Radioactive wastes vitrification

Borosilicate glass is capable to solidify the liquid wastes and to confine the radionuclides present in fission product solutions, not by coating, but thanks to the existence of chemical bonds with the glass oxides. Glass materials have a large chemical flexibility in comparison with crystal structures. In parallel to the studies of nuclear glass formulation, a continuous vitrification process has been developed in France which allows to generate glass in a highly radioactive environment. The first demonstration of the feasibility of this process was done at Marcoule in 1969 with the vitrification pilot system PIVER. The industrial vitrification facility of Marcoule started in 1978 for the confinement of spent fuel reprocessing wastes. This process was implemented at the R7 and T7 facilities of La Hague in 1989 and 1992, respectively. The process used today at La Hague comprises two steps: a calcination of fission products liquid solutions at 400 deg. C and a melting at 1100 deg. C in a crucible heated by magnetic induction. The molten mixture of glass and fission products is cast and solidified in 400 kg containers. Other vitrification processes have been developed like the cold crucible vitrification process and the vitrification in electrode heated ceramic melter. This article presents: 1 - the formulation of nuclear glasses: constraints, choice of vitreous systems, chemical reactivity between the waste and the vitrification catalyst, some basic properties of nuclear glasses, confining properties, perspectives of evolution of glass compositions; 2 - vitrification processes: vitrification with induction-heated metal crucible, with cold crucible, with electrode-heated ceramic melters; 3 - conclusion. (J.S.)