Characterisation and Decontamination of Radioactive Stainless Steel Waste

Nuclear decommissioning programmes across the world have highlighted the requirement for a greater understanding of how radionuclides interact and become bound to the surface of materials. The volume of waste arising from decommissioning activities is predicted to be substantial; therefore cost, safety and environmental drivers all exist to reduce the volume of all types of radioactive waste requiring disposal. Contaminated metals make up a significant proportion of the waste inventory as components (such as pipework, vessels and structural beams) become contaminated during nuclear operations. In 2016, the Nuclear Decommissioning Authority (NDA) reported that there is approximately 32,000 tonnes of contaminated intermediate level waste (ILW) stainless steel that exists in the UK alone. At a current predicted rate of ~£70,000/m3 to dispose of ILW, this volume of waste adds up to a considerable cost liability (~£300m) that will need to be funded by the UK taxpayer. When other forms of metallic waste are taken into account, as well as waste arising from outside the UK, this value becomes significantly larger and the size of the challenge apparent.
A thorough understanding of the nature of waste materials is of vital importance for the nuclear sector in order to reduce the cost of decommissioning. Through helping stakeholders to understand their challenges, more informed decisions can be made when planning decommissioning operations and selecting decontamination procedures. The work proposed in this project supports the selection of the most appropriate decommissioning strategies and also feeds into the selection of materials in future nuclear facilities. Therefore, this project initially aims to extensively characterise a number of real active plant samples utilizing state-of-the-art facilities with supporting work to establish mechanistic understanding of contamination processes. This will inform decontamination strategies which will be tested in this work.

Project Outline
The project will involve two key stages:
Stage 1 - The focus of this stage will be to fully characterize a small number of contaminated stainless steel specimens obtained from real plants. Supporting work exploring the nature of the contamination of these plant samples will be performed under lab scale controlled conditions using simulant contaminating solutions. Initiatives such as Sellafield's active demonstrator programme would be an ideal opportunity for the student to study 'real-life' active material and generate a new stock of knowledge for a key nuclear stakeholder. Opportunities for this collaboration will be arranged through Sellafield's Integrated Project Teams. High resolution analytical techniques will be required for this work due to the very low concentration of radioisotopes that are expected on these materials. This in turn means access to specialised equipment at facilities such as NNL, Diamond Light Source and Manchester's radiochemistry laboratories will be required.

Stage 2 - Following the characterisation of the targeted specimens, the focus of this project will switch to the decontamination. It is well recognised in the nuclear sector that a 'toolbox' of decontamination technologies will be required to fully decommission the entire NDA estate. However, studies often only focus on one technology and it is often difficult to select the most appropriate technique without direct comparison. Through applying several appropriately selected decontamination processes to the same contaminated specimen the pros and cons of each techniques can be determined and recommendations made to the industry. This work will also enable the decontamination technologies studies to progress to industrial deployment.

EPSRC Research Area: Nuclear Fission (under the Energy theme)