University of Leeds

In-situ disposal of cementitious wastes at UK nuclear sites

Deadline: Open all year round

Project Description

This fully funded UK Nuclear Decommissioning Authority (NDA) PhD bursary provides an exciting opportunity to pursue postgraduate research relating to waste management during the decommissioning of UK nuclear sites. The successful candidate will develop skills in waste characterisation using methods from geochemistry, environmental mineralogy and radiochemistry, utilising state of the art synchrotron and electron microscopy-based analysis. These skills are highly in demand by employers and the studentship will offer excellent springboard for a career in the UK Nuclear industry.

The reuse of construction and demolition wastes at nuclear sites as a bulk material supports the UK waste strategy by avoiding costly and environmental disadvantageous off-site disposal. The project is focused on understanding the interactions of real crushed concrete wastes produced at NDA sites and longer-lived radionuclide contaminants. Specifically, the PhD will use batch and flow through column experiments to understand the potential for reactive alkaline phases (e.g. calcium-silicate-hydrate, portlandite) in the waste to enhance radionuclide sorption; and, for carbonation reactions with dissolved and atmospheric CO 2 to produce secondary minerals (e.g. calcite), which can readily incorporate and immobilise important radionuclide contaminants (e.g. Sr-90; U). The PhD will investigate the fate of radionuclides incorporated in, or transported into a crushed concrete waste disposal site, and the impact of leachate from aged and freshly crushed materials on the stability of radionuclides in neighbouring contaminated ground. The work will help determine if in situ disposals can meet strict regulatory standards, and, if other associated benefits such as radionuclide attenuation and CO 2 capture can be realised in Nuclear Decommissioning Authority site closure plans.

Description and Objectives.

The project is designed to support the strategic aims of the UK Nuclear Decommissioning Authority in its ongoing mission to clean-up and make safe all UK legacy nuclear sites over the next 100 years. Offsite disposal of cementitious waste is not compatible with the UK waste strategy, is very costly, and delivers little environmental benefit. It will help underpin future reuse of construction and demolition wastes in landscaping and void filling. We will explore the realisation of other associated complex value outcomes, such as management of in situ disposal facilities to capture radionuclides leached from other materials, and quantification of the rate and extent of CO2 capture occurring during carbonation reactions. It will investigate attenuation mechanisms of long-lived radionuclide (e.g. 90Sr, U) within aged and fresh crushed concrete wastes; utilising well characterised authentic materials from UK nuclear sites (e.g. Sellafield, Winfrith). It will use radionuclide contaminated sediment and crushed concrete samples from UK nuclear sites available from previous work. Further samples will also be recovered from real sites during the project. It will build on our established track-record investigating radionuclide speciation and fate, and recent projects investigating the leaching behaviour of cementitious materials.

Objective-1 will determine the mechanism of radionuclide uptake to cementitious wastes impacted by radionuclide containing leachates. Batch and flow through column experiments (with and without CO 2 ) will determine the rate and extent of radionuclide uptake from crushed concrete wastes. Radionuclide speciation and solid association will be characterised using synchrotron methods (µfocus XRF and XAS mapping,Diamond Light Source) and electron microscopy (SEM/TEM).

Objective-2 will use longer-term (12-month) experiments to investigate radionuclide retardation reactions that occur during co-disposal of cementitious wastes and already contaminated materials, (such as low-level contaminated soils) specifically exploring the role of carbonation reactions in controlling radionuclide fate and pH control.

Objective-3 will assess the carbon capture potential of cementitious wastes, both during management above ground prior to disposal and after placement in the sub-surface, using microprobe, C-isotope tracers and thermo-gravimetric analysis.

Objective-4 will use flow through column experiments to determine how the alkaline plumes produced by cementitious wastes stored at UK nuclear sites will interact with already contaminated soils and sediments, and will explore changes in radionuclide leaching rates and induced speciation changes.

Funding Information

One fully funded scholarship is available in the School of Earth and Environment in 2023/24. This 4 year scholarship is open to UK applicants and covers all student fees, a UKRI equivalent maintenance grant (this was £17,668 in 2022/23), and generous funding to support laboratory and field work (£36,000).

Eligibility Requirements

The award is open to full-time or part-time candidates (UK only). The work primarily involves laboratory experiments using waste materials collected from nuclear sites. It would suit a candidate with a background in chemistry, material science, environmental sciences, engineering or similar disciplines.

Supplementary Information

Skills Development

A series of Leeds previous Leeds PhD projects related to UK nuclear sites have produced highly qualified individuals that now work in nuclear industry related organisations (e.g. NNL, EA, Consultancy). There is an ongoing skills shortage in the nuclear sector, especially for people with experience in handling radioactive materials. The project will therefore provide training in skills spanning the boundaries of waste management, environmental geochemistry and radionuclide behaviour, which are essential for management of UK’s radioactive contaminated land legacy. The project also requires high level experimental and synthesis skills. Specifically, the project will develop understanding of contaminated ground and on-site waste management relevant to nuclear decommissioning, as well as skills in using laboratory data to underpin science-led decision making. The PhD student will develop advanced project management skills to achieve the work programme and advanced oral and written communication skills. At Leeds, generic and personal development skills programme will delivered via the Student Education Development team, augmented with internal and externally provided PhD specific training (e.g. Lab skills, PHREEQC modelling). The student will work alongside a group of 20+ researchers working on environmental geochemistry and engineering problems. The PhD student will be hosted in the Cohen Geochemistry Laboratories at the University of Leeds, but will also access high-level analytical facilities such as the LEMAS electron microscopy suite. Additional radiochemistry training and environmental analysis will be available via the NNUF RADER labs at the University of Manchester and synchrotron analysis via collaboration with Diamond Light Source. The student will be supported through weekly supervision and monthly planning meetings, and meet with external supervisors at least every 2 months. There will be placement opportunities at partner organisations and nuclear sites during the projects. We also promote a “thesis by paper” model where the thesis is organised as research paper chapters thus encouraging synthesis skills in research paper authorship, peer review, rebuttal and publication, supporting open access publication for their research findings. The researcher will also attend the annual Nuclear Decommissioning Authority Bursary Conference, and other relevant national and international conferences and workshops, again providing a professional framework for scientific exchange and network building.

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