U-10Zr and U-5Fs: Fuel/cladding chemical interaction behavior differences

Abstract A fuel performance phenomenon that has previously limited the peak cladding temperature of metallic fast reactor fuel is fuel/cladding chemical interaction (FCCI). This study examined the differences in the phenomenon exhibited by the more recent fuel alloy, U-10Zr and a previously used fuel alloy, U-5Fs (Fs – fissium). Fs is comprised of Mo, Ru, Pd, Zr and Rh simulated fission products representing reprocessing carryover. Studies on the U-Zr alloy had shown the often controlling influence on FCCI of lanthanide (Ln) fission products (Ln: Ce, Nd, Sm, etc.) while a review of the U-Fs alloy behavior indicated a dominance of basic fuel/cladding interdiffusion (Fe, Ni with U). The recent studies on U-Zr fuel showed that migration of lanthanide fission products to the fuel/cladding interface facilitated the Ln dominance of FCCI behavior. This study was focused on understanding why Ln’s do not migrate in the U-5Fs alloy to the extent that they do in U-10Zr, or why they do not interact with the cladding like in U-10Zr fuel pins. A small fuel/cladding interaction layer was found containing the cladding and lanthanide components. However, it was also found that the lanthanide fission products are at least partially bound to agglomerates that also contained Pd, Rh and Zr, all minor components of Fs.