Densification behaviour of UO2/Mo core-shell composite pellets with a reduced coefficient of thermal expansion

UO 2 /Mo composite pellets with enhanced thermal conductivity have been considered for the novel construction of high-safety fuel systems. UO 2 /Mo core-shell composite pellets with a reasonable porosity of 4–5% were fabricated by spark plasma sintering (SPS). In the SPS UO 2 /Mo composite, the majority of pores remained homogeneous in the UO 2 matrix, while it had a dense morphology in the continuous Mo channel for the heat conduction . The sintering behaviour of the UO 2 /Mo composite indicated that the incorporating Mo impeded densification of UO 2 , and the primary densification temperature ranged from 903 K to 1270 K. To introduce 2 vol% Mo to UO 2 , the thermal conductivity (TC) was enhanced to 4.02 W/m·K at 1073 K. The above result represented a 23.31% improvement over the value of 3.26 W/m·K (Fink) for a pure UO 2 pellet, which was approximated by the revised Hasselman-Johnson model. In particular, the coefficient of thermal expansion (CTE) was reduced to 10.0 × 10 −6 /K from 298 K to 1673 K, representing an 8.83% reduction from the value of 10.98 × 10 −6 /K (Martin) for a pure UO 2 pellet. The reduction effect on the CTE was superior to that of other UO 2 matrix composites fuel systems and, hence, offers an external safety aspect for reactors at the elevated temperatures close to accident conditions. These results provide a feasible method for the fabrication of a UO 2 /Mo core-shell pellet as an accident tolerant fuel.