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2021

Valentin JOLIVET - 27th January

"Incorporation of iodine in nuclear glasses by vitrification under high pressure"

129I is a product of the fission of uranium in nuclear power plants. It is radiotoxic, very mobile in the environment, and has a long half-life (15.6 Ma). The conditioning of 129I in nuclear glasses for geological storage is complicated by its high volatility at high temperature. The vitrification of nuclear glasses under pressure is a solution that can overcome this problem, because the solubility of volatile elements in liquids increases with pressure. Nuclear glass analogues have been vitrified under high pressure (0.5-2 GPa) to determine the solubility of iodine in glasses, as a function of thermodynamic and compositional parameters. The solubility of iodine in glasses depends on pressure, boron content, but also on the content of non-network forming cations. Polymerized borosilicate glasses such as ISG nuclear glass simulant incorporate ~1 mol.% iodine, while depolymerized glasses such as "Low Activity Waste Glass" incorporate ~2 mol.%. Iodine is incorporated into glasses in the vicinity of the non-network-forming cations. In doing so, it changes the polymerization state of the lattice. Iodine has a depolymerizing effect on polymerized glass, and vice versa for depolymerized glass. The solubility of iodine is also strongly influenced by its oxidation state, with I5+ being much more soluble in glass than I-.