SYNTHESIS AND CHARACTERIZATION OF ZEOLITE-BASED CERAMIC MATRICES FOR FIXATION OF IODINE

Preparation of ceramic materials for fixation of radioiodine is studie d. Two matrices based on NaX and Cu-zeolites are proposed, allowing pr eparation of ceramics with various phase compositions. In the first ca se, the ceramics composition approximately corresponds to a mixture of feldspar and I-containing sodalite and in the second case, to a mixtu re of quartz, corundum, CuI, and (when Cu-zeolite-2 with high sodium a nd sulfur contents is used) I-containing sodalite. The resulting I-con taining ceramics is sufficiently resistant against leaching. After a 3 6-day holding under conditions of the MCC-1 test, the rate of iodine l eaching was 0.9 g m(-2) day(-1) for the best samples, which is 4-5 tim es lower than that from sodalite matrices and cement and bituminous co mpounds based on poorly soluble iodine compounds but by two orders of magnitude higher than for compositions based on epoxy resin and lead i odide. The rates of leaching of iodine from the zeolite-based ceramics are comparable with those of alkali and alkaline-earth metals from bo rosilicate glasses. The trend to decreasing rates and degree of leachi ng allows a conclusion that the subsequent degree of leaching of iodin e from these samples will be no more than 0.5%, permitting a long-term storage of iodine radionuclides in such ceramic matrix. The proposed method for immobilization of radioiodine in ceramic matrices has certa in advantages: the resulting material is sufficiently stable; the meth od provides a considerable reduction of the volume of wastes; and, las t but not least, the ceramics is prepared from commercial zeolites cap able of absorbing iodine directly from off-gases of fuel reprocessing plants. These ceramic materials (especially based on feldspare/sodalit e compositions) are compatible with natural rocks (syenites) in accord ance with the rule of phase and chemical conformity in the matrix-coun try rock system, In this respect the ceramics outperforms the present matrices for fixation of iodine (Ag-zeolites, epoxy resin-based compou nds, etc.).