Résumé
In the field of the immobilization of high level activity and long life radwaste for a deep underground repository, several phosphate matrices were already proposed to delay the release of actinides to the biosphere. Among them, Thorium Phosphate-Diphosphate (TPD) and associated solid solutions were considered. In order to improve the homogeneity of the samples prepared, a new way of preparation based on the precipitation in closed containers, at 150°C, of the Thorium-Phosphate HydrogenPhosphate hydrate (TPHP) or associated Thorium – Uranium (IV) Phosphate HydrogenPhosphate hydrate (TUPHP) was developed. Well crystallized and single phase TUPD solid solutions of general formula Th4−x
U
x
P6O23 were prepared after heating above 950°C. Dense TUPD pellets were also obtained through a two-steps procedure involving a uniaxial pressing of the powder at room temperature then a heating treatment at 1250°C for 10 hours. Several properties of the pellets such as their chemical durability during leaching tests were considered carefully. All the normalized dissolution rates of powdered and sintered TUPD solid solutions remained low by comparison to that reported for several other ceramics studied in the same objective.