Radiation effects in Thorium Phosphate Diphosphate Th4(PO4)4P2O7. A theoretical approach

Abstract

ABSTRACTThorium phosphate diphosphate Th4(PO4)4P2O7 (β-TPD) was already proposed for plutonium and minor actinides immobilization. Synthesis of Th4-xPux(PO4)4P2O7 with x∼1.5 corresponding to roughly 26 wt % of Pu was achieved demonstrating the thermodynamic stability of this phosphate-based material even for high plutonium mole loadings. We established reliable inter-atomic potentials in the shell-model approach for the β-TPD in order to calculate the Frenkel defects formation energies as well as the threshold displacement energies. Furthermore we carried out a detailed analysis of the energetic pathways for the corresponding Frenkel defects annealing. We deduced that the diphosphate sub-lattices may be easily displaced while the annealing mechanisms are revealed to be complex requiring highly energetic pathways, thus constituting the main defects configurations that may lead to the amorphous state.