Characterisation and Decontamination of Radioactive Stainless Steel Waste

Lead Research Organisation: University of Manchester
Department Name: Chem Eng and Analytical Science

Abstract

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)

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S513842/1 30/09/2018 29/09/2024
2108993 Studentship EP/S513842/1 02/09/2018 29/09/2022 Daniel Barton
 
Description Long term corrosion studies of 304 stainless steel in highly concentrated nitric acid with contaminants such as cobalt, cesium and strontium have shown that corrosion rates are not notably increased. The presence of cerium has enhanced corrosion rates slightly. Corrosion rates in all circumstances were linear for approximately 45 days and have since exhibited exponential increases due to the presence of corrosion products (Fe(III), Cr(IV)) enhancing corrosion rates.

Corrosion and contamination studies of the steel in boiling nitric acid have so far shown that cobalt concentration makes no difference to corrosion rate.
Exploitation Route Contamination mechanisms aim to be identified through work prior to completion. If contamination mechanism is identified, along with the knowledge that certain contaminants do not enhance corrosion on a long term basis, suitable chemical decontamination techniques can be presented to industry, which could dramatically enhance decontamination times, and minimise waste.
Sectors Chemicals,Energy,Environment

 
Description Collaboration with National Nuclear Laboratory 
Organisation National Nuclear Laboratory
Country United Kingdom 
Sector Public 
PI Contribution We have provided an experimental programme that attempts to emulate nuclear operations, as much as reasonably practicable, that result in radioactive contaminated steel materials. Prepared materials are thoroughly characterised to improve understanding of contamination processes and the likely nature of resultant contamination. The prepared materials will then be utilised to test likely decontamination strategies. This information will be used by NNL to help inform nuclear operators like Sellafield Ltd on decontamination and decommission strategies for nuclear plants at their end of life.
Collaborator Contribution NNL has provided supervision for the PhD student on this project, giving direction on immediate industrial (e.g. Sellafield Ltd) interests on contaminated systems and likely decontamination options being considered. Will also supply plant samples for interrogation and testing to allow comparisons to simulant conditions and systems.
Impact A previous iCASE award closely associated with this current project has delivered the following publication outputs. 1) T. Kerry, A. W. Banford, W. Bower, O. R. Thompson, T. Carey, J. F. W. Mosselmans, K. Ignatyev and C. A. Sharrad (2018) Uranium contamination of stainless steel in nuclear processing plants, Ind. Eng. Chem. Res. 57, 3957-3962. DOI: 10.1021/acs.iecr.7b05139 2) T. Kerry, A. W. Banford, O. R. Thompson, T. Carey, D. Schild, A. Geist and C. A. Sharrad (2017) Transuranic Contamination of Stainless Steel in Nitric Acid, J. Nucl. Mater., 493, 436-441. DOI: 10.1016/j.jnucmat.2017.06.033 3) R. Muniz, L. Lobo, T. Kerry, C. A. Sharrad, and R. Pereiro (2017) Depth profile analysis of rare earth elements in corroded steels by pulsed glow discharge - time of flight mass spectrometry, J. Anal. At. Spectrom. 32, 1306-1311. DOI: 10.1039/c7ja00171a The research delivered in this previous project has been utilised by Sellafield Ltd in assessing the likely nature of contamination of materials in the THORP reprocessing plant an and inform decontamination processes to support the decommissioning strategy. It is anticipated that this current project will also deliver similar impact.
Start Year 2013