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One of the most significant challenges facing modern society is to balance the growing demand for power with the dwindling supply of fossil fuels, our primary energy supply. Meeting this challenge will require a combined approach ranging from making better and more efficient use of existing resources and exploring alternative sources of energy, a key component of which is nuclear power. Approximately 11% of the world’s electricity is produced through nuclear fission power, and it is an increasingly important factor in helping to reduce CO2 emissions in line with international targets.
In recent decades, the use of nuclear energy has prevented gigatonnes of carbon dioxide being released when compared with non-renewable energy. With proven capability as an alternative to fossil fuels, nuclear fission is likely to remain a central component of efforts to prevent future climate change. The use of nuclear power presents numerous challenges with safety and radioactive waste management key considerations.
An area of nuclear research of particular importance in the UK is the field of nuclear decommissioning and radioactive waste management. As a nation, we have accumulated radioactive waste from a variety of sources including nuclear power stations, the use of radioactive materials in medicine, industry, and research, and also from defence-related military programmes which need to be disposed of in a safe and secure manner.
The majority of waste products are considered to have low-level toxicity (94%), which we can already dispose of safely with 6% classed as intermediate-level waste. Less than 1% of radioactive waste is classed as high-level waste. However, although the total volume is relatively small it contains around 95% of the total activity1 which can take hundreds of thousands of years to decay to safe levels. How best to manage this waste is a topic of much debate and significant nuclear research is currently focused on developing safe and effective solutions.
Key to the UK’s strategy for disposal is the plan for a Geological Disposal Facility (GDF). Under this plan, highly radioactive waste, immobilised in cement would be interred deep underground. The nuclear waste will be radioactive for 100,000s of years so understanding the processes in order to optimise its containment is paramount.
In order for this approach to be successful, it is important to anticipate the impact of the high-level waste on the surrounding environment. Research into the behaviour of nuclear materials at all stages of the fuel cycle is critical in order to develop effective predictive models.
The UK’s synchrotron science facility, Diamond Light Source, is a hub for renewable energy and energy recycling research, but less well known are its applications as a centre of excellence for nuclear research. Work in this area is transforming our energy future by making the nuclear fuel cycle safer, more efficient and more straightforward to use.
Professor Fred Mosselmans, Principal Beamline Scientist at beamline I20, has been involved in much of the nuclear research at Diamond. He has worked in X-ray absorption spectroscopy for over 30 years and he is applying his knowledge to assist numerous projects at Diamond that will find out how best to store radioactive waste.
Prof Mosselmans explains: “Finding volunteers for a site for the GDF is likely to take several more years and in the next year or two host communities could be identified. We have to make sure that the facility will last and by using the synchrotron we can predict at a molecular scale what will happen to the radionuclides as the GDF inevitably degrades over thousands of years.”
1 World Nuclear Association http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-wastes/radioactive-waste-management.aspx
The safe treatment and disposal of hazardous materials relies on an improved understanding resulting from a combination of experiments, theory, and predictive modeling, the key foundations of nuclear research.
Techniques available at Diamond can prove useful in various aspects of nuclear research including structural and electronic characterisation of radioactive materials, investigations of ion-exchange materials for nuclear waste remediation, examination of features within bulk samples, such as cracks, pores, precipitates, and phases of different compositions. It is also possible to perform element-specific detection of contaminants even at very low concentrations (down to ppm under certain conditions).
Broadly grouped into diffraction (for structural information), spectroscopy (for chemical information), and imaging (to monitor vulnerabilities in nuclear waste storage materials such as crack formation in corrosive environments), the nuclear research techniques available at Diamond can provide information about a large number of different sample types including metallic solids, ceramics and glasses, hydrocarbons, heterogeneous systems, humid and damp systems, and chlorinated materials.
A key advantage of the facilities at Diamond is the ability to perform in situ experiments that probe a material during a chemical reaction or physical process. Examples relevant to nuclear research include the effects of radiation on interfacial processes and real-time investigation of corrosion processes.
Details of some of these research projects conducted at Diamond are detailed below.
Diamond has launched an active materials laboratory alongside the synchrotron.
This new facility significantly improves the capabilities for researchers, and provides users with the flexibility to safely prepare and manipulate samples on-site. Not only will this save time, money, and reduce the potential for contamination, it will also enable users to perform experiments that were previously impossible in the UK.
This new facility will transform what our user community can do as they will not need to go back and forth between their home laboratories to reload their sample cells or reprocess their samples. The impact of prolonged radiation on the mechanical performance of a range of materials such as graphite and Zircaloy used in fission and fusion facilities will be of great interest to our user community. Similarly, understanding the corrosion impact of radionuclide behaviour in encapsulated nuclear waste is essential to model and understand the future performance of the UK's proposed geological disposal facility; to do so requires intimate knowledge of the interaction of radionuclides with the materials used in the construction of the facility.
