In situ time-dependent characterisation of corrosion processes in nuclear waste storage and GDF environments

Lead Research Organisation: University of Birmingham
Department Name: Metallurgy and Materials

Abstract

The UK Government is committed to managing radioactive nuclear waste through long-term geological disposal with safe interim storage above ground. The waste will be stored in metal canisters, and corrosion is a key potential threat to their integrity throughout the process of above-ground storage, operation of the geological repository during emplacement of the canisters, and following its final closure. We plan to investigate the mechanisms and rates of a number of the likely corrosion processes, developing characterisation methods that will be generically useful for studying similar processes in the future.

Localised corrosion of metals takes place in wet environments, often in cavities under the metal surface. The commonest method for evaluating the total rate of corrosion or depth of penetration is to make a cross-section of the metal at the end of a corrosion process, so that any information on the time evolution of the shape or chemistry is lost. However, by using highly-intense X-rays from a synchrotron source, it is now possible to study these processes in situ in real time, since the X-rays can easily penetrate the water and metal surface. The 3D shape of the corrosion site can be determined with X-ray microtomography, and chemistry can be assessed with diffraction and spectroscopy. All of these techniques are available at Diamond, the UK's synchrotron facility. When these techniques are combined with advanced lab-based techniques, a full picture of the mechanisms and rates of corrosion processes will emerge, enabling the development and validation of corrosion prediction models underpinned with sound science that are necessary for underpinning policy decisions on nuclear waste storage.

Our project is a collaboration between researchers at the Universities of Birmingham, Manchester and Bristol and Diamond. A Research Fellow based at the Research Complex at Harwell (next to Diamond) will lead the research effort, co-ordinating the X-ray experiments of the PhD students based at each University, who will also use lab-based research techniques. Each will have an individual research project: these include the atmospheric corrosion and cracking behaviour of stainless steels in above-ground storage conditions, the corrosion of different stainless steels in cement containing sulfur species, and the corrosion behaviour of uranium and Magnox in cement wasteforms (all related to intermediate-level waste), and the behaviour of carbon steel in clay, which may be a candidate for storage of spent fuel. Towards the end of the programme we will explore the influence of radiation damage on some of these corrosion problems.

We will carry out the research in close collaboration with industrial and international experts in the field, who have committed to giving us informal advice in return for information on our findings at our three-monthly meetings. As our research progresses, the X-ray techniques that we are developing will become more routine, to the point where they will be taken up by industrial users who carry out contract work for both UK and international waste management programmes. The methods are also likely to be beneficial to other applications such as corrosion of reinforcing bars in concrete and corrosion of oil pipelines

We plan to hold an international workshop at Diamond on corrosion issues in nuclear waste storage to share our findings and discuss the possibility of establishing a programme of "legacy" corrosion samples that will allow monitoring of the development of corrosion in typical environments over years or even decades.

There is a continuing need for skilled researchers with knowledge in this area: we will train a research fellow and three PhD students in issues surrounding nuclear waste storage, mechanisms and modelling corrosion processes, and the use of X-ray techniques who will be able to continue this work as the country's nuclear waste strategy evolves.

Planned Impact

The UK Government's strategy for nuclear waste storage involves safe interim storage followed by eventual underground disposal. Wastes will be contained in metal canisters, and corrosion is a key threat to their integrity during above ground storage, operation of the underground storage facility, and following its closure. It is important to be able to assess the risk of corrosion at different stages. However, the timescales involved are far longer than feasible laboratory measurements, so we must develop robust, validated corrosion models based on fundamental scientific understanding in order to underpin public policy. It is important to build public confidence based on transparency and sound science since the safety of nuclear waste could impact the health and quality of life of future generations. Because this, we plan to reach out to young people through the STEM network (one investigator is trained for this), and two of us have discussed our work on BBC Breakfast and plan to continue similar communication in the media.

Understanding corrosion processes is difficult as they often take place in wet environments under the metal surface, and the main methods currently used to study them involve cutting up the metal after it has corroded. However, with highly intense synchrotron X-rays, we can probe inside the sites where corrosion is happening and monitor its evolution with time. We plan to develop these methods to understand corrosion processes that pose a risk to the integrity of nuclear waste canisters and use our data to validate corrosion models being developed by our collaborators. We will work very closely with Diamond, the UK's synchrotron: the Research Fellow leading the experimental work will be based there, working with Diamond's Physical Sciences Director, who is a co-investigator and expert in the techniques that we require.

As we develop our techniques, they will become sufficiently routine that they can be used by industrial research organisations who carry out nuclear waste-related contract research for the Nuclear Decommissioning Authority. We have a number of collaborators from such organisations who will advise us on our experimental strategy, and learn about our progress at our three-monthly meetings. They will then be able to become industrial users of Diamond, carrying out world-leading measurements, and enhancing their ability to compete for contracts from international nuclear waste management organisations, with a net benefit to the UK economy.

