Key Topic 2: Wasteforms and their Behaviour


This research area deals with understanding the behaviour of various wastes in geological repositories.  All wastes that may require geological disposal are within the scope of this research area, thus including the waste categories of spent uranium oxide (UO2) and mixed oxide (MOX) fuels, vitrified high-level waste (HLW), long-lived intermediate level wastes (ILW) and some low-level wastes (LLW).  Spent fuel from research reactors and legacy wastes are also considered.  The wastes represent the potential source terms for release of radionuclides if and when waste containers are breached.


The purpose of the research within this research area is to understand safety-relevant processes, in particular the contribution of the wasteform to radionuclide retention in the repository.  It is important to systematically define the physico-chemical properties of the waste materials, including their chemotoxic properties and presence of complexing agents, as well as the total inventory of various radionuclides – these properties together determine the time-dependent release of radionuclides.  Methods for quantification of difficult-to-measure radionuclides are required here.  This allows the formulation of mathematical models in order to assess radionuclide release from a repository.  Spent nuclear fuel, when considered as the waste form for direct disposal, needs to be well characterised to address both pre-disposal and post-disposal issues.  This characterisation is central for heat-output calculations and criticality safety analyses, which impact optimisation of repository plans and component requirements, and the definition of the initial state for the assessment of post-closure safety.    Continued studies concerning how processes expected in the repository will affect the release rate of radionuclides from the spent fuel is required for both uranium oxide and MOX fuels.  Understanding the waste source term directly relates to the first pillar of the IGD-TP’s Vision 2040, to “safely operate” disposal facilities, and also to the ability to optimise the design and operation of the repository (the second pillar, “optimise and industrialise”).