Improvements in the performance of nuclear fuel particles offered by silicon-alloyed carbon coatings

Two-phase mixtures of pyrolytic carbon (PyC) and either silicon carbide or zirconium carbide are commonly called alloyed carbons and can be deposited on nuclear fuel particles by a combination of the well-known techniques of depositing carbon and the carbides. The silicon-alloyed carbons have properties that offer substantial improvements in coated-particle performance, while the zirconium-alloyed carbons that have been investigated have been found to be lacking in two of the properties essential for improved coating performance. The properties of the silicon-alloyed carbons that give rise to the improvements in performance are higher strength, smaller irradiation-induced dimensional changes, and a lower diffusivity for cesium than pure PyC's. These properties have significant implication to coated-particle design. Also, the silicon-alloyed carbons do not offer fundamental difficulties to the head-end of fuel reprocessing