Recent findings on the oxidation of UO2 fuel under nominally dry storage conditions

This paper is an overview of fuel-storage demonstration experiments, supporting research on UO2 oxidation, and associated model development, in progress at AECL's Whiteshell Laboratories. The work is being performed to determine the time/temperature limits for safe storage of irradiated CANDU fuel in dry air. The most significant recent experimental finding has been the detection of small quantities of U3O8, formed over periods of one to several years in a variety of experiments at 150-170 deg C. Another important trading is the slight suppression of U3O8 formation in SIMFUEL and other doped U02 formulations. The development of a nucleation-and-growth model for U3O8 formation is discussed, along with available activation energy data. These provide a basis for predicting U3O8 formation rates under dry-storage conditions, and hence optimizing fuel storage strategies. (author)