What is your PhD project about?

Plutonium, a radioactive element, is produced in nuclear reactors as one of the by-products of nuclear energy. The UK now has a 120 tonne stockpile of plutonium. The current plan for this stockpile is to reuse the majority as a special type of nuclear fuel called “mixed oxide” or “MOX” fuel, while the remainder will be disposed of underground in a geological disposal facility.

Before radioactive plutonium can be disposed of, it must first be conditioned into a safe and stable form, called a wasteform, which is then placed inside several outer packages before being disposed deep underground and backfilled. The wasteform can be made by incorporating the plutonium into another material, with ceramics being the best option at present. Because plutonium will be radioactive for over 100,000 years the material we choose must be stable for very long periods of time, especially in terms of how it interacts with groundwater which it may eventually come into contact with if the outer barriers are penetrated.

The purpose of my PhD project is to understand how these materials change over time once they come into contact with groundwater and how well they can keep hold of the radioactive plutonium.

Why did you choose your PhD discipline?

Since halfway through my chemistry undergrad, I’ve been fascinated by nuclear science. Very strange things happen on atomic scales! I wanted to use this interest in a way that could help advance science and society, so nuclear energy was the obvious option.

Why did you choose your institution?

The Immobilisation Science Laboratory at Sheffield is a known hub for nuclear science in the UK and is very well-equipped for nuclear research. It has strong connections in the nuclear community and opens doors for plenty of interesting collaborative research.

How will your PhD contribute to the safety case for a UK GDF?

One of the main concerns people have with building a GDF and disposing of plutonium underground is whether it is safe. Demonstrating that the wasteforms proposed for plutonium disposal can remain stable and retain plutonium for geological timescales is an important part in both building a safety case and reassuring the public that the strategy is safe.

What has been the best thing about the project so far?

As a CDT student, I’ve had a chance to learn about all aspects of nuclear energy, even beyond the scope of waste disposal. Having this multidisciplinary learning has been very interesting and useful!

What has been the most challenging thing about the project so far?

Condensing information into concise reports/reviews. It can be difficult to convey a message in the shortest way possible.

What do you wish you’d known before starting this project?

The major importance of reading in a PhD! I feel I am a slow reader when it comes to scientific papers, a skill which I am now developing but would have been useful to build up before starting.

What are your plans after your PhD?

At this stage it’s too early to tell but there are a few good options. Continuing research in academia, moving to industry or working in government on nuclear policy.

What have been the benefits of NWS sponsorship for the project?

I am very grateful to NWS for funding my PhD which is part of a larger NWS project investigating plutonium evolution to help build a safety case for its disposal. This is very interesting because it means having the freedom of an ordinary PhD in terms of the depth and level of detail we can explore, but still being industrially relevant and knowing the outcomes will be useful in contributing to the development of the GDF.

What advice can you offer to future NWS PhD students?

Don’t be afraid to take some good time at the start of your PhD to read very deeply into the literature. Being familiar with the key research before you start will help you understand where the knowledge gaps are and how your research can contribute.

We look forward to sharing more about Ismail’s research progress in the future.

What is your PhD project about?

Despite the very first generation of commercial nuclear power reactors now being retired, we still need to dispose of the inventory of the spent nuclear fuel. For decades spent fuel has been held in interim storage facilities, requiring frequent maintenance and monitoring. Much of this nuclear waste will remain radioactive for thousands of years. It is therefore naive and arguably unethical to rely on future generations to carry the burden of continuing to store this waste safety and effectively.

In England and Wales the accepted solution is to construct a geological disposal facility deep underground. Such a facility will aim to isolate nuclear waste for hundreds of thousands of years, by which time the radioactive waste will have decayed to safe background levels of radioactivity.

My PhD aims to investigate how uranium, used in nuclear fuel, would corrode and behave over thousands of years and under the evolving conditions of a geological disposal facility, for example in different types of groundwater and oxygen concentration. Uranium corrosion is important to investigate to ensure the safety of a disposal facility, both in the short- and long-term. We need to be confident that radioactive uranium corrosion products do not seep into the groundwater and escape the facility, and that toxic corrosion products do not form in a way in which endangers the safety of the facility.

Why did you choose your PhD discipline?

I am a firm believer that nuclear power is vital for achieving net zero in the UK by 2050. However, I also believe that the nuclear waste problem is one of the biggest hurdles to overcome and this tarnishes the reputation of the nuclear industry.

Why did you choose your institution?

