Conference Proceedings Paper
PREDICTING THE BEHAVIOUR OF DEFECTED CANDU FUEL OXIDATION IN AIR WITH THE USA DOE SEMI-EMPIRICAL MODEL FOR THE OXIDATION OF DEFECTED LWR FUEL
13th International Conference on CANDU Fuel - 2016 Aug. 15-18
J. Freire-Canosa (NWMO (Nuclear Waste Management Organization))
Summary The USA Department of Energy (DOE) semi-empirical model that predicts the oxidation of defective LWR fuel in air to fuel cladding breaching was extended to predict the behaviour of defected CANDU fuel elements in air. Correlations were found for commercial defected CANDU fuel elements of average burnup (8.3 GWd/MTU) in the temperature range 25-350oC that predict the incubation time for fuel pellet oxidation to U3O8 leading to fuel cladding breaching. Predictions from these correlations were consistent with available experimental test data for irradiated CANDU fuel in the temperature range 200-400?C. For the only available data at lower temperatures (150?C) from the AECL Controlled Experiment (CEX-1, 1980-1996), the model predicted full conversion to U3O7/U4O9 in 14.8 years in agreement with the experimental value of 15.5 years. The model also indicated that when terminated in 1996, the CEX-1 experiment was about midway to cladding breaching due to oxidation of the pellets to U3O8. Therefore, the extension of the USA DOE semi-empirical model to CANDU fuel for oxidation of defected fuel elements appears validated by the data available from the AECL experiments in the range 150?C to 400?C. The results presented confirm the rationale as to why the USA DOE model can be extended to CANDU fuel and offer proof that it predicts well actual experimental values, particularly, below 200?C where the data is difficult to obtain because of the very long times needed to oxidize the pellets to U3O8 which is of the order of decades at 150?C and much longer below this temperature. Temperatures below 150?C are the temperatures relevant to CANDU fuel storage systems and the used fuel containers.
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