Fundamental research on thermal plasma technology for treatment of low level radioactive solid waste

It is expected to establish the technology for treatment of low level radioactive solid waste generated in nuclear power plants. The main problems are volume reduction and stabilization of radionuclides acceptable for final disposal. Thermal plasma technology offers advantages for such waste treatment because of the easy supply of heat at high temperature independent on chemical and physical properties of the waste. New, non-contaminated waste, such as metallic, inorganic and combustible materials, have been melted in a crucible furnace. Transferred type of a DC plasma torch with a solid electrode was used as heat source and rated up to 50 kW. The main results obtained are as follows: (1) Metallic and inorganic materials can be melted and vitrified. Combustible materials can be pyrolyzed. Consequently high volume reduction rates can be attained. (2) Compressive strength of solidified products is more than twice as great as that of cement composites used for solidification of the liquid waste. Leaching rate of main components of the slag layer is in the same order of that of the high level radioactive waste glass. (3) In order to get guiding principle for design of off-gas treating system, compositions of the off-gas and properties of the dust entrained in the off-gas are clarified. From these results, technical prospects so that plasma heating technology can be applied for treatment of low level radioactive solid waste have been obtained. (author)