Evaluation of the technical feasibility of new conditioning matrices for long-lived radionuclides

Several matrices have been selected for the conditioning of long-lived radioactive wastes: a compound made of a iodo-apatite core coated with a densified matrice of vanadium-phosphorus-lead apatite for iodine; the hollandite ceramic for cesium; the britholite, zirconolite, thorium phosphate diphosphate, and the monazite-brabantite solid solution for minor actinides; and a Nb-based metal alloy and phosphate or titanate-type ceramics for technetium. This report presents the results of the researches carried out between 2002-2004 during the technical feasibility step. The main points described are: - the behaviour of matrices under irradiation. These studies were performed thanks to an approach combining the characterization of natural analogues, the doping of matrices with short-lived radionuclides and the use of external irradiations; - the behaviour of these matrices with respect to water alteration; - the sensibility of these structures with respect to the incorporation of chemical impurities; - a package-process approach including the optimization of the process and preliminary studies about the package concept retained. These studies show that important work remains to be done to develop conditioning matrices suitable for iodine and technetium, while for cesium and minor actinides, the first steps of the technical feasibility are made. However, it remains impossible today to determine the structure having the best global behaviour. (J.S.)