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 NdCl
3 as an imitative substance in place of UCl
3 or PuCl
3 the phase diagram of NdCl
3-NaCl binary system was constructed.
Anhydrous neodymium chloride (NdCl
3) 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 NdCl
3-NaCl system, an intermediate compound of 3NdCl
3·NaCl, which decomposes at 540°C to NdCl
3 and liquid, and a eutectic at 437°C were found. The crystal structure of 3NdCl
3·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 UCl
3 and PuCl
3, and their thermochemical behavior is very similar to one another. Taking that into account, it is considered that the phase diagrams for UCl
3-NaCl and PuCl
3-NaCl systems should be reexamined.
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