Masayuki Murabayashi

Measurement of thermal properties of nuclear materials by laser flash method

The present status and prospects of the laser flash method for the measurement of thermal properties of nuclear materials are reviewed. Special emphasis is placed on the progress seen in experimental techniques for obtaining precise data on heat capacity and thermal diffusivity from 80 to 1,000 K. In this temperature range, the heat capacity and the thermal diffusivity of ceramic nuclear materials can be determined within a precision of ±2%. The data on heat capacity and thermal conductivity determined by the laser flash method are presented and discussed in respect of such nuclear materials as U02 U4O9 ThO2 BeO, ThO2-UO2 ThO2-Ce02 UO2-ZrO2 ThO2-Be0, UC, UN, US, UP, UC1-xNx and UP1-xSx.

Uranium mononitride: Heat capacity and thermal conductivity from 298 to 1000 °K

Abstract The heat capacity and the thermal diffusivity of uranium mononitride were measured by a laser flash method at temperatures ranging from 298 to 1000 °K. The samples were arc-melted UN having nearly zero porosity and sintered UN having porosity of 10.1%. The heat capacity of UN was represented by C p = 12.08 + 2.548 × 10 − 3 T − {−1.252 × 10 5 T −2 cal/mol · deg K (298–1000 °K)}. From the heat capacity data, entropy, enthalpy and the Gibbs energy function of UN were calculated. The thermal conductivities of arc-melted UN, calculated from the heat capacity and the thermal diffusivity data, at 350 and 1000 °K were 0.031 and 0.045 cal/ cm · sec · deg K, respectively. The results agreed reasonably well with those of Moore et al. obtained at lower temperatures.

Thermal conductivity of uo2 and u4o9 from 100 to 300 k

Abstract The thermal diffusivities of UO 2 and U 4 O 9 were measured by the laser flash method at temperatures ranging from 100 to 300 K. The phonon mean free path and the thermal conductivity were calculated from the obtained thermal diffusivity data and the heat capacity. The structure of the u 4 o 9 is closely related to the UO 2 structure with an excess oxygen atom per unit cell in U 4 O 9 . As the excess oxygen atoms increase the anharmonicity of the lattice vibration, the phonon mean free path in U 4 O 9 decreases. Therefore, the thermal conductivity of U 4 O 9 is much lower than that of UO 2 and increases slightly with increasing temperature due to the rise in heat capacity.