Thermal expansion of TRU nitrides as the fuel materials for transmutation of minor actinides

Takano, Masahide ; Akabori, Mitsuo; Arai, Yasuo; Minato, Kazuo 

As the research activities concerning the nitride fuel for the transmutation of minor actinides, the lattice thermal expansions of the transuranium nitrides were investigated in order to build the material database. The lattice parameters of NpN, PuN and AmN were measured by the high temperature X-ray diffraction method from room temperature to 1478 K. Their linear thermal expansions were determined as a function of temperature. The average thermal expansion coefficients over the temperature range of 293 to 1273 K for these nitrides were 8.8, 11.1 and 11.210 K, respectively. Further, the thermal expansions of the nitride solid solution samples, (Np,Am)N, (Pu,Am)N, (Np,Pu,Am,Cm)N and (Pu,Am,Zr)N, were measured to investigate the composition dependence. It was confirmed that the average thermal expansion coefficients for these solid solution samples could be approximated by the linear mixture rule within the error of 23%.