Relation between a fuel rod failure cause and a reactor coolant radioactivity variation

The reactor coolant radioactivity in the coolant caused by unstable fission products released into the coolant depends usually on fuel burnup, fuel rod power, cladding defect size and its axial location, and coolant letdown flow rate. In this study, taken into account are three main fuel rod failure causes for PWRs in Korea that include debris-induced fuel failure, grid-to-rod fretting wear-induced one and excessive cladding oxide-induced one. Characteristics of reactor coolant radioactivity variations of xenon and iodine specific to each fuel rod failure cause have been analyzed by considering fuel burnups at the fuel failure outset, cladding through-hole sizes and their axial locations, letdown flow rate, and steam-induced UO2 pellet oxidation along with interlinked fraction of fission gas bubbles. It was found that there exists an outstanding relation between a fuel failure cause and its relevant coolant radioactivity variation of xenon and iodine. The relation found in this study may be utilized proactively to predict a certain fuel rod failure cause during the reactor operation, which can provide utilities with an extra time enough to provide a countermeasure(s) against the predicted fuel failure cause and consequently eliminate such the fuel failure for the upcoming next cycle.