TREAT testing of additively manufactured SiC canisters loaded with high density TRISO fuel for the Transformational Challenge Reactor project

Specimens composed of a novel nuclear fuel architecture underwent testing in the Transient Reactor Test Facility (TREAT) to investigate their behavior in thermomechanical states only possible with this type of testing. Uranium mononitride fuel kernels, with coatings typical of Tristructural Isotropic (TRISO) systems, were loaded into additively manufacturing silicon carbide (SiC) canisters and treated by chemical vapor infiltration so that the TRISO particles were held in a fully ceramic SiC matrix. A metallic heat sink capsule was used in TREAT to test fresh fuel specimens under progressively higher energy depositions. Thermomechanical modeling and post transient examinations, including a unique application of x-ray computed tomography, showed that more energetic transients led to stronger temperature gradients, higher stresses, and increased level of fracturing in the specimens. While some specimens were subjected to challenging conditions, the level of fracturing observed did not show a measurable dimensional change or loss of specimen geometry. These results indicate that this fuel architecture has resilience to catastrophic failure under power pulse transients. Future experiments are recommended for specimens which have been previously irradiated in order to investigate the effects of fuel burnup and neutron fluence on transient fuel performance.