Thermal conductivity of near-stoichiometric (U, Nd)O 2, (U, Sm)O 2 and (U, Eu)O 2 solid solutions

Abstract

The thermal conductivities of near-stoichiometric (U, R)O 2 solid solutions (R = Nd, Sm and Eu) containing RO 1.5 up to 15 mol% were determined in the temperature range 700–2000 K by the measurement of thermal diffusivity. The thermal conductivities satisfied the phonon conduction equation K = ( A + BT) −1 within ± 5%. The constant A corresponding to the lattice defect thermal resistivity increased linearly with the rare earth element content, while the temperature coefficient B was almost independent of it. The change in A with the rare earth element content increased in order of (U, Eu)O 2, (U, Sm)O 2 and (U, Nd)O 2 solid solutions. The increase of A was explained reasonably by the lattice defect model considering U 4+, U 5+ and R 3+ ions in the solid solutions as phonon scattering centers, using a common value for the strain parameter ( ϵ = 110). For all solid solutions, the lattice strain effect on the lattice defect thermal resistivities was much larger than the mass effect. In addition, the effect of U 5+ ions on the lattice defect thermal resistivity caused by the lattice strain effect was larger than that of R 3+ ions.