Abstract:
Structural damage to actinide-bearing matrices upon their irradiation with Kr and Xe ions with energies of 1.0 and 1.5 MeV was studied. Actinides are incorporated into oxides with fluorite-type structures (zirconolite, pyrochlore, and murataite), uranium titanate (brannerite), silicates and ferrites with a garnet lattice, and a (Ca, REE) silicate with an apatite structure (britholite). The radiation doses for complete structural amorphization at 25°C were as follows (in units of 1014 ions/cm2): 2.9 for zirconolite, 1.8-2.4 for pyrochlore, 1.5-2 for garnet, 1.7-1.9 for murataite, 1.4 for brannerite, and 0.4 for britholite. The radiation resistance of phases expressed as the number of displacements per atom (dpa) ranges from 0.1 to 0.4 dpa. According to these data, a phase containing 10 Wt % 239Pu will be completely amorphized over 500-2000 yr. This will increase actinide leaching from the matrix by tens of times. Amorphization doses are several times higher for natural analogues because of healing of radiation damage to the mineral structure with time. Disposal of highly radioactive waste matrices in deep-well repositories with an elevated temperature of ambient rocks favors an increase in the resistance of the crystal structure to radiation and maintains the immobilizing properties of radionuclide-bearing matrices over longer periods.