I recently completed a MSc at Bristol where I was introduced to academics in the nuclear field and the great scene of community. Bristol has a lot of active research in my field and there are countless nuclear sector industries on their doorstep.

How will your PhD contribute to the safety case for a UK GDF?

Metallic uranium readily reacts with many species. There has been extensive research into how uranium reacts with oxygen and water, and the formation of uranium hydride, but there is limited research on specifically how uranium is likely to corrode in evolving GDF conditions. For example, we need to predict the rate of uranium hydride formation because it is highly toxic and pyrophoric, meaning it can spontaneously catch fire in the presence of oxygen. This could pose a significant hazard, especially in the pre-closure phase where staff could be in relatively close proximity to the waste; particularly important for the short-term safety of the GDF.

We also need to understand how pond water evolves into GDF groundwater as it interacts with the waste and waste containment. We must then investigate how the pH and chemical constituents of this groundwater could interact with the uranium, for example in leaching studies. Groundwater is one of the main mechanisms by which radioactive isotopes could escape a GDF, and so it is important for the long-term safety of a GDF that leaching of uranium into the groundwater is limited.   

What is the most interesting finding from your project?

I am only at the start of my PhD and because of COVID I haven’t yet been able to conduct any research in the labs. However, I have been doing a lot of reading and learning about how a GDF is likely to evolve over time and uranium corrosion in water and uranium hydride formation. I am now writing a literature review to encapsulate all previous research in GDF conditions and relevant uranium science. 

What has been the best thing about the project so far?

The best thing about my research is how important it is and therefore how motivated I feel. This research is a crucial part to the ultimate disposal of nuclear waste.

What has been the most challenging thing about the project so far?

The most challenging part so far has been learning how to use a computer modelling program called GEANT4. This has been a very steep learning curve and I still have a long way to go. However, the lack of resources online means that it is even more satisfying when it works!

What do you wish you’d known before starting this project?

I wish I had known that progress can often feel slow because each task is often a lot of work! I wish I had been more realistic when setting personal goals and deadlines.

What are your plans after your PhD?

I currently plan to leave academia and work as a waste behaviour expert either as part of a consultancy or somewhere, like Radioactive Waste Management, which is heavily involved in the management/disposal of nuclear waste.    

What have been the benefits of NWS sponsorship for the project?

NWS are at the front-line of making a GDF a reality in the UK. They have already published many reports on topics such as the evolution of spent nuclear fuel, particularly for oxide fuels, and waste packages, which have proved invaluable to my reading of literature so far. They have also been a very useful, relevant and easily understandable reference for everything you could want to know about hosting a GDF in the UK.

What has been the most surprising thing to come out of your PhD?

I am always surprised by what I didn’t know there was to know. Over this year I have become more familiar with the Dunning–Kruger effect, especially when it comes to uranium science. Basically, there is so much more to know than I ever thought possible, and the way to manage this is to identify what you need to know and what exactly is relevant to your research.

What advice can you offer to future NWS PhD students?

Make sure you can convince yourself why your research project is important to society. By understanding how your research will contribute to a better world, this will keep you more motivated and give your life enhanced meaning.

You can find out more about Rosie’s research on her university page. We look forward to sharing the outcomes of Rosie’s research in the future. 

What is your PhD project about?

In the UK, we are going to bury our nuclear reactor waste deep underground in order to protect ourselves and future generations from its radiation. It will remain underground and in a secure Geological Disposal Facility (GDF) for thousands of years. We already understand a lot about the waste going into the GDF and can predict how it will interact with its environment for many years to come. Most of it will remain locked away even after the man-made barrier breaks down after hundreds of thousands of years, due to the reactions with the waste that will happen underground.

Iodine, however, is a particularly mobile part of nuclear waste, and at the moment we are unsure if it could move through the environment, and eventually travel up to the plants we eat and the air we breathe. This would be harmful to life on Earth due to waste iodine’s radioactivity. I am using our current knowledge of the reactions iodine takes part in deep underground with soil, minerals and microorganisms to determine whether iodine will move to the surface and be harmful, or whether its interactions will actually prevent its movement and limit the harm it could cause.

Why did you choose your PhD discipline?

I enjoy the multidisciplinary aspect of my PhD, my background is in chemistry but I have had the chance to research a variety of new topics, from nuclear reactor cores to soil water migration.

Why did you choose your institution?

I did my undergraduate studies at the University of Manchester and really enjoyed my time here. UoM has an excellent nuclear research faculty, and I also love the city

How will your PhD contribute to the safety case for a UK GDF?

