Long-term behaviour of TRU-waste-bearing ceramics Task 3 Characterization of radioactive waste forms a series of final reports (1985-89) No 16

The aluminium-silicate ceramic matrix KAB 78, developed for the Immobilization of TRU wastes, has been doped with 20 wt% of Pu(238)O2, in order to irradiate the matrix by the same α-dose over a period of three years, as accumulated within a storage time of about 100 000 years, when loaded with the real TRU waste. The Pu(238)-doped ceramic KAB 78 was investigated, by means of ceramographic methods, while the accumulated α-dose increased up to 8.33 E 9 Gy (9.4 E 18 α-decays/g). 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 α-dose. The lattice constants of the matrix phases corundum and mullite were found to be only slightly enlarged. Any sign of metamictization beginning has not been detected. Changes in the micro-structure have not occurred and the amount of stored energy has been determined to be less than 11 J/g. In order to study the corrosion behaviour of the Pu(238)-doped ceramic and ceramics loaded with real dissolver residues, leach tests were performed over a period of 214 days, using either Q-brine or Dl-water of up to 2000C. Leach rates, based on the total α-activity were found to be slightly higher, when leaching the Pu(238)-doped ceramics. Reaction zones of 150 up to 600 μm thickness were formed, with a significant decrease of Si, whereas the concentrations of Al and Pu remained unaffected