Towards Safe Geological Disposal of Radioactive Waste in Lower-Strength Sedimentary Rocks (GEOSAFE).

The UK has been generating electricity from nuclear power for over sixty years. Nuclear power generates 15% of the UK's electricity as of 2023, and current government plans call for this percentage to rise to about 25% by 2050. Consequently, the issue of safely disposing of the UK's existing stockpile of radioactive waste, as well as any waste that may be generated in the future, is clearly posed. Current UK government policy is to dispose of the higher activity wastes in an underground geologic disposal facility, known as a GDF. Construction of such a facility will have an estimated cost of £20-53 billion, over a period of several decades. The purpose of a GDF is the safe disposal of radioactive waste for periods of tens of thousands of years, in a manner that ensures that any leakage of radioactive materials into the surrounding biosphere is kept below specified limits. One of the rock types that has been identified as a potentially suitable host rock for the location of a GDF are lower-strength sedimentary rocks, known as LSSRs. Siting and construction of a GDF in LSSR will require the development of a quantitative understanding of the physical and biogeochemical properties of the host rocks surrounding the GDF. However, many fundamental gaps still exist in our knowledge of the issues related to performance of these host rocks as a geological barrier to radionuclide transport. In their call "Derisking geological disposal of radioactive waste in the UK", NERC have grouped these knowledge gaps into three Challenge Areas: geological isolation of the waste, potential contaminant pathways for radioactivity to escape into the biosphere, and new advances in mathematical modelling of the relevant processes. To address these Challenges, we have assembled a multidisciplinary consortium composed of over twenty scientists at seven UK universities and research institutes, many of whom have extensive experience and expertise in various areas related to radioactive waste disposal, and/or in closely related areas of subsurface science and engineering. In addition to these investigators, seven PhD students will be funded by the participating institutions, to further support the objectives of this project. As the ultimate goal of this work is the safe geological disposal of radioactive waste, we have named our project "GeoSafe". The GeoSafe research consortium will carry out innovative research that will investigate fundamental behaviour of LSSRs in the context of the three Challenges. We will measure mechanical, flow, and transport properties of LSSR rocks over a range of scales, with an emphasis on quantifying the effects of heterogeneities such as sedimentary architecture, bedding, laminations, inclusions, and fractures. We will use cutting edge multi-scale imaging techniques, and novel experimental techniques for coupled measurements, that will reconstruct properties of the rocks of interest across scales. We will investigate the effects that chemical and biological changes in LSSR rocks will have on the rock's permeability and dispersivity, conducting novel radionuclide diffusion and advection experiments paired with dynamic multi-scale imaging. GeoSafe will investigate the effects of possible existing fractures, quantifying whether these are likely to seal, and what their effect on transport may be if they remain open. Numerical simulations will be performed to assess flow and transport of liquid and gas flowing fluids, and as well as reactive radionuclide transport, within the vicinity and in the surrounding region of the GDF. Taken as a whole, GeoSafe will produce and synthesise a unique set of data, and develop state of the art experimental and computational tools and methods, that will be essential in understanding the fundamental behaviour of lower-strength sedimentary rocks in the context of evaluating the performance of a UK Geological Disposal Facility.