Vitrified nuclear waste durability in complex natural environments

Lead Research Organisation: University of Sheffield
Department Name: Materials Science and Engineering

Abstract

Understanding the long-term durability of nuclear waste glass in the subsurface is important in the UK and internationally as many countries intend to dispose of vitrified radioactive waste in underground geological disposal facilities. In order to ensure safe disposal, we need to be confident that radioactive elements will remain isolated and immobilised for sufficient time to allow radioactivity to decay to safe levels. There will be multiple barriers in place (e.g. a metal container and engineered backfill) to delay groundwater from reaching the nuclear waste glass but eventually contact with water is expected. Although there are a number of laboratory tests currently used to determine the rate of glass dissolution in water all accelerate corrosion by increasing the temperature, surface area, or both and give very different predictions depending on the test conditions. Laboratory tests are also performed under simplified, stable, sterile conditions and using deionised water taking no account of how changing geochemical conditions will affect glass corrosion rates. This fellowship will combine materials science, geochemistry and geomicrobiology to study how glass corrodes in real-time in dynamic complex natural environments. I will improve understanding of key factors affecting corrosion (temperature, groundwater geochemistry, saturation, and microbiology) using the Ballidon long duration experiment, where glass samples have been buried for nearly 50 years. To predict the durability of nuclear waste glass thousands of years into the future I will study simulant nuclear waste glass's in conditions relevant to UK and US disposal concepts. The result of this novel investigation will be to critically evaluate, and improve, upon durability tests for glass, to build an improved model of glass corrosion and to establish further long duration experiments to inform the safety case for geological disposal in the UK and abroad.

Planned Impact

My research into glass durability in complex natural environments will directly impact upon beneficiaries in the UK nuclear industry including governmental policy makers 'Radioactive Waste Management' (RWM) responsible for carrying out the government's policy to dispose of high level vitrified waste in a Geological Disposal Facility (GDF). The fellowship directly addresses three key areas within RWM's "Geodisposal Science and Technology Plan 2016" and advances understanding of vitrified waste dissolution under UK relevant burial conditions. Furthermore, through improvements to current dissolution tests, this research will benefit companies developing glass compositions under consideration for the immobilisation of UK legacy intermediate level waste streams (e.g. Geomelt Ltd, National Nuclear Laboratories and the University of Sheffield). Improved low temperature dissolution tests will be investigated as part of this fellowship and could be applied to non-heat generating vitrified intermediate level wastes.
This science is also of interest to policy makers abroad particularly the US Department of Energy, responsible for disposal of US vitrified radioactive wastes. The study of glass dissolution under variable saturation, low temperatures, and changing groundwater composition (work packages 2-5) is pertinent to the safety case for a newly constructed Integrated Disposal Facility for low activity waste at the Hanford Site, Washington State, US. In addition, a number of US simulant glasses have been buried at the Ballidon site (the main natural analogue site studied) and the advanced site characterisation proposed during this fellowship will assist in interpretation of corrosion on those samples. Beneficiaries include Pacific North-West National Laboratories and Savannah River Laboratories who are both involved in ongoing research into US glass durability and collaborative work with the UK. In Europe, my findings and method development will be of interest to other countries working towards geological disposal of vitrified radioactive wastes and at a similar or more advanced stage of GDF implementation including France, Belgium, Sweden and Finland.

This research advances the underpinning science for the proposed UK GDF and, therefore, may help to answer questions posed by environmental groups and members of the public concerned with the safe disposal of vitrified radioactive waste. This research is timely as the RWM will begin another round of consultations in 2018 to allow potential volunteer communities to come forward to discuss hosting the UK GDF. This body of research will contribute to the underpinning science available for members of the public to access during this consultation phase.

Despite the applied nature of this fellowship experiments will advance the fundamental understanding of glass corrosion that may also interest other communities concerned with glass durability. For example work package 3, investigating the role of microorganisms in glass corrosion, may be of interest to archaeologists interesting in ancient glass sample preservation. Furthermore, improved prediction of glass durability under a range of geochemical conditions may interest commercial glass manufacturers (e.g. for the construction industry, semiconductors, scientific instruments).

Publications

10 25 50
 
Title Vitrified Nuclear Waste Sculpture 
Description Designed in collaboration with blacksmith artist John Mallett, this sculpture represents the structure of the glass network within a steel nuclear waste canister. The work is comprised of glass and steel and intended to be transported to outreach events and, in the meantime, displayed in the Turner museum of glass, University of Sheffield. 
Type Of Art Artwork 
Year Produced 2021 
Impact None yet, it has just been completed 
 
Description A number of natural analogue glasses have been studied including glasses from the shipwreck of the Albion, the Ballidon glass burial experiment and Peak Dale Cave. Differences have been observed between glass samples altered in a complex natural environment and those altered using simplified laboratory test methods. In particular the roll of elements coming from the groundwater and adjacent minerals are found to be important as elements like Fe, P and Mg are sequestered even if not present in the glass. These elements have the potential to affect the dissolution rate of glass through controlling the mineralogy of the alteration layer. Alteration textures appear different between simple and complex environments with biology implicated in preferential corrosion of glass.

