A logical approach for zero-rupture Fully Ceramic Microencapsulated (FCM) fuels via pressure-assisted sintering route

A pathway to Fully Ceramic Microencapsulated (FCM™) fuel pellets showing absence of sintering-derived “rupture” has been demonstrated. In the typical FCM manufacturing process, TRistructral ISOtropic (TRISO) particles show statistically significant rupture, caused by contact of particles during the axial shrinkage of fuel pellet that accompanies pressure-assisted sintering. To solve this, template SiC powder discs were fabricated to host planes of TRISO particles, and the disks were stacked to form a cylindrical “green” pellet. After sintering, up to ∼34% packing fraction of particles (Vp) was physically feasible without contact between planes. Sintering was shown to reduce the axial displacement between planes of TRISO particles, and X-ray Computed Tomography (XCT) showed planes separated by a displacement of ∼100 μm. XCT, optical microscopy and SEM showed the very limited radial displacement of particles. However, the relative density of the FCM pellet was limited to ∼95%. The current results support the zero-rupture concept as viable, but perturbations to TRISO arrangements and limited matrix density require further investigation to improve FCM fuel uniformity and microstructure.