Advancing coated particle fuel technology

Ogawa, Toru; Sawa, Kazuhiro

More stringent conditions of higher burnups and higher fuel temperatures of VHTR have prompted R&D of two types of fuel concepts: (1) conventional but more robust Triso design, and (2) ZrC-Triso. As for the conventional Triso, modeling efforts are focused on the palladium attack of SiC and the Ag diffusion through SiC. Concerning the fast migration of Ag through CVD-SiC, a self-mediated percolation diffusion model has been developed. There, attention is given to peculiarities of the CVD SiC grain boundaries. The ZrC-coated particle fuel has shown promising results particularly for its durability at temperatures beyond the 1600C criteria of the conventional Triso particles. The positron annihilation spectroscopy is applied to better define the quality of ZrC coating. One drawback of ZrC coating is rather large diffusion coefficient of ruthenium, possible mechanism of which is briefly discussed also.