The results of my PhD will give further insight into the movement of iodine in the environment. This will give a more accurate prediction of iodine movement in years to come, and so can be considered in the safety case. It should highlight any conditions making iodine more susceptible to transport in the deep sub surface, and if there is a need for mitigating action. 

What do you wish you’d known before starting this project?

That everything in the environment is a lot more complex than the chemistry experiments you do in the lab! Who knew that soil was such a complex matrix of interacting matter and organisms, the U.S Soil Taxonomy has a series of over 19,000 soil systems!

What are your plans after your PhD?

Luckily, I think it’s a little early for me to be thinking about that! I can see myself in the nuclear industry, but I think my project will give me a lot of transferable skills so hopefully the world will be my oyster.

We look forward to sharing more about Meg’s research progress in the future.

What is your PhD project about?

I basically study how nuclear waste glass dissolves. In the UK we carefully turn our used nuclear fuel into oil-drum sized blocks of dark radioactive waste glass, a process called vitrification. Glass is a great material as it immobilises the radioactive particles in a safe and stable form.  This glass is currently securely stored in protective steel canisters in controlled facilities before it will be disposed of for all eternity in a specialised UK site up to 1 km underground. There will be around 8,000 canisters to be disposed of; sealed in thick metal containers. Over hundreds of thousands of years, the metal containers may eventually corrode, allowing deep groundwater to contact the glass and the possibility that it will slowly dissolve the glass. Disposing of nuclear waste glass deep underground is by far the safest and the most environmentally friendly solution, however we need to know how this glass could dissolve and to predict the radioactive particle release rate to responsibly inform future generations of the state of the local environment.

The dissolution of nuclear waste glass depends on its constituent elements (containing up to 2/3 of the periodic table!) and elements in the groundwater. I particularly focus on the roles of zinc and calcium as these elements have an important role on the dissolution process – over time zinc can cause the glass to turn into clay and calcium can help form a protective glassy-gel layer that can prevent further dissolution. The interplay of zinc and calcium isn’t well understood, yet.

Why did you choose your PhD discipline?

As a physics undergraduate student I developed a fascination of the civil nuclear industry. I wanted to understand the fundamental science a lot more, particularly aspects of nuclear waste, especially those generated from the Chernobyl disaster and how we can dispose of this waste safely.

Why did you choose your institution?

The University of Sheffield is one of the world’s leaders in the development and testing of nuclear waste forms.

How will your PhD contribute to the safety case for a UK GDF?

My PhD will provide dissolution data from the inactive high-level-waste glass (CaZn MW), which is currently being produced in the UK. This glass has been dissolved in pure water to underpin the fundamental mechanisms of corrosion, which can be used as input for future predictive computer modelling of the dissolution behaviour.

We have also generated dissolution data in environments similar to a GDF, in potential groundwaters/near field materials and have considered different corrosion scenarios, such as dissolution in vapour directly followed by liquid contact. Preliminary results positively suggest that despite differing corrosion scenarios and environments, the glasses dissolve at a low rate in the short to medium term (0-3 years), but results indicate that the combined effects of zinc, magnesium and iron need to be further studied, particularly over longer term dissolution (3-100,000 years of disposal – captured from longer dissolution tests and computer modelling) to generate a robust safety case.

Have you had any significant outcomes from the project?

Winning the Roy G. Post Foundation Scholarship in 2019 for my work and contributions to waste management.

What has been the best thing about the project so far?

Working within a helpful community whose knowledge base and contacts were endless. Also the opportunity to travel to conferences was invaluable – putting your work into practical perspective and inspiring you to do greater things.

What has been the most challenging thing about the project so far?

There is never enough time to fully explore all your ideas.

What do you wish you’d known before starting this project?

World leading academics and industry personnel are so approachable. I wish I’d contacted people sooner for advice, tips and guidance, or even emailing authors of academic publications for clarification. Everyone I contacted took the time to respond with great information. The PhD extends far beyond your institution and country.

What are your plans after your PhD?

In the short term I’d like to transfer some of my ideas into conducting and developing research, be that in academia or industry. In the long-term I’d definitely like to be involved in the GDF project.

What have been the benefits of NWS sponsorship for the project?

Guidance from NWS was great, narrowing down subject areas that need investigating for the safety case. I liked the idea of performing applicable, yet fundamental science, which NWS directed, but given artistic licence for the means of data generation.

It was great to work for a government institution on a major infrastructure project. I learnt a lot about how such a large organisation functions as well as learning so much more outside of my specific subject area, not just in science, but in policy.

