Structural recovery of self-irradiated natural and Pu-doped zircon in an acidic solution at 175 °C

We have investigated the aqueous stability of self-irradiated natural and synthetic ²³⁸Pu-doped zircon (4.7 wt% of ²³⁸Pu) in an acidic solution at 175 °C. Both zircon samples have suffered a similar degree of self-irradiation damage, as given by their degree of amorphization. X-ray diffraction measurements revealed that during the hydrothermal treatment only the disordered crystalline remnants recovered in the natural zircon, whereas in the ²³⁸Pu-doped zircon the amorphous phase strongly recrystallized. Such a different alteration behavior of natural and Pu-doped zircon is discussed in terms of two fundamentally different alteration mechanisms. Our results demonstrate that further experimental studies with Pu-doped zircon are required before any reliable prediction about the long-term aqueous stability of an actinide waste form based on zircon can be made.