Nuclear Waste Glasses: Recent Advances in the Spectroscopic Investigation of Their Structure

Abstract

High- and intermediate level, long-lived wastes (class I and II wastes: IAEA 1981) result from the irradiation of the nuclear fuel within a reactor and its subsequent reprocessing. They include the fission products, actinides, and heavy elements formed in the fuel by neutron capture and radioactive decay reactions. The largest volumes are produced during spent fuel reprocessing and contain only about 0.1% of the uranium and 1% of the plutonium (Roxburgh 1987) and are referred to as high-level wastes (HLW). HLW need to be contained in an environment providing an efficient shielding and isolation from biosphere as well as an efficient dissipation of the heat generated by the radioactive decay of the waste. At present, most HLW are stored in liquid cooling tanks, though they are not thought to provide a long-term solution to the disposal of high-level nuclear waste. The long term disposal option remains deep geological burial, isolating the waste from the biosphere for the requisite periods of time, mostly by preventing from transportation by groundwater. Among the main technical requirements of solidified HLW are low leachability, high chemical, thermal, and mechanical stability as well as industrial feasability. A large number of solid waste forms meet these criteria, and they include glasses, cements, and synthetic rocks. Nuclear waste glasses of borosilicate composition are now developed at an industrial scale (Sombret 1985) and we will survey below some recent findings concerning their structure.