Ion implantation effects in insulators and the long-term stability of radioactive waste storage materials

Abstract

Most insulator materials so far proposed for storing high-level radioactive wastes, such as glass and and the constituent minerals of ceramics are nuclear track detectors. Lead ion implantation experiments show that such materials should be transformed into “giant” nuclear tracks, when the internal fluence of heavy recoils emitted during the α-decay of actinide elements stored in them exceeds a critical value, which corresponds to an equivalent storage period of a few thousand years for the wastes expected from a pressurized water reactor. In contrast, actinide bearing minerals are much more stable against α-recoil damage. As nuclear tracks are extremely chemical reactive, α-recoil damage is expected to shorten the lifetime of storage materials such as glass and ceramics against dissolution in ground waters. Fortunately new nuclear track concepts are already yielding guidelines for predicting and improving the long-term stability of storage materials. The results of the present studies also bear on the physics of ion implantation phenomena an insulator targets exposed to high fluences of low energy ions.