Behavior of Nb2O5 doped UO2 fuel in reactivity initiated accident conditions

This report describes the results of reactivity initiated accident (RIA) experiments using UO2 fuel pellets containing 0.29 w% Nb2O5 additive. In the present experiment, internal pressure of fuel rod, axial elongation and surface temperature of cladding were measured. From the result of post-irradiation examinations such as visual inspection, dimensional measurement and ceramography, fuel failure threshold and failure mechanism were explored. The results obtained were: (1) Failure threshold of the Nb2O5 doped fuel was equal to or greater than that of NSRR experimental data which were adopted in the Licensing Guideline for RIA, Japan. (2) Failure mechanism of the Nb2O5 doped fuel was local ballooning followed by cladding rupture. No significant differences in the failure mechanism existed between the doped and undoped prepressurized fuels, the latter used in previous NSRR experiments. (author)