What has been the most surprising thing to come out of your PhD?

Taking a placement at IAEA HQ in Vienna as part of the Pre-Disposal Team in the Waste Technology Section. Invaluable experience was gained working in an international team on Chernobyl, Fukushima and disused radioactive sealed sources projects. I forever will be appreciative of having had this opportunity.

What advice can you offer to future NWS PhD students?

Really seek and understand the literature – use all this wealth of knowledge to guide your work to strengthen areas of the disposal safety case that need addressing.

Make sure some of your work can be directly added to the existing data set for effective comparisons. But also try something new, think outside the box.

You can read more about Adam’s work in his publications on ResearchGate.

What is your PhD project about?

My PhD work aimed to understand how sulfide affects the mobility of uranium in the subsurface around a geological disposal facility. In the deep subsurface, where radioactive waste is planned to be disposed of, microorganisms are naturally present and some of these (known as sulfate-reducing bacteria) can produce sulfide. Sulfide can react with contaminants, like uranium, as well as the naturally occurring minerals, such as iron oxyhydroxides, and cause significant changes to the system. If we want to implement geological disposal of radioactive waste safely, it’s important to understand how this process, known as sulfidation, impacts the environmental mobility of contaminants including uranium.

Luke Townsend working in the laboratory

Why did you choose your PhD discipline?

I wanted to undertake a PhD that had a specific, ‘real world’ problem that needed addressing (rather than a fundamental study as some PhDs are). I also was attracted to the multidisciplinary aspect of the work (including, chemistry, physics, mineralogy, microbiology, etc.)

Why did you choose your institution?

I chose Manchester as the supervision for the project provided by Kath Morris, Sam Shaw, and Jon Lloyd, was some of the best in the world. The group produces some of the highest quality and highest impact science in this area of environmental science so the opportunity was too good to pass on.

How will your PhD contribute to the safety case for a UK GDF?

My PhD work aided in building the safety case for GDF implementation by providing fundamental, relevant research into how uranium will behave in a sulfidation environment, post-closure of the GDF. My studies focussed on producing high quality, highly controlled experiments that investigated how the chemistry of uranium was affected in these environmental scenarios by mimicking these processes in the laboratory. This included performing highly controlled chemistry-based experiments using state of the art equipment (known as a chemostat), as well as performing microbiological investigations.

The results of these studies will aid in informing NWS’s models for how a GDF may evolve over 10s to 100s of 1000s of years in the future and will enable a greater understanding of uranium will potentially move within the subsurface.

Tell us about a key finding of your research?

Here, we investigated some curious uranium chemistry involved in the sulfidation process and through extensive investigations we actually believe that it’s caused by a new form of uranium that we termed a U(VI)-persulfide. This was a really exciting finding as something like this hasn’t been discovered before in an environmental scenario.

What has been the best thing about the project so far?

The interesting work has pushed me to develop both my academic and personal skills, providing me with the opportunity to expand my area of expertise (from just chemistry) and present my work to academic and industrial colleagues around the world.

What has been the most challenging thing about the project so far?

Learning to balance to needs of academia with the requirements of industry (NWS) can be challenging but is also probably one of the most useful skills that I obtained during my PhD. You can design the perfect experiment in the lab but if it’s not relevant to the problem you’re trying to solve/the needs of NWS then it’s not much use. It’s difficult to strike the balance between these things, particularly when designing experiments early on in the PhD, but it’s immensely useful to be able to do so (a valuable transferable skill) and is really satisfactory when it all comes off in the end.

What do you wish you’d known before starting this project?

That things will go wrong when you’re doing research but that’s okay! Experiments will fail, results won’t look right, and things will seem nonsensical at times, but this is all part of the process when you’re pushing the boundaries of science and exploring uncharted territory. I struggled with the idea of being comfortable with failure initials but it’s learning from these experiences that is the most invaluable lesson during your PhD.

What are your plans after your PhD?

Currently undertaking an EPSRC Doctoral Prize Fellowship extending this line of work, with NWS providing a letter of support for the project.

What have been the benefits of NWS sponsorship for the project?

Having NWS as a sponsor has given me the opportunity to tailor my work towards ‘real world’ problems (which I believe is very important in both science and the nuclear industry) whilst also being able to explore interesting areas of research. Learning this balance between academia and industry focusses was a very useful skill to acquire. Additionally, I’ve been fortunate enough to meet interesting and important colleagues through NWS (eg. Cherry Tweed), with the further benefit of the financial support taking me around the world to gain invaluable life and professional experiences.

