State of Fuel Rods with Artificial Through-Wall Defects after Tests in Air at 350°C

Abstract—The behavior of fuel rods (FRs) with E110 alloy (Zr–1% Nb) cladding, which operated as part of fuel assemblies in a VVER-1000 reactor up to a fuel burnup of 62 (MW day)/kgU, is studied under the conditions modeling an off-normal situation during dry storage: air inflow into an FR through primary through-wall defects in the cladding and the interaction of air with the fuel. Through-wall defects are created at different heights relative to the fuel core: in the lower part of the cladding in a certain FR, and in the middle of the fuel column in another FR. The states of the defects, their dimensions, fission product release and distribution in the fuel, fuel fragmentation, the structure and mechanical properties of the cladding, and the orientation of zirconium hydrides are studied. Additional oxidation of uranium dioxide is shown to occur at the sites of air penetration into the FRs through artificial cuts; this is accompanied by an increase in its volume, which causes a local increase in the cladding diameter and the defect width and the release of gaseous fission products.