Special Issue "The Development and Use of Synchrotron Radiation Techniques for the Geological Disposal of Radioactive Wastes"

A special issue of Geosciences (ISSN 2076-3263).

Deadline for manuscript submissions: closed (30 November 2018)

Special Issue Editors

Guest Editor
Dr. Pieter Bots

Civil and Environmental Engineering, University of Strathclyde, UK
Website | E-Mail
Interests: environmental engineering; geochemistry; colloidal nanoparticles; actinides; fission products; environmental mineralogy; geological disposal; legacy nuclear wastes
Guest Editor
Dr. Andrea Hamilton

Civil and Environmental Engineering, University of Strathclyde, UK
Website | E-Mail
Interests: cement chemistry; materials science; materials degradation; mineralogy; porous materials; nuclear waste disposal; synchrotron XRD

Special Issue Information

Dear Colleagues,

In many countries such as the UK and France, the nuclear energy sector plays a vital role in achieving energy security and reducing the emission of greenhouse gasses as outlined in the Paris agreement. For viable and safe operation of the nuclear energy sector, however, long-term management strategies with a safety case based on scientific evidence need to be in place for the radioactive wastes produced (and legacy wastes from six decades of nuclear power generation). The preferred route for the long-term management of radioactive wastes is through the disposal within geological disposal facilities in deep geological formations. Such facilities will need to be designed to minimize the likelihood of radioactive substances contaminating the environment. This will be achieved using a multi-barrier concept. Within such a concept, several barriers will be in place to inhibit groundwater from reaching the wastes and to retain radioactive substances within a geological disposal facility. Such barriers include the waste forms, backfill materials after the wastes have been safely stored within the facility, the structural engineering materials of the facility itself, and the host rock in the vicinity of the geological disposal facility.

The design of such a geological disposal facility will need to be supported by a safety case based on the most up-to-date scientific understanding of the behaviour of such a facility within deep geological formations. Synchrotron radiation techniques (e.g., X-ray spectroscopy, diffraction, scattering, tomography, and fluorescence spectroscopy) play an increasingly important role in research on the geological disposal of radioactive wastes. In this Special Issue of Geosciences, we aim to showcase the use and development of state-of-the-art synchrotron radiation techniques in order to enhance our understanding of the behaviour of potential geological disposal facilities for nuclear wastes and how wastes, actinides and fission products behave within such a facility and the surrounding environment.

The use and development of synchrotron radiation techniques in this Special Issue can be applied to the example topics listed below:

  • Interaction of actinides and fission products with engineered materials and host rock mineralogy
  • Stability of nuclear waste forms and novel encapsulation materials during the lifetime of a geological disposal facility
  • Potential radionuclide transport mechanism in a geological disposal facility
  • Mineralogical stability of engineering materials in geological disposal settings
  • The geochemistry and microbiology of natural analogues

Dr. Pieter Bots
Dr. Andrea Hamilton
Guest Editors

Manuscript Submission Information

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Keywords

  • Synchrotron radiation
  • Actinides
  • Fission products
  • Geological disposal
  • Nuclear waste
  • Structural materials
  • Host rock
  • Natural analogues
  • Energy

Published Papers (5 papers)

