Mixed RuO₂/TiO₂/PtO₂-Coated Titanium Anodes for the Electrolytic Dissolution of Nuclear Fuels

Titanium anodes with coatings of mixed oxides of RuO₂ and TiO₂ and RuO₂, TiO₂, and PtO₂ are prepared by a thermal decomposition method, which consists of applying coating solutions containing salts of ruthenium, titanium, and platinum over a pretreated titanium surface, drying, and heat treating at 775 K for 1 h. X-ray diffraction studies on these samples confirm the presence of oxide phases of RuO₂, rutile TiO₂, and PtO₂ over the surface. Scanning electron microscope observations show that the microcracks in the coating decrease as the RuO₂ content is increased and that the PtO₂ overlay generally has fewer microcracks. X-ray photoelectron spectroscopy analyses indicate the presence of ruthenium as Ru⁴⁺, titanium as Ti⁴⁺ and platinum as elemental platinum as well as Pt²⁺ and Pt⁴⁺ in the coating. Testing of these anodes during the electro-oxidative dissolution of UC and (U,Pu)C in an HNO₃ medium containing cerium nitrate indicates that the anode with a lower RuO₂ content can be used only up to 340 K, whereas with an increase in the RuO₂ content as well as with an overlay of PtO₂, the anodes can be used even in a boiling nitric acid medium with improved cell performance.