Failure mechanisms of high level nuclear waste forms in storage and geological disposal conditions

A schematic description of the main aspects constituting the back-end of the nuclear fuel cycle is provided: concepts and stages available or envisaged for the treatment of spent fuel, and main radionuclides (transuranics, fission and activation products) determining the properties of the waste form relevant for the storage/disposal concepts are mentioned. Nuclear fission determines the inventory, and, together with the irradiation conditions/history, the physical and chemical state of spent fuel at discharge. Radioactive decay determines the changes occurring after discharge; in particular, alpha-decay governs the accumulation of defects and damage in the waste; it produces also helium, whose accumulation behaviour over long time periods has to be assessed. The evolution of properties as a function of time is described in terms of mechanical stability and evolution of solid state properties; the main features characterizing the corrosion behaviour of high level waste are also described, including source term, radiolysis effects and chemical reactions occurring at the interface waste/waterJRC.E.2-Hot cell