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Research

Open AccessArticle Fifteen Years of Radionuclide Research at the KIT Synchrotron Source in the Context of the Nuclear Waste Disposal Safety Case
Geosciences 2019, 9(2), 91; https://doi.org/10.3390/geosciences9020091
Received: 16 December 2018 / Revised: 28 January 2019 / Accepted: 29 January 2019 / Published: 15 February 2019
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Abstract
For more than 120 years, systematic studies of X-ray interaction with matter have been the basis for our understanding of materials—both of natural or man-made origin—and their structure-function relationships. Beginning with simple radiographic imaging at the end of the 19th century, X-ray based [...] Read more.
For more than 120 years, systematic studies of X-ray interaction with matter have been the basis for our understanding of materials—both of natural or man-made origin—and their structure-function relationships. Beginning with simple radiographic imaging at the end of the 19th century, X-ray based analytical tools such as X-ray diffraction, X-ray fluorescence and photoemission or X-ray absorption techniques are indispensable in almost any field of chemical and material sciences—including basic and applied actinide and radionuclide studies. The advent of dedicated synchrotron radiation (SR) sources in the second half of the last century has revolutionized the analytical power of X-ray probes, while—with increasing number of SR facilities—beamline instrumentation followed a trend towards increasing specialization and adaption to a major research topic. The INE-Beamline and ACT station at the KIT synchrotron source belong to the exclusive club of a few synchrotron beamline facilities—mostly located in Europe—dedicated to the investigation of highly radioactive materials. Since commissioning of the INE-Beamline in 2005, capabilities for synchrotron-based radionuclide and actinide sciences at KIT have been continuously expanded, driven by in-house research programs and external user needs. Full article
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Open AccessArticle Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface
Geosciences 2019, 9(2), 81; https://doi.org/10.3390/geosciences9020081
Received: 23 November 2018 / Revised: 9 January 2019 / Accepted: 1 February 2019 / Published: 8 February 2019
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Abstract
Neptunium and uranium are important radionuclides in many aspects of the nuclear fuel cycle and are often present in radioactive wastes which require long term management. Understanding the environmental behaviour and mobility of these actinides is essential in underpinning remediation strategies and safety [...] Read more.
Neptunium and uranium are important radionuclides in many aspects of the nuclear fuel cycle and are often present in radioactive wastes which require long term management. Understanding the environmental behaviour and mobility of these actinides is essential in underpinning remediation strategies and safety assessments for wastes containing these radionuclides. By combining state-of-the-art X-ray techniques (synchrotron-based Grazing Incidence XAS, and XPS) with wet chemistry techniques (ICP-MS, liquid scintillation counting and UV-Vis spectroscopy), we determined that contrary to uranium(VI), neptunium(V) interaction with magnetite is not significantly affected by the presence of bicarbonate. Uranium interactions with a magnetite surface resulted in XAS and XPS signals dominated by surface complexes of U(VI), while neptunium on the surface of magnetite was dominated by Np(IV) species. UV-Vis spectroscopy on the aqueous Np(V) species before and after interaction with magnetite showed different speciation due to the presence of carbonate. Interestingly, in the presence of bicarbonate after equilibration with magnetite, an unknown aqueous NpO2+ species was detected using UV-Vis spectroscopy, which we postulate is a ternary complex of Np(V) with carbonate and (likely) an iron species. Regardless, the Np speciation in the aqueous phase (Np(V)) and on the magnetite (111) surfaces (Np(IV)) indicate that with and without bicarbonate the interaction of Np(V) with magnetite proceeds via a surface mediated reduction mechanism. Overall, the results presented highlight the differences between uranium and neptunium interaction with magnetite, and reaffirm the potential importance of bicarbonate present in the aqueous phase. Full article
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Open AccessArticle Plutonium Migration during the Leaching of Cemented Radioactive Waste Sludges
Geosciences 2019, 9(1), 31; https://doi.org/10.3390/geosciences9010031
Received: 30 November 2018 / Revised: 21 December 2018 / Accepted: 24 December 2018 / Published: 8 January 2019
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Abstract
One of the most challenging components of the UK nuclear legacy is Magnox sludge, arising from the corrosion of Mg alloy-clad irradiated metallic U fuel that has been stored in high pH ponds. The sludges mainly comprise Mg hydroxide and carbonate phases, contaminated [...] Read more.
