State of fuel elements with artificial through defects after testing in air at temperature of 350 °c

The behavior of fuel rods with E110 (Zr - 1% Nb) cladding, spent in fuel assemblies in the VVER-1000 reactor to a fuel burnup of 62 MW·d / kgU, has been studied under conditions simulating an abnormal situation during dry storage: air ingress into the fuel rod through primary through defects in the cladding and its interaction with the fuel. The through defects are located at different heights relative to the fuel kernel: in one fuel rod they are at the bottom of the cladding, in the other they are in the section corresponding to the middle of the fuel column. The defect state, its dimensions, fission product yield, their distribution in the fuel, fuel fragmentation, cladding structure and mechanical properties and zirconium hydride orientation were studied. It is shown that in places where the air environment penetrates through artificial slots into the fuel elements, additional oxidation of uranium dioxide occurs, accompanied by an increase in its volume, which leads to a local increase in the diameter of the cladding and the width of the defect, as well as the release of gaseous fission products.