phase diagrams for UCl3-NaCl and PuCl3-NaCl systems should be reexamined.
The density and ultrasonic velocity of NaNO3-MNO3 (M: Li, K, Rb and Cs) binary melts have been measured by means of the manometric method and the pulse transmission method with precisions of ±0.2% and ±0.1%, respectively. The molar volume, isentropic and isothermal compressibilities have been determined from the experimental results. The molar volumes of NaNO3-LiNO3, NaNO3-KNO3 and NaNO3-RbNO3 binary melts show almost additive value, while that of NaNO3-CsNO3 binary melts deviates positively from the additivity. Both the isentropic and isothermal compressibilities of the binary melts deviate positively from the additivity by 1-2%. It has been concluded that the mixing of NaNO3 and MNO3 causes slight deviation from the ideal behavior in molar volume and compressibility.
The ultrasonic absorption coefficient, α in NaNO3-MNO3 (M: Li, K, Rb, Cs) binary melts has been measured by means of the pulse transmission method in the frequency range of 15-65MHz with the precisions of 5%. The values of αf-2 showed no frequency dependence for all binary melts. The bulk viscosity of binary melts determined from the absorption coefficient shows the negative temperature dependence. The bulk viscosities of NaNO3-KNO3, NaNO3-RbNO3 and NaNO3-KNO3 binary melts decrease steeply with increasing NaNO3 content at MNO3 (M: K, Rb and Cs) rich sides. A calculation based on the relaxation theory has been applied for bulk viscosity of the binary melts. The bulk viscosity of the mixture was calculated by using the values of isentropic compressibilities and bulk viscosities of the component salts. The calculated values agreed well with the experimental values. It has been concluded that the structural rearrangement in the binary melts is controlled by the motion of the constituent having cations with smaller size and corresponding the shorter relaxation time in pure component melt.