Characterisation of Synroc microstructure and durability and its influence on final disposal

Principal phases in Synroc C have been identified as zirconolite, zirkelite, polymignyte, perovskite and the hollandite, pyrochlore and magnetoplumbite structure types. Intermetallic alloy phases are also present. Investigation has established that Synroc C, like all multiphase ceramics, contains intergranular films, usually less than 30 angstrom wide. Detailed microstructural and surface analytical studies of leached Synroc C under hydrothermal conditions have revealed the alteration of the chemical environments of the different major phase elements and also of the high level waste elements. Changes in the composition of the surface have also been monitored in leached Synroc C. Mechanisms for the leaching and dissolution of Synroc are proposed. (orig./PW)