New quaternary additive for processing fully ceramic microencapsulated fuels without applied pressure

To apply SiC ceramics as a matrix for fully ceramic microencapsulated (FCM) fuels, the equivalent boron content (EBC) factors of elements in the sintering additives should be considered as an important criterion. A previously developed quaternary additive composition based on AlN–Y2O3–Sc2O3–MgO contained Sc, which has a relatively high EBC factor (8.56 × 10−3). This study proposes a novel quaternary additive composition (AlN–Y2O3–CeO2–MgO), in which Sc is replaced by Ce (EBC factor = 6.36 × 10-5). The new additive composition achieved successful densification of the SiC matrix at 1850 °C without applied pressure. FCM pellets containing 36 vol% tristructural isotropic (TRISO) particles were successfully sintered at 1850 °C using the above matrix without applied pressure. The thermal conductivities of the FCM pellets prepared via pressureless sintering with 36 vol% TRISO particles were 43.9 W·m-1·K-1 and 25.8 W·m-1·K-1 at 25 °C and 500 °C, respectively.