Thermal conductivity of (Np0.20Pu0.50Am0.25Cm0.05)O2−x solid solutions

Highlights: • Thermal conductivity of (Np0.20Pu0.50Am0.25Cm0.05)O2−x was evaluated. • Dependence of thermal conductivity on storage time was clarified. • Results were discussed with the lattice expansion model by self-irradiation. • After annealing at 1423 K in vacuum, thermal conductivity returned. -- Abstract: The authors prepared the sintered sample of (Np0.20Pu0.50Am0.25Cm0.05)O2−x (2 − x = 1.98, 1.96) solid solution and evaluated the dependence of the thermal conductivity on storage time and temperature. The heat capacity of (Np0.20Pu0.50Am0.25Cm0.05)O1.98 was measured between 324 and 1082 K by a drop calorimetry. The thermal diffusivity of (Np0.20Pu0.50Am0.25Cm0.05)O1.98 was measured when the storage time became 48, 216, 720 and 1584 h and that of (Np0.20Pu0.50Am0.25Cm0.05)O1.96 was measured when the storage time became 0,528 and 1386 h. In this study, the latter sample was annealed at 1423 K in vacuum with background pressure of less than 2.0 × 10−4 Pa just after the measurement on the storage time, 1386 h. The thermal diffusivity of (Np0.20Pu0.50Am0.25Cm0.05)O1.96 just after annealing returned to the values of the storage time, 0 h. This result reveals the thermal recovery behavior by annealing. The thermal conductivity of (Np0.20Pu0.50Am0.25Cm0.05)O2−x was determined from the measured thermal diffusivity, heat capacity and bulk density. The thermal conductivity of (Np0.20Pu0.50Am0.25Cm0.05)O2−x exponentially decreased with increasing storage time. This result suggested that the decrease of the thermal conductivity was attributed to the accumulation of lattice defects caused by self-irradiation