Suvorova V.A., Kotelnikov A.R., Akhmedzhanova G.M. Synthesis of ceramic phosphate-containing matrices for immobilization of REE (La, Ce) radionuclides.

The aim of the work has been binding of REE (La,Ce) radionuclides, contained in nuclear fuel waste, in ceramic matrix materials by synthesizing them from phosphates, imitators of the corresponding elements, and available raw material, i.e. natural rocks.

Synthesis enables one to obtain a cheap end product that meets the principles of (1) multibarrier character of protective compositions and (2) phase and chemical compatibility in the system matrix-host rock. The produced multibarrier protective compositions consist of monazites and alumosilicates each of which is a barrier against the escape of radionuclides, through binding them chemically or mechanically, the third barrier will be lost rocks with which the synthesized ceramics is in phase and chemical compatibility (equilibrium).

The silicate components and phosphates were crushed in an agate mortar for 1.5 h until they became homogeneous in composition. 1.5 g pellets 5-6 mm in height and 8 mm in diameter were produced from the mixtures by cold compacting under a pressure of about 100 kg/cm2 at room temperature. The produced pellets were sintered in platinum crucibles for 3 days in an electric heater 'KO-14' at 1180oC.

The produced ceramic specimens had the composition corresponding to natural granite and tuff with an admixture of REE phosphates.

The leaching data obtained phosphate-silicate ceramic matrices demonstrated their high stability. After a 50-day duration under the MCC-1 test for the specimens on the base of granite the leaching rate of Ce was 2.78∙10-3 g/m2∙day, and that of La 8.24∙10-3g/m2∙day, which is comparable with elements leaching rates from synrock.