In preliminary experiments where glass was exposed to microbial metabolism, enhanced dissolution was observed and work is ongoing to unpick the mechanisms for this.
Exploitation Route Work is in early stages. I will write more on this next year.
Sectors Energy,Environment

URL https://www.envchemgroup.com/natural-analogues-nuclear-waste.html
 
Description HADES: A User Facility for High Activity Decommissioning Engineering Science
Amount £658,445 (GBP)
Funding ID EP/T011424/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2020 
End 05/2023
 
Description Platform for Long-term Experimental Investigation of Alteration in Disposal Environments and Storage - PLEIADES
Amount £597,980 (GBP)
Funding ID EP/V035215/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 08/2021 
End 09/2023
 
Description Royal Society of Chemistry Grants for Carers
Amount £610 (GBP)
Organisation Royal Society of Chemistry 
Sector Charity/Non Profit
Country United Kingdom
Start 09/2019 
End 11/2019
 
Description Royal Society of Chemistry Research Fund
Amount £2,973 (GBP)
Funding ID R20-4913 
Organisation Royal Society of Chemistry 
Sector Charity/Non Profit
Country United Kingdom
Start 02/2021 
End 02/2022
 
Description Project GLAD: Glass leaching Assessment for Disposability 
Organisation U.S. Department of Energy
Department Pacific Northwest National Laboratory
Country United States 
Sector Public 
PI Contribution Monthly meeting to discuss aspects of the GLAD project, review manuscripts, co-author manuscripts and co-supervise a PDRA from October 2020.
Collaborator Contribution Co-authoring manuscripts, sharing and discussing new data, contributing to a review of glass alteration testing. Sharing of samples LAW A44, ISG, and a high phosphate sample. Co-authoring of a Smithsonian Volume on the Hill Fort project.
Impact Publication: Smithsonian Volume (multi-disciplinary) Glass science, archaeology, environmental science. Publication: VALIDATION AND USE OF A pH-DEPENDENCE LEACHING TEST FOR EVALUATION OF LOW ACTIVITY NUCLEAR WASTE GLASSES
Start Year 2019
 
Description Project GLAD: Glass leaching Assessment for Disposability 
Organisation Vanderbilt University
Country United States 
Sector Academic/University 
PI Contribution Monthly meeting to discuss aspects of the GLAD project, review manuscripts, co-author manuscripts and co-supervise a PDRA from October 2020.
Collaborator Contribution Co-authoring manuscripts, sharing and discussing new data, contributing to a review of glass alteration testing. Sharing of samples LAW A44, ISG, and a high phosphate sample. Co-authoring of a Smithsonian Volume on the Hill Fort project.
Impact Publication: Smithsonian Volume (multi-disciplinary) Glass science, archaeology, environmental science. Publication: VALIDATION AND USE OF A pH-DEPENDENCE LEACHING TEST FOR EVALUATION OF LOW ACTIVITY NUCLEAR WASTE GLASSES
Start Year 2019
 
Description The Hillfort Project 
Organisation U.S. Department of Energy
Department Pacific Northwest National Laboratory
Country United States 
Sector Public 
PI Contribution Monthly meeting are held virtually to discuss the progress of the Hillfort Project and to showcase results from the project. Future directions are discussed and possible additional natural analogues that could be used. Representatives from the University of Sheffield are present at all of these meetings and contribute frequently including to reviewing publication outputs from this project. We have also shared best practice on sample preparation and new experimental techniques.
Collaborator Contribution The Hillfort project is run and funded by PNNL and researchers from the University of Sheffield (myself and Russell Hand) take the part of advisers and reviewers of the data. The team at PNNL are investigating both vitrified hillfort material and iron age slag alongside collaborators from Sweden, Israel, US and UK.
Impact The collaboration is multi-disciplinary encompassing glass/materials science, geochemistry, microbiology and archaeology. There have been a number of academic publications from this work one of which was published this year and included in the publication section and two that are in the submission process. The collaboration is also writing a publication for the Smithsonian museum that is due out next year. The Hillfort Project is tied into the GLAD project which aims to change the test used to accept vitrified radioactive waste into the Integrated Disposal Facility at the Hanford site USA. This will have an impact on policy at the site.
Start Year 2019
 
Description Natural analogues for nuclear waste: a window into the future? 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact I was invited to write an article for the Environmental Chemistry Interest Group. ECG Bulletin July 2021. This article is available to the public online but also circulated to members of the special interest group. This article has lead to a science journalist requesting an interview about a longer article for a special issue of physics world.
Year(s) Of Engagement Activity 2021
URL https://www.envchemgroup.com/natural-analogues-nuclear-waste.html