Immobilization of High－Level Radioactive Waste: III : Reactivity of Starting Materialsin Formation of Strontium Titanate

Titanates with the perovskite-type structure are expected as the most suitable materials which are capable of keeping the radwaste for the long period. Thus the formation of titanate of strontium, which is one of the fission products, with emphasis on chemical reactivity of starting materials, was studied by use of thermogravimetry and X-ray diffraction method. Starting materials used were nitrate, carbonate and hydroxide, and also salts of organic acids as format, acetate and oxalate of strontium, and hydrate, anatase and rutile of titanium dioxide. The chemical reactivity of the reagents was compared with each other using initial temperatures of the reaction on TG curves and conversion to strontium titanate. The products were mainly the monotitanate in all reaction systems. Formate, acetate and oxalate of strontium were converted to carbonate in air or in helium before the salts reacted with titanium dioxide. The order of the chemical reactivity of strontium salts was：hydroxide > nitrate > carbonate and that for titanium dioxide was：anatase > hydrate≒rutile