PhD Studentship - Coupled Thermal-Hydro-Mechanical and Chemical (THMC) Processes in Salt Formations for Disposal and Storage Applications

This PhD position has agreed funding jointly by the National Nuclear Laboratory and Department of Chemical Engineering of the University of Manchester. This is a full scholarship which will cover tuition fees for UK-based students and provide an annual stipend in line with EPSRC recommended levels (£19,237 for 2024/25) for the 42 months duration of the project. The successful applicant will be expected to start in Sept 2024. This scholarship is available only to UK students eligible for home fee status.

Objective: This PhD project aims to: 1) improve the conceptual understanding of the physicochemical processes and mechanisms that govern the migration of gases and brine in rock salt formations under the influence of a thermal gradient; 2) Develop a novel and efficient THMC numerical framework that will be validated against experimental data collected by international research programmes.

Background:

One potential host rock for a Geological Disposal Facility (GDF) is fine-grained sedimentary rock or mudstone – in the terminology of a GDF, this is a lower-strength sedimentary rock (LSSR) geological setting. LSSRs are considered potentially suitable host rocks due to their very low permeability and ductile nature which can lead to seal healing of faults and fractures under burial conditions. No decision has been taken upon where, or in which geology, a GDF will be sited, but the volunteer process underway at the moment means that one host rock under consideration is the highly complex and heterogeneous Triassic aged Mercia Mudstone Group (MMG).

To satisfy the requirements for a GDF safety case, many near-field and far-field factors need to be taken into account, including, for instance, the likelihood that fluid and solutes could flow or diffuse from the waste into the surrounding host rock and impact the far-field (particularly receptors within the biosphere).  The assumption is that LSSRs, by their very low permeability, will mean such transport is limited. However, currently, multi-scale (nano-scale to kilometre-scale) assessment and modelling of potential pathways have not been carried out for the MMG. Such analysis is challenging due to the small scale of 3D pore networks and micro-fractures in LSSR rocks. This PhD research will utilise state-of-the-art multi-scale imaging techniques at the University of Manchester to better quantify and understand these 3D characteristics at multiple scales, and to upscale to the large scale appropriate to the far-field of a GDF.

Key questions:

• How do 2D and 3D nano- and micro-structure vary within key units within the Mercia Mudstone Group?
• How can cm- to metre-scale variability in heterogeneity be upscaled to the km-scale so that far-field aspects of a GDF be understood?
• Can 3D image-based data be used to construct fluid reactive transport models applicable to the short, medium and long-term behaviour of the MMG as a host rock for a GDF?

Tasks:

• The development and implementation of mathematical models that capture these coupled processes phenomena.
• The validation of the numerical models against experimental data.

Impact:

This project will develop novel mathematical models to quantify the long-term thermal-hydraulic-mechanical and chemical evolution of MMG’s evaporitic strata. The output of this work will support the safety assessment for rock salt disposal of radioactive waste.

Please contact the main supervisor, Dr. Masoud Babaei before you apply: (masoud.babaei@manchester.ac.uk)

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