What has been the most surprising thing to come out of your PhD?

My work getting covered in the media. Highly unexpected, but seeing your work printed in the newspaper is pretty exciting!

What advice can you offer to future NWS PhD students?

Probably the same advice as I quoted above about becoming okay with the difficulties and the failures you’ll endure throughout your PhD.

You can read more about Luke’s work in his publications on ResearchGate.

What is your PhD project about? Geological disposal is the preferred option for the long-term management of radioactive waste by many countries, including the United Kingdom (UK). A Geological Disposal Facility (GDF) is based on a multi-barrier concept, which uses a series of engineered barriers that provide physical and chemical containment for radioactive waste, mitigating the potential for radionuclide release to the geo- and bio-spheres. Cementitious materials are used for many different parts of the multi-barrier GDF, having a wide range of purposes, for example as waste encapsulate, as backfill or as a sealant. In my project, we tried to understand how two different cementitious materials, a high-pH cement considered to be used as a backfill material in one of the UK GDF conceptual scenarios for the disposal of intermediate level waste (Nirex Reference Vault Backfill, NRVB), and a low-pH cement considered for use by many European countries (called Cebama reference cement), performed when in contact with three different groundwater compositions (granitic, saline and clay). Understanding the mineralogical evolutions of these cementitious materials, especially when in contact with groundwater, is key for the development of a robust safety case.

BSE images of ettringite needles (a) in NRVB sample that was in contact with clay groundwater for 6 months (high magnification); (b) in NRVB sample that was in contact with saline groundwater 6 months.

Why did you choose your PhD discipline? I had just finished my master’s degree in environmental sciences, when I came across this PhD position. I thought it was an interesting area where I could use the background knowledge that I had on waste disposal. I also thought that it was a practical area, where the discoveries that we make could be directly applied to real world problems. Why did you choose your institution? The University of Sheffield is well known for their world leading research in the area of radioactive waste management/disposal. How will your PhD contribute to the safety case for a UK GDF? With the work performed during my PhD, it was possible to demonstrate the feasibility of using the different cementitious materials in the GDF context when in contact with groundwater. In the case of NRVB, the main purpose of this cementitious material is to provide a high-pH environment when in contact with groundwater. Independently of the groundwater composition, this was observed. These results are of significance to the UK GDF concept where this backfill material is considered to be used, in a crystalline rock. In the case of Cebama reference cement paste, this cementitious material was designed to provide a lower pH environment when interactions with the geological environment/engineered barriers occur, especially in a clay context. The buffering of the solutions to a low-pH was obtained in the current work. Additionally, when carbonates were present, the formation of a protective layer was observed and resulted in a reduction of the interaction with the groundwaters. These results are of great importance for many European safety cases, where clay/bentonite barriers are considered for use, as this protective layer will reduce possible interactions of the cementitious material with the groundwater. And therefore, this will reduce the probability of changes in the structure of the cement occurring that might affect the cement’s overall performance. What has been the best thing about the project so far? Being able to work in a diverse and friendly group, where I was able to learn a lot from the large range of research on radioactive waste disposal. Having supervisors that supported me every step of the way. The possibility to travel to different countries to present my work. Also, during my PhD I was able to collaborate with different institutions, not only from the UK but also from Europe. What has been the most challenging thing about the project so far? My PhD project was based on long-term experiments (3 years), i.e. these experiments ran from the start until almost the end of my PhD. As such, in the beginning of my PhD I had to come up with an innovative experimental set-up to get good results for my project. This ended up being quite stressful. What do you wish you’d known before starting this project? I wish I would have more pre-knowledge on cement, as my PhD was heavily focussed on cement chemistry and it might had made my life easier in the beginning of my PhD. Nevertheless, it was a very interesting area to focus my studies. What are your plans after your PhD? After finishing my PhD, I got a position as a consultant at NSG Environmental, a company that delivers decommissioning and waste management solutions to many nuclear licensed sites. What have been the benefits of NWS sponsorship for the project? Being sponsored by NWS meant that my PhD project was kept industrially relevant, by providing guidance and insight on the current needs of the nuclear industry. Also, the project would not have happened without NWS’s funding. What has been the most surprising thing to come out of your PhD? Meeting different people from different countries and backgrounds, and learning from / alongside them. Also, being considered an expert in cement leaching. What advice can you offer to future NWS PhD students? Don’t be scared of getting into a project in an area where you don’t have much experience. If you have a good supervisor (like I had), this will easily be overcome. You can read more about Rita’s work in her publications on ResearchGate.