Alpha-Recoil Damage in Monazite: Preferential Dissolution of the Radiogenic Actinide Isotopes

A preferential dissolution by a factor of 1.1 to ~10 of the radiogenic nuclides 234U, 230Th, and 228Th relative to their corresponding structurally incorporated isotopes 238U and 232Th has been observed upon leaching of natural monazite samples in a bicarbonate-carbonate solution. This isotopic fractionation may be attributed to radiation damage caused by alpha-recoil atoms. The observations have implications for the storage of crystalline nuclear waste forms in deep geological formations. The damage may endanger the integrity of any crystalline phase that contains alpha-emitting nuclides in groundwater environments. It is inferred that in monazite-like phases the overall alpha-recoil damage may increase nearly in proportion to the alpha-particle dose over the long time range (~105 yr) required for the isolation of actinide wastes.