Irradiation effects on thorium phosphate diphosphate: Chemical durability and thermodynamic study

Since thorium phosphate diphosphate (β-TPD) can be considered as a potential host specific matrix for the long-term storage of actinides in the field of an underground repository, it is necessary to study the irradiation effects on the chemical durability of this material. In this aim, leaching tests were realized on pre-irradiated thorium–uranium phosphate diphosphate (β-TUPD) samples. The evolution of the normalized leaching showed that thorium often precipitates as a neoformed phosphate-based solid onto the surface of the leached samples while uranium (IV) is released in the leachate consequently to its oxidation into the uranyl form. The pre-irradiation accelerates the formation of the neoformed phase. On the contrary, the characterization of the neoformed phase through various techniques (EPMA, XRD, μ-Raman) showed that the pre-irradiation has no effect on the thermodynamics equilibria occurring onto the surface of the samples.