TRISO

Production

TRISO fuel is most commonly fabricated using the sol-gel process, developed at Oak Ridge National Laboratory in the United States. First, uranium or thorium is dissolved using nitric acid, and ammonia is used to precipitate UO₂ or ThO₂ ("sol"). The sol is then sprayed through a heated organic liquid, where the surface tension forms tiny gel spheres. To form UCO, carbon is dispersed through the gel to promote formation of UC₂. Fluidized-bed chemical vapor deposition is then used in several steps to apply the porous carbon, inner PyC, SiC, and outer PyC coatings. The finished TRISO particles are then embedded in a matrix of graphite and resin, then heated and pressed.