Performance of aged cement grouts for encapsulating radioactive wastes

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The overarching aim of this PhD project is to develop a deep understanding of the chemical, microstructural and physical changes that occur due to long-term interactions between NRVB and wasteform grouts under repository relevant conditions. We will achieve this via a novel approach that combines thermodynamic modelling with quantitative microstructural analysis and mass transport characterisation. This will produce a rich dataset that will complement and extend the work from previous studies. Ultimately, the new knowledge generated will inform and strengthen the post-closure safety case of the UK Geological Disposal Facility.The research will be carried out within the Imperial Centre for Infrastructure Materials with PhD training provided by the EPSRC CDT in Nuclear Energy Futures. The research consists of three interconnected technical work packages that will apply a range of advanced modelling and experimental characterisation techniques. We will use thermodynamic modelling [2, 3] to obtain a complete chemical understanding of the NRVB-grout systems up to ten years of ageing, and determine their long-term chemistry and indicative physical properties (e.g. porosity) at ageing times of 100s years and beyond. We will also perform quantitative microscopy [4], pore structure/solution characterisation and micromechanical studies at the bulk and interface regions. This will provide comprehensive understanding of microstructural gradients (pore structure, microcracking), solid phase assemblage, micromechanical properties and pore solution chemistry. Finally, we will evaluate the integrity of the cement grouts by measuring their resistance to mass transport (permeation, diffusion, absorption, conductivity) in fully saturated and partially saturated conditions [5]. The microstructural data will be used to complement thermodynamic modelling and mass transport properties to form predictive relationships. This will allow us to assess the effects of long-term hydrothermal storage on the barrier performance of wasteform grout-backfill systems.