Coolant solubility of burnable neutron absorbing material: A thermodynamic treatment in support of advanced CANDU reactor fuel.

摘要

Advanced CANDURTM Reactors (ACR-1000) are expected to be the next generation of Canadian nuclear power technology. The ACR-1000 will employ a newly designed fuel bundle similar in appearance to those used in current CANDURTM reactors. Isotopically enriched uranium dioxide fuel and a Burnable Neutron Absorbing (BNA) central element composed of stabilized zirconia (ZrO2 s) doped with gadolinia (Gd2O 3 s) and dysprosia (Dy 2O3 s) will be used. As the BNA material contains elements with high neutron absorption cross sections, there is a safety concern with the possible leaching of these elements into the light water coolant, in the unlikely event of a breach in the Zircaloy sheath.;To address this concern, solubility measurements in water over a range of pH values have been conducted on pure dysprosium and gadolinium oxide to determine the extent of dissolution in relation to the possible presence of complex ions involving OH-. Experimentation has led to estimated thermodynamic properties for aqueous ions and complex ions, and revised Pourbaix diagrams and, in general, a framework to connect BNA solubility with other thermochemical fuel treatments. The conclusion is reached that negligible concentrations of dissolved dysprosium and gadolinium species are expected to develop in the alkaline aqueous coolant, characteristic of the ACR-1000.