Solubility of simulated high-level radioactive wastes in CaO-stabilized zirconia

The reaction between simulated high-level radioactive wastes (HLW) and CaO-stabilized zirconia with CaF2 structure has been studied in the temperature range of 800--1,5000C in air and in a mixture of 4%H2+96%He. Under the heat treatment in air at temperatures between 1,000 and 1,4000C, 4w/0 simulated HLW was dissolved in the CaF2 phase. The lattice parameter of the CaF2 lattice increased with HLW content according to the equation a= 0.5134+0.00028x nm, where x is the HLW content in w/0. In the region of 4--20w/0 HLW, two phases were present: the CaF2 and scheelite type phases. The actinide and rare earth elements were dissolved in the CaF2 lattice, of which lattice parameter varied with HLW content in the form a=0.5141+0.00014x nm. Under the heat treatment in a mixture of 4%H2+96%He, three phases were formed in the sample containing the HLW. They were the CaF2 phase, (Sr, Ca) ZrO3 with orthorhombic structure and Mo metal. The actinide and rare earth elements were fixed in the CaF2 lattice. The increase of the lattice parameter of the CaF2 lattice was given by the expression a=0.5134+0.00022x nm. (author)