Optimizing Acoustic Cavitation of Tristructural-Isotropic (TRISO) Fuel Particles for Efficient Recovery of Inner Uranium Kernels in Nitric Acid

High-power acoustic sound waves were delivered to an aqueous media containing tristructural-isotropic (TRISO) fuel particles to penetrate the multiple layers of the particles and access the uranium fuel kernels for recovery. The most challenging layer to penetrate was silicon carbide (SiC), which acts as a pressure vessel to trap gaseous fission products from release during operation in a reactor core. These studies demonstrate the first ever successful recovery of uranium from TRISO particles using acoustic cavitation, offering a simplified, cost-effective option for HALEU recovery from used, short-burned, defective, or off-specification TRISO particles. Initial attempts proved successful in a 0.1 M nitric acid medium by producing a 5% uranium recovery after 40 h of sonication. An acid concentration dependence on uranium leaching from compromised particles was observed. A ≈70% uranium recovery was demonstrated in 6.0 M HNO3 after 55 h of sonication. Scanning Electron Microscope (SEM) images were obtained on partially damaged TRISO particles to visualize the direct effect of cavitation. The images revealed three types of damage to the TRISO particles: (1) complete removal of all TRISO layers, (2) obliteration to portions of the carbon and SiC layers, and (3) channeling through the SiC layer and subsequent carbon layers to the uranium centers.