Microstructure and thermal conductivity of fully ceramic microencapsulated fuel fabricated by spark plasma sintering

Abstract Fully ceramic microencapsulated pellet ( FCM ), consisting of tristructural isotropic ( TRISO ) particles embedded in silicon carbide (SiC) matrix, was fabricated using spark plasma sintering. The parameters affecting the densification of SiC matrix were first investigated, and then FCM pellets were prepared using TRISO particles with/without outer pyrolytic carbon ( OP yC) layer. Effects of thermal exposure on the TRISO particles during SPS were evaluated. In addition, the thermal condcutvitities of FCM pellet, as well as the SiC matrix, were measured using laser flash. It was revealed that the TRISO particles with OP yC layers significantly lower the thermal conductivity of FCM pellet. Based on Maxwell‐Eucken model, the predicted effective thermal conductivities of TRISO particles with/without OP yC layers were 14.4 W/m K and 25.2 W/m K, respectively. Finite elements simulation indicated that the SiC layer in TRISO particle plays a dominant role on the thermal conductivity of FCM . The presence of OP yC layers would generate gaps/porous SiC near the interface and resist the heat flows, leading to a lower thermal conductivity of FCM.