Dr Fred Mosselmans, Principal Investigator
A team from the National Nuclear Laboratory, led by Dr Helen Swan, used Diamond to understand the long-term effectiveness of nuclear fuel cladding materials. They applied a combination of XRF and XANES on I18 beamline to identify the chemical distribution and speciation in zirconium alloys. The insight gained from this study will have a fundamental impact on the development of fuel cladding in the future, increasing fuel efficiency while retaining or improving reactor safety.
“In order to investigate the oxidation states of Fe – an alloying element important for Zircaloy nuclear fuel cladding in terms of corrosion resistance – we were recommended to use the XANES technique combined with the specialised micro-sized beam available on I18. The success of this initial experiment and the brilliant support of Diamond staff was key to NNL performing further experiments at Diamond on other beamlines, in the knowledge that we would be exceptionally supported throughout.” Dr Helen Swan, Senior Research Technologist (Materials Science), Materials and Reactor Chemistry, National Nuclear Laboratory
The University of Bristol has been using Diamond for some time now to investigate the fall-out from the Fukushima nuclear power plant disaster.
Most recently a team led by Prof. Tom Scott, in partnership with the Japan Atomic Energy Agency (JAEA) examined samples collected close to the site, within the restricted zone. The team was keen to understand the physical and chemical nature of the radioactive particles and determine their long-term environmental fate and the risks they posed.
Using a combination of tomography and micro-fluorescence measurements from I13-1 and I18 beamlines at Diamond, they were able to analyse the internal structure and 3D elemental distribution of the radioactive particle, all in parallel. The results will be used to influence the decommissioning strategies on the accident site to mitigate any adverse effects to both humans and the environment.
Prof. Tom Scott, and a group of scientists from the University of Bristol, have been investigating the behaviour of intermediate-level radioactive waste (ILW) storage drums at Sellafield.
"A small proportion of the waste drums have begun to exhibit external distortions after 30 years in storage, so we worked with Diamond to simulate on a small scale what was happening inside the containers," he said.
“We made thin matchsticks of uranium and corroded them inside grout to analyse the corrosion products at the Joint Engineering, Environmental, and Processing (JEEP) beamline, I12. No one had done these experiments before; this was cutting-edge science where we observed the build-up of corrosion products in situ, on the beamline.”
The corrosion products of uranium take up considerably more space than the precursor metal and their expansive development inside the grout-filled waste drums is likely to explain why distortions were being observed on their outsides. Now armed with the findings of Prof. Scott’s ground-breaking study, Sellafield has undertaken to reconsider the design of how some of the historical legacy waste is packaged in the future. Prof. Scott comments: “Our research indicated that internal expansion inside the drums caused by corrosion of waste metals will induce cracking of the contained grout at a relatively early stage in life. Hence a simpler packaging strategy which doesn’t use grouting may provide a more cost-effective option.”
Supported by this and other complementary nuclear research carried out by the National Nuclear Laboratory (NNL) and Sellafield Ltd. within an existing long-term programme, it was recently announced that Sellafield will cut down a 22-step packaging process for some legacy ILW to just 3 or 4 steps. This is a more cost-effective way of interim waste storage, offering taxpayer savings in the order of several £100M.
As well as monitoring how radioactive waste interacts with storage containers, it is important to predict how it might interact with the environment when a storage facility eventually degrades after thousands of years. Professor Katherine Morris has dedicated her research to understanding how radionuclides behave in complex systems.
One project, funded by the Natural Environment Research Council, focused on biogeochemical processes in the alkaline environments relevant to nuclear waste disposal. Prof. Morris explains: “We reacted alkaline soil samples with uranium and found that bacteria could operate in these conditions. As we hypothesised, they had a positive effect and reduced the uranium down to a less-soluble form so that it was retained and prevented from being transported.” In collaboration with Professor Jon Lloyd, Head of the University of Manchester’s Geomicrobiology Group, Prof Morris is now isolating the bacteria that possess these amazing properties and they hope to study them further at Diamond.
Prof. Morris’ group used one of Diamond’s spectroscopy beamlines, B18, to study how radionuclides, including transuranic materials, which arise from nuclear processes, combine and interact at the atomic level with natural minerals and microbes in the earth. In order to protect the surrounding environment, it is vital to understand the impact that radioactivity in the waste could have as the disposal facility gradually evolves over millennia. The group’s results indicate that both minerals and microbial activity can actually act to provide a barrier to radionuclide migration in many systems.
In another aspect of nuclear research at Diamond, Prof. Morris and her team have used a combination of small-angle X-ray scattering (SAXS) and X-ray absorption spectroscopy (XAS) to probe the interactions of radionuclides with cement over long time periods. Their work focused on the formation of uranium colloids in synthetic cement leachate systems. The information they have gained from these experiments can be applied directly to the management and decommissioning of radwastes and ensuring safe and effective disposal of radioactive materials over the long term.
If you have a particular project in mind or are interested in hearing more about how Diamond may be able to help with your work, please complete an enquiry form or phone us on 01235 778797 - we'd love to hear from you.
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