Interaction between uranium-plutonium mixed oxide and zircaloy-2

Currently there is considerable interest in the utilisation of zircaloy-clad mixed U-Pu oxide as fuel for thermal reactors. Thermodynamic calculations predict that zircaloy can easily reduce PuO2 to Pu2O3 and this has been confirmed experimentally. However, mixed oxide is expected to behave differently in this respect. The present investigation is an attempt to study, out-of-pile, the extent of chemical reaction between U-Pu oxide and zircaloy-2. Although the thermal reactor fuels generally contain a low percentage of PuO2(<5%PuO2), a mixed oxide containing 20%PuO2 was chosen for this study to enhance the possibility of reaction. It was assumed that if no reaction takes place with this composition none would occur with those containing less PuO2. With a view to keeping the reactants in close proximity, the experiments were carried out on composite pellets made from powdered sintered mixed oxide and zircaloy filings. Some composite pellets of pure PuO2 and zircaloy were also included in the study as an extreme case of reactivity. (Auth.)