Résumé
$\beta$-thorium phosphate diphosphate ceramic ($\beta$-TPD), $\beta$-Th4(PO4)4P2O7, was proposed as a potential actinide-bearing phase for nuclear waste storage. Self-irradiation by a-decays, due to the actinide loading, could affect the good intrinsic performances of this material. The evaluation of irradiation effects on the chemical durability of the ceramic is a crucial issue. Radiation effects were simulated by external ion beam irradiations. Under high-energy ion irradiation, amorphization was achieved above a critical threshold for electronic energy loss (Se = 5 MeV lm$\mu m^1$).Thermal annealing enables to fully recover the initial crystalline structure after heating for 15 h above 973 K. Amorphization appears thus completely reversible. The activation energy of annealing is equal to 2.8 eV. Ion beam induced amorphization and recrystallization by thermal annealing were found to be isotropic processes. Irradiations in the nuclear stopping regime lead to a complete amorphization of $\ beta$b-TPD at a critical dose of 0.2 dpa.