Role of vitrification in radioactive waste management

Miura, Nobuyuki

Borosilicate glass is used for solidification of high-level radioactive wastes. Glass ceramics so far have been studied for improving the properties and reliability of the solidified materials as an alternative matrix, but vitrification has been selected as the most suitable method from the viewpoint of the feasibility of the manufacturing process. The main component of radioactive waste is fission products from the reprocessing on the spent fuel of the nuclear power plants. Fission products are consisted from isotopes of 30 or more elements and are strong / emitters. It also contains strong a-emitters such as americium. These are metal elements, which react with the raw glass cullet and are stably confined in the vitrified solid by cooling and solidification. Improvement of the melting technology is being continued. In recent years, Japanese waste vitrification researchers have been conducting the investigation on feasible technologies not only for high-level liquid wastes but also for low-level liquid waste generated from the operation or decontamination of nuclear power plants etc. For the secondary wastes of water treatment at the Fukushima Daiichi Nuclear Power Station Accident, the examinations of the volume reduction and its stabilization methods are in progress. Since glass has quite low water solubility, generation of hydrogen gas which is often observed in other matrices can be ignored. Even for the solidification of low level waste, glass can greatly contribute to the reduction of this risk.