Fuel-clad interactions: Uranium nitride and uranium dioxide with FeCrAl and Ti-modified stainless steel

Abstract

This study elucidates on the compatibility of fuel and clad materials for potential use in lead cooled fast reactors. Diffusion couples were performed on representative, unirradiated fuel forms (UN and UO2) with potential cladding materials, a Ti-modified stainless steel (D9) and a FeCrAl alloy (Kanthal APMT). Temperatures of 800–1200°C, with durations up to 100 h, were investigated. Chemical interaction between all combinations of the fuel and cladding candidates was found to be minimal, with no diffusion gradients observed or extensive interface phases formed. When interaction occurred, it was in the production of a minor discrete phase. At the highest temperatures, D9 with UN resulted in the formation of a Ti-C-N phase. D9 with UO2 resulted in the formation of a Ti-C-O phase. FeCrAl with UN resulted in the formation of an Al-N phase. FeCrAl with UO2 results in the formation of an Al-O phase. Despite the observed mechanical bonding between fuel and cladding material, no evidence of any chemical interaction with the uranium in the fuel material was found. At the higher temperatures investigated (>1000°C) there was evidence of clad softening resulting in transfer of material to the fuel surface.