One of the most challenging components of the UK nuclear legacy is Magnox sludge, arising from the corrosion of Mg alloy-clad irradiated metallic U fuel that has been stored in high pH ponds. The sludges mainly comprise Mg hydroxide and carbonate phases, contaminated with fission products and actinides, including Pu. Cementation and deep geological disposal is one option for the long-term management of this material, but there is a need to understand how Pu may be leached from the waste, if it is exposed to groundwater. Here, we show that cemented Mg(OH)2 powder prepared with Pu(IV)aq is altered on contact with water to produce a visibly altered ‘leached zone’, which penetrates several hundred microns into the sample. In turn, this zone shows slow leaching of Pu, with long-term leaching rates between 1.8–4.4 × 10−5% of total Pu per day. Synchrotron micro-focus X-ray fluorescence mapping identified decreased Pu concentration within the ‘leached zone’. A comparison of micro-focus X-ray absorption spectroscopy (µ-XAS) spectra collected across both leached and unleached samples showed little variation, and indicated that Pu was present in a similar oxidation state and coordination environment. Fitting of the XANES spectra between single oxidation state standards and EXAFS modeling showed that Pu was present as a mixture of Pu(IV) and Pu(V). The change in Pu oxidation from the stock solution suggests that partial Pu oxidation occurred during sample ageing. Similarity in the XAS spectra from all samples, with different local chemistries, indicated that the Pu oxidation state was not perturbed by macro-scale variations in cement chemistry, surface oxidation, sample aging, or the leaching treatment. These experiments have demonstrated the potential for leaching of Pu from cementitious waste forms, and its underlying significance requires further investigation. Full article
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Open AccessArticle Neptunium Reactivity During Co-Precipitation and Oxidation of Fe(II)/Fe(III) (Oxyhydr)oxides
Geosciences 2019, 9(1), 27; https://doi.org/10.3390/geosciences9010027
Received: 23 November 2018 / Revised: 14 December 2018 / Accepted: 14 December 2018 / Published: 8 January 2019
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Abstract
Fe(II) bearing iron (oxyhydr)oxides were directly co-precipitated with Np(V)O2+ under anaerobic conditions to form Np doped magnetite and green rust. These environmentally relevant mineral phases were then characterised using geochemical and spectroscopic analyses. The Np doped mineral phases were then oxidised [...] Read more.
Fe(II) bearing iron (oxyhydr)oxides were directly co-precipitated with Np(V)O2+ under anaerobic conditions to form Np doped magnetite and green rust. These environmentally relevant mineral phases were then characterised using geochemical and spectroscopic analyses. The Np doped mineral phases were then oxidised in air over 224 days with solution chemistry and end-point oxidation solid samples collected for further characterisation. Analysis using chemical extractions and X-ray absorption spectroscopy (XAS) techniques confirmed that Np(V) was initially reduced to Np(IV) during co-precipitation of both magnetite and green rust. Extended X-Ray Absorption Fine Structure (EXAFS) modelling suggested the Np(IV) formed a bidentate binuclear sorption complex to both minerals. Furthermore, following oxidation in air over several months, the sorbed Np(IV) was partially oxidised to Np(V), but very little remobilisation to solution occurred during oxidation. Here, linear combination fitting of the X-Ray Absorption Near Edge Structure (XANES) for the end-point oxidation samples for both mineral phases suggested approximately 50% oxidation to Np(V) had occurred over 7 months of oxidation in air. Both the reduction of Np(V) to Np(IV) and inner sphere sorption in association with iron (oxyhydr)oxides, and the strong retention of Np(IV) and Np(V) species with these phases under robust oxidation conditions, have important implications in understanding the mobility of neptunium in a range of engineered and natural environments. Full article
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Open AccessArticle Synchrotron-Based Micro-CT Investigation of Oxic Corrosion of Copper-Coated Carbon Steel for Potential Use in a Deep Geological Repository for Used Nuclear Fuel
Geosciences 2018, 8(10), 360; https://doi.org/10.3390/geosciences8100360
Received: 14 August 2018 / Revised: 17 September 2018 / Accepted: 20 September 2018 / Published: 26 September 2018
Cited by 1 | PDF Full-text (7622 KB) | HTML Full-text | XML Full-text
Abstract
Within the multi-barrier system proposed for the permanent disposal of used nuclear fuel, the primary engineered barrier is the sealed metallic container. The present Canadian container design utilizes a carbon steel vessel coated with Cu for corrosion protection. In the event of a [...] Read more.
Within the multi-barrier system proposed for the permanent disposal of used nuclear fuel, the primary engineered barrier is the sealed metallic container. The present Canadian container design utilizes a carbon steel vessel coated with Cu for corrosion protection. In the event of a defect in the Cu coating that exposes the steel substrate, galvanically accelerated corrosion of steel is, in principle, possible. In this work, the progression of corrosion at a simulated through-coating defect in 3.0 mol/L NaCl solution containing dissolved O2 was monitored using electrochemical measurements and imaged non-destructively using synchrotron X-ray micro computed tomography (micro-CT). The damage volume at the base of the simulated defect was measured from the 3D micro-CT data and used to calculate the amount of O2 used to drive steel corrosion. The results demonstrate that the availability of O2 determines the rate and overall extent of corrosion, while the coatings produced using different deposition and treatment methods (cold spray deposition, heat-treated cold spray deposition, electrodeposition) lead to different corrosion propagation geometries, with the distribution of damage depending on the quality of the Cu/steel interface. Full article
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