Thermal expansion and thermal conductivity of (Th,U)O-2 mixed oxides: A molecular dynamics and experimental study

PS Ghosh and PS Somayajulu and K Krishnan and N Pathak and A Arya and GK Dey, JOURNAL OF ALLOYS AND COMPOUNDS, 650, 165-177 (2015).

DOI: 10.1016/j.jallcom.2015.07.260

Thermal expansion and thermal conductivity of ThO2 and (Th,U)O-2 mixed oxides (MOX) have been investigated by using molecular dynamics (MD) simulation and experimental study. MD simulation have been performed to determine lattice thermal expansion of Th1-xUxO2 (x = 0 to 0.3125) solid-solutions in the temperature range of 300-3000 K using a combination of Coulomb-Buckingham-Morse and many-body potential model with partial ionic charges. Special quasi-random structures were employed to establish solid-solution configurations. Experimental verification of the lattice thermal expansion behavior is carried out on polycrystalline sample of ThO2 -x wt.% UO2 (x = 0, 6, 13, 25 and 30) MOX from room temperature to 1273 K in vacuum using high temperature X-ray diffraction (HT-XRD). Our combined MD simulations and HT-XRD measurements indicate that incorporation of UO2 in ThO2 systematically increases coefficient of thermal expansion but the rate of increase is higher in low UO2 composition range (< 13 wt.%). A comparative evaluation of the thermal properties of ThO2-6wt.% UO2 pellets prepared by coated agglomerate pelletization (CAP) process and powder metallurgy routes (sintered in Ar-8% H-2 atmosphere) have been performed with respect to micro-inhomogeneity, porosity, O/M and trace impurities. The thermal conductivity of ThO2 and ThO2-6 wt.% UO2 calculated under equilibrium condition by Green-Kubo formalism show good agreement with our experimental measurements. (C) 2015 Elsevier B.V. All rights reserved.

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