The aim of this programme is to undertake fundamental research that will advance our understanding of the potential effects that the introduction of a Geological Disposal Facility (GDF) for radioactive waste might have on lower strength sedimentary host rock. This includes detailed conceptualisation of the geology and groundwater.
The UK has generated electricity from nuclear power for more than 60 years, and the use of nuclear power is set to persist and scale up as part of the UK government’s plan to reach net zero carbon emissions by 2050.
To deliver to these objectives there is a need to both invest in new capability as well as to have a clear plan for disposal of the generated nuclear waste in a way that is not harmful to the environment or human health.
The development of a Geological Disposal Facility (GDF) is central to government policy regarding the management of higher activity radioactive wastes.
Lower strength sedimentary rocks (LSSR) are one of the geological environments identified as being potentially suitable for providing a host rock in which to construct a GDF. However, there are fundamental knowledge gaps around the geology, hydrogeology and controls on subsurface properties of these systems. These gaps must be addressed to provide the fundamental underpinning knowledge required to inform future decisions around disposal of radioactive waste in the UK it transitions to low carbon energy production.
This programme will address the following objectives to understand and predict how potential lower strength sedimentary host rock environments might be impacted by the introduction of a GDF.
Objective 1: geological isolation challenges
The effective, long-term isolation of radioactive waste requires a detailed knowledge of the physiochemical nature of the larger rock volume within which the waste will be disposed. The resilience of the rock volume to perturbations in stress, chemistry and temperature, induced by subsurface engineering, waste emplacement, and GDF closure, also needs to be understood.
This objective focuses on characterisation and conceptualisation of geological complexity and heterogeneity at multiple length and time scales within lower strength sedimentary rocks, addressing key knowledge gaps such as:
- uncertainty around the likely variation in values describing the magnitude and evolution of flow and geomechanical properties in LSSR formations in the UK (for example with varying lithology and heterogeneity)
- identification of key processes (for example, advection versus diffusion in the matrix, or transmissivity in the undisturbed far field or excavated damage zone) and how they will evolve over the lifetime of the repository
Objective 2: contaminant pathways
The aim of this objective is to develop a mechanistic understanding of retention or transport within lower strength sedimentary rocks, for:
- priority radionuclides (for example, uranium and uranium series radionuclides)
- longer-lived fission products and non-radioactive contaminants (for example, organics and heavy metals)
To increase understanding of the key controls on radionuclide transport processes in evolving LSSR systems, this objective focuses on radionuclide and, or contaminant behaviour, including:
- radionuclide interactions within relevant LSSR host rock materials
- groundwater geochemistry
Objective 3: mathematical modelling
The programme aims to develop system level mathematical models of key sedimentary systems, using the baseline information developed through objectives 1 and 2.
The mathematical models and codes developed as part of this research programme will focus on several key processes that would affect the environment surrounding a GDF, for example:
- thermal effects from waste and damage caused by excavation process
- fracture network development and consequent effects on water and gas flow and transport properties
- deformation processes within the host rock and the overall geochemical evolution of the system
Additionally, this objective will seek to take new approaches to computational modelling, by:
- building fully coupled thermo-hydro-mechanical-chemical computational codes that can accurately model the growth and coalescence of fracture networks in LSSR
- validating these codes against relevant analytical solutions and data generated in objectives 1 and 2 of the programme
This programme is independent from other Nuclear Waste Services (NWS) investments and work concerning siting of a GDF within the UK, and research conducted and funded by this programme will not form the appraisal of any specific site.