Biogeochemistry in Low Level Radioactive Waste Disposal

**This project is funded between NERC and LLWR Ltd. a private sector partner**

The UK has a substantial legacy of radioactive wastes as a result of its nuclear weapons and nuclear power programmes and this PhD project focusses on management of these wastes. The types of radioactive wastes are classified according to their radiological properties, and “low-level” radioactive waste forms the largest volume of waste materials destined for disposal. For low level wastes, disposal occurs at the national facility, the Low Level Waste Repository (LLWR) in west Cumbria. Safe operation and management of LLWR will be crucial to the ongoing management and decommissioning of the defunct facilities at our nuclear sites – a multi-billion programme of high national priority over the next several decades. As part of the operational licensing of LLWR, the operator has identified the need to understand the fundamental biogeochemical processes occurring within the waste and their potential impacts on contaminant behaviour. This PhD project forms part of LLWR’s forward programme to address the biogeochemical evolution of the engineered “near field” of the site and therefore to underpin the safety case for the facility over the next crucial decades.

The LLWR facility is an engineered, shallow subsurface radioactive waste disposal site which has had differing historical disposal practices over the 60+ year site lifetime. The low level radioactive wastes are mixed in character but typically contain rubble, organics and radionuclides and are packed into iron drums. Historically, the wastes have been disposed into trenches which are at neutral pH conditions and more recently disposals have been grouted and emplaced in engineered vaults at alkaline pH. The biogeochemistry of the system is complex, with reports of both Fe(III)-reduction and methanogenesis relevant to the trenches on site and with our work highlighting that radionuclide solubility under site conditions in the trenches is clearly influenced by biogeochemical processes. Our recent studies on the “extreme” high pH geomicrobiology of radioactive wastes have identified extensive microbial activity in environmental systems at pH 10 – 11 which influences stable element, organic and radionuclide/contaminant behaviour. This environmental sciences PhD will develop essential knowledge of the “extreme” biogeochemistry of the LLWR system under closure relevant conditions and where elevated pH is expected. Initially work will focus on the biodegradation of key electron donors in the wastes, and their coupling to a range of anaerobic processes in the repository environment. Latterly, the impact of these biogeochemical processes on contaminants will be explored, encompassing the identification of biodegradation pathways of key organics and the impact on the solubility of key radionuclides. Throughout, the research will couple experimental approaches with information and potentially materials from long term field scale experiments on vaults and trenches at LLWR to underpin the safety case modelling approach used for the LLWR site.

The successful researcher for this project will have a high quality first degree and / or masters degree in a relevant discipline (e.g. Chemistry, Microbiology, Environmental Chemistry, Environmental Sciences, Geochemistry or related disciplines) and join a vibrant research group in the Research Centre for Radwaste Disposal and the Williamson Research Centre at The University of Manchester. They will work with a leading team of academic and industry researchers on biogeochemistry research to solve real world issues. The successful applicant will receive a broad training including experience in biogeochemistry, microbiology, genomics, radiochemistry and mineralogy, and use national and international synchrotron facilities such as Diamond Light Source to identify the biogeochemical behaviour of the system. Upon completion, they will be well equipped for a future career in either academia or industry.