We have support from the Environmental Sustainability Knowledge Transfer Network to establish a web-based community group for exchanging information with the national and international research communities in this research area. This will give us a direct route for reaching out to the industrial and academic communities beyond our immediate network of collaborators. Our work will also be of value to other industries such as construction and the oil and gas sector, and to academic researchers working on modelling and experimental measurement of corrosion processes.

We plan to have an International Workshop at Diamond to inform corrosion researchers working with international waste management organisations of our new methods. As part of this workshop, we will discuss how in the future we could set up a series of "legacy" corrosion samples that could be monitored over future decades in order to validate models of some of the very slow processes involved with nuclear waste storage canisters.

It is crucial to develop skilled people to tackle these problems in future. We will train a Research Fellow and three PhD students in corrosion processes, synchrotron experiments, and underlying issues in nuclear waste storage, and the students will spend a month overseas with an international expert. Two investigators are early career academics, who will also develop skills for future success in this area.

Publications

10 25 50
 
Description We have found out how the environmental conditions in stores and microstructure of a wide range of stainless steel alloys affect the risk of corrosion of nuclear waste containers that will be stored for many decades before they are finally put underground. We have also assessed the effect of replacing the type of stainless steels used for existing container designs with duplex alloys, and have identified research strategies to inform about the impact of microstructure changes on corrosion and stress corrosion cracking. We have also determined factors that affect the long-term stability of uranium fuels under storage conditions.
Exploitation Route The work has contributed to the NDA/RWM's long-term strategy for the storage and disposal of radioactive wastes by providing technical input and scientific justification for how stores for radioactive wastes are managed (for example in terms of the influence of key environmental parameters and changing alloy microstructure on the rates of degradation) and for how wastes containing chemically reactive metals such as uranium are likely to evolve.
Sectors Energy

 
Description The work has contributed to the NDA/RWM's long-term strategy for the storage and disposal of radioactive wastes by providing technical input and scientific justification for how stores for radioactive wastes are managed (for example in terms of the influence of key environmental parameters on the rates of degradation) and for how wastes containing chemically reactive metals such as uranium are likely to evolve.
First Year Of Impact 2015
Sector Energy
Impact Types Economic,Policy & public services

 
Description Underpinning science to cause a change in the way Sellafield packages Intermediate Level Waste (ILW)
Geographic Reach Local/Municipal/Regional 
Policy Influence Type Participation in a advisory committee
Impact This will have a significant cost saving for the UK tax payer, on the order of 10's to 100's of £M.
 
Description AMEC FW Industrially funded PhD studentship (with EPSRC DTA funding) - GDF Bentonite behaviour
Amount £90,000 (GBP)
Organisation AMEC 
Sector Private
Country United Kingdom
Start 11/2015 
End 10/2019
 
Description EPSRC CDT M4DE Studentship (Supported by Sellafield Ltd.)
Amount £70,000 (GBP)
Organisation Sellafield Ltd 
Sector Private
Country United Kingdom
Start 10/2016 
End 09/2020
 
Description EPSRC CDT NGN PhD Studentship (Supported by Sellafield Ltd.)
Amount £51,000 (GBP)
Organisation Sellafield Ltd 
Sector Private
Country United Kingdom
Start 10/2015 
End 09/2019
 
Description NDA Bursary
Amount £65,000 (GBP)
Organisation Nuclear Decommissioning Authority NDA 
Sector Public
Country United Kingdom
Start 10/2014 
End 09/2017
 
Description RAEng Senior Research Fellowship/Chair
Amount £750,000 (GBP)
Organisation Royal Academy of Engineering 
Sector Learned Society
Country United Kingdom
Start 02/2016 
End 01/2022
 
Description Central Laser Facility (CLF) 
Organisation Rutherford Appleton Laboratory
Department Central Laser Facility
Country United Kingdom 
Sector Public 
PI Contribution The project involves working closely with the CLF using the Vulcan petawatt laser system to perform experiments to prove the feasibility of using a petawatt dipole pumped laser to inspect nuclear waste packages.
Collaborator Contribution The have provided access to the Vulcan laser system, assistance with co-writing and filing a patent and in developing the business case for future commercialisation of the gamma and neutron flash technology.
Impact This research collaboration has resulted in 1 paper in an international journal, 2 conference journal articles, 2 conference presentations and a patent. The collaboration has been inherently cross disciplinary due to the need for nuclear scientists, materials scientists and laser physicists.
Start Year 2016
 
Description Collaboration with CLF, Harwell 
Organisation Rutherford Appleton Laboratory
Department Central Laser Facility
Country United Kingdom 
Sector Public 
PI Contribution We worked with the CLF to conduct some 'proof of principle' experiments (May 2015) using the Vulcan Laser to demonstrate the possibility of using laser driven gamma-ray projection radiography and neutron flash measurements to examine nuclear waste packages.
Collaborator Contribution The CLF team provided access to Vulcan and led in conducting the experiments with us. They also assisted with data processing and their contracts team drew up and filed a joint patent.
Impact We have a research paper (not yet published), a patent (filed November 2015: P143188GB00) and are awaiting the outcome of an STFC IPS grant proposal for furthering the gamma scanning technology.
Start Year 2014