Consequences of the ion beam irradiation on the chemical durability of thorium phosphate diphosphate – kinetics study

In the field of the long-term specific immobilization of actinides, thorium phosphate diphosphate (β-TPD), as potential candidate, must respond to several criteria. Among them, the material must present a good resistance to irradiation and keep its initial good properties such as resistance to aqueous alteration. In order to check this later point, sintered samples of β-TUPD solid solutions were pre-irradiated with ion beams with various conditions (fluence, stopping power) then submitted to leaching tests in different media (pH, temperature, complexing reagents, flow rate, ...). The normalized dissolution rates depend significantly on the amorphous fraction (increase by a factor of 10–100 between unirradiated and fully amorphized materials). On the contrary, the pre-irradiation of the samples does not affect the kinetic parameters of the dissolution such as the partial order relative to the proton concentration (n = 0.37 ± 0.01 and n = 0.34 ± 0.01 for unirradiated and fully amorphized samples, respectively) and the activation energy of the reaction of dissolution (Eapp = 49 ± 4 kJ mol−1 and Eapp = 42 ± 4 kJ mol−1 for unirradiated and partly amorphized samples (fA < 1), respectively).