Impermeable Graphite: A New Development for Embedding Radioactive Waste

Abstract

The natural occurrence of graphite proves its geological stability over long time periods and therefore it could be considered as a matrix for embedding radioactive waste. However its porous structure affects the possible use of graphite as long term stable waste matrix for final disposal. Aqueous phases can penetrate the pore system and radionuclides adsorbed on the surface can be leached. Furthermore slow corrosion in aquatic phases can be induced by high irradiation dose rates in the range of 10−5 to 10−7 gm−2d−1. Therefore radiation induced corrosion process cannot be neglected in geological time scales. These problems can be solved with a graphite material with a closed pore system. A graphite composite material with an inorganic binder has been developed with a density > 99.7% of theoretical density and a negligible porosity. An initial calculation predicts that the life time of the graphite will be at least 2 orders of magnitude higher than porous graphite. This material represents a long term stable leaching resistant matrix applicable for the embedding of irradiated graphite (i-graphite). Natural graphite can be added to improve the compaction behavior and mechanical properties. Additional applications could be the embedding of other radioactive wastes in this matrix.