ALUMOSILICATE-BASED CERAMICS ARE SUITABLE MATRIX MATERIALS FOR THE IMMOBILIZATION OF TRU-WASTE. THE FEASSIBILITY OF THIS CONDITIONING METHOD HAS BEEN DEMONSTRATED BY SYNTHESIZING ALUMOSILICATE CERAMICS, LOADED WITH ORIGINAL TRU-WASTE UP TO 20 WT.-% ON LAB-SCALE. THE FINAL PRODUCTS CONSIST OF A MIXTURE OF MULLITE (AL6SI2O13) AND CORUNDUM (AL2O3), AS WELL AS ACTINIDE OXIDES AND FISSION PRODUCT ALLOYS AND OXIDES. THE LEACH RATES FOR ACTINIDES SHOW VALUES BETWEEN 10-8 AND 10-9 G/CM D AFTER THE ISO-DRAFT.
AIM OF THE CURRENT PROGRAMME IS TO GET INFORMATION ON THE LONG TIME BEHAVIOUR OF THESE KIND OF CERAMICS WITH RESPECT TO RADIATION AND HYDROLYTIC INFLUENCES.
CHANGES IN MICROSTRUCTURE AND HYDROLYTIC STABILITY AS A FUNCTION OF LONG STORAGE TIME, INDUCED BY HIGH ALPHA-DOSIS AND THUS ACCELERATING MUTUAL INTERACTIONS, WILL BE RECORDED.
THE GOAL OF THIS PROGRAMME IS ACHIEVED BY PERFORMING "TIME-LAPSE" EXPERIMENTS. THAT MEANS DOPING THE CERAMICS WITH A SHORT-LIVING ALPHA-EMITTING RADIONUCLIDE, SO THE DESIRED HIGH ALPHA-DOSE IS TRANSMITTED TO THE MATRIX WITHIN SHORT TIMES.
The aluminium silicate ceramic matrix KAB 78, developed for the immobilisation of radioactive wastes, has been doped with 20% of 238-plutonium dioxide, in order to irradiate the matrix by the same gamma-dose, over a period of 3 years, as accumulated within a storage time of about 100,000 years, when loaded with real radioactive waste. The plutonium-238 doped ceramic KAB 78 was investigated, by means of ceramographic methods, while the accumulated gamma-dose increased up to 8.33E9 Gy.
Special attention was directed to the development of the microstructure, the crystalline state and the lattice constants of the matrix phases, as well as to stored energy, as a function of the accumulated gamma-dose.
In order to study the corrosion behaviour of the plutonium-238 doped ceramic, and ceramics loaded with real dissolver residues, leach tests were performed.
B1. SYNTHESIS OF SAMPLES :
- CERAMICS (TYPE KAB 78), LOADED WITH 30 WT.-% OF DISSOLVER RESIDUES.
- CERAMICS (TYPE KAB 78), LOADED WITH 20WT.-% OF PU(238)O2.
B1.1. PREPARATION OF THESE SAMPLES FOR CERAMOGRAPHIC AND LEACHING INVESTIGATIONS.
B2. CHARACTERIZATION OF THESE SAMPLES AS A FUNCTION OF TIME (ALPHA-DOSIS).
B3. LEACHING OF THESE SAMPLES AT ELEVATED TEMPERATURE IN Q-BRINE.
B4. CHARACTERIZATION OF THESE SAMPLES AFTER THE LEACHING EXPERIMENTS AND AFTER REACHING THE ALPHA DOSIS REQUIRED.