B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Thomas S.
Neill
,
Katherine
Morris
,
Scott
Harrison
,
Pete
Apps
,
Nick
Bryan
,
Stephen
Parry
,
J. Frederick W.
Mosselmans
,
Giannantonio
Cibin
,
Bruce
Rigby
,
Francis R.
Livens
,
Samuel
Shaw
Diamond Proposal Number(s):
[17243, 21441]
Open Access
Abstract: Colloids present a challenge for nuclear decommissioning and disposal due to their potential to mobilise radionuclides. Waste retrieval and decommissioning of storage ponds for spent nuclear fuel and silos for radioactive waste at the Sellafield nuclear facility, UK, are high priorities. The particulates characterised here originate from facilities >60 years old and provide a unique opportunity to investigate the long-term fate of radionuclides in an aquatic, engineered storage environment. Radioactive effluents were obtained from a legacy pond and characterised using ultrafiltration, transmission electron microscopy (TEM) and actinide L3 edge X-ray absorption spectroscopy (XAS). TEM analysis showed discrete UO2-like nanoparticles, 5-10 nm in size, often co-associated with Mg-Al- and Fe-(oxyhydr)oxide colloidal phases. Uranium XAS indicated a mix of uranium oxidation states with EXAFS suggesting U(IV)-oxide nanoparticles and sorbed U(VI). Pu XANES identified Pu(IV) as the dominant oxidation state. Both U and Pu associates with large, Mg/Al- and Fe-(oxyhydr)oxide agglomerates highlights the potential for pseudo-colloid formation, explaining the basis of current particle filtration / abatement of technology. This study, which examines novel samples from a complex, highly radioactive facility using advanced techniques, provides a new understanding of radionuclide speciation and mobility in these environments and informs radioactive effluent treatment and disposal.
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Feb 2025
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[24074, 21441]
Open Access
Abstract: Operations at uranium (U)-mining and nuclear facilities have left a global legacy of significant radionuclide contamination in groundwaters which must be managed to minimize environmental harm. Uranium groundwater contamination is present at several sites globally, including Oak Ridge National Laboratory and Hanford, USA and Sellafield nuclear site, UK. In situ phosphate biomineralisation offers a promising method for radionuclide (including 90Sr and U) remediation at these sites. Typically, phosphate-generating amendments are injected into the subsurface to sequester select radionuclides in groundwaters by precipitation of poorly soluble Ca-phosphate phases and subsequent adsorption and/or incorporation of radionuclides to these poorly soluble phases, a remediation route being explored for both U and 90Sr. In this study, we investigate the mechanisms of U-phosphate precipitation in two phosphate-generating amendments (Ca-citrate/Na-phosphate and glycerol phosphate) under conditions relevant to Sellafield, UK. Using aerobic batch sediment experiments, we show both Ca-citrate/Na-phosphate and glycerol phosphate amendments are effective at enhancing removal of U(VI) from representative groundwaters (from 94% to >97%). Aqueous geochemical data coupled to speciation modelling highlighted that precipitation of U(VI) phosphate phases was the likely mechanism of U(VI) removal from groundwaters. Further X-ray absorption spectroscopy (XAS) analysis of solids confirmed U was present as a highly insoluble uranyl orthophosphate-like phase after treatment with both Ca-citrate/Na-phosphate and glycerol phosphate amendments. These data provide underpinning information on U-phosphate remediation in Sellafield relevant conditions thus expanding the range of treatment options for radionuclide contaminated groundwaters and defining the transport and fate of U during phosphate biomineralisation.
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Feb 2025
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Rhys
Tuck
,
Younes
Chahid
,
Greg
Lister
,
Katherine
Morris
,
James
Carruthers
,
Mat
Beardsley
,
Michael
Harris
,
Michal
Matukiewicz
,
Simon G.
Alcock
,
Ioana-Theodora
Nistea
,
Carolyn
Atkins
Abstract: Additive manufacture (AM) involves creating a part layer by layer and is a rapidly evolving manufacturing process. It has multiple strengths that apply to space-based optics, such as the ability to consolidate multiple parts into one, reducing the number of interfaces. The process also allows for greater mass reduction, making parts more cost-effective to launch, achieved by optimising the shape for intended use or creating intricate geometries like lattices. However, previous studies have highlighted issues associated with the AM process. For example, when trying to achieve high-precision optical surfaces on AM parts, the latticing on the underside of mirrors can provide insufficient support during machining, resulting in the quilting effect. This paper builds on previous work and explores such challenges further. This will be implemented by investigating ways to apply AM to a deployable mirror from a CubeSat project called A-DOT. The reflective surface has a spherical radius of curvature of 682 mm and approximate external dimensions of 106 x 83 mm. The aim is to produce two mirrors that will take full advantage of AM design benefits and account for the challenges in printing and machining a near-net shape. The designs will have reduced mass by using selected internal lattice designs and topologyoptimised connection points, resulting in two mirrors with mass reduction targets of 50% and 70%. Once printed in aluminium using laser powder bed fusion, the reflective surface will be created using single point diamond turning. Finally, an evaluation of the dimensional accuracy will be conducted, using interferometry, to quantify the performance of the reflective surface.
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Aug 2024
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B18-Core EXAFS
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Diamond Proposal Number(s):
[24074]
Open Access
Abstract: Microbial ureolysis offers the potential to remove metals including Sr2+ as carbonate minerals via the generation of alkalinity coupled to NH4+ and HCO3– production. Here, we investigated the potential for bacteria, indigenous to sediments representative of the U.K. Sellafield nuclear site where 90Sr is present as a groundwater contaminant, to utilize urea in order to target Sr2+-associated (Ca)CO3 formation in sediment microcosm studies. Strontium removal was enhanced in most sediments in the presence of urea only, coinciding with a significant pH increase. Adding the biostimulation agents acetate/lactate, Fe(III), and yeast extract to further enhance microbial metabolism, including ureolysis, enhanced ureolysis and increased Sr and Ca removal. Environmental scanning electron microscopy analyses suggested that coprecipitation of Ca and Sr occurred, with evidence of Sr associated with calcium carbonate polymorphs. Sr K-edge X-ray absorption spectroscopy analysis was conducted on authentic Sellafield sediments stimulated with Fe(III) and quarry outcrop sediments amended with yeast extract. Spectra from the treated Sellafield and quarry sediments showed Sr2+ local coordination environments indicative of incorporation into calcite and vaterite crystal structures, respectively. 16S rRNA gene analysis identified ureolytic bacteria of the genus Sporosarcina in these incubations, suggesting they have a key role in enhancing strontium removal. The onset of ureolysis also appeared to enhance the microbial reduction of Fe(III), potentially via a tight coupling between Fe(III) and NH4+ as an electron donor for metal reduction. This suggests ureolysis may support the immobilization of 90Sr via coprecipitation with insoluble calcium carbonate and cofacilitate reductive precipitation of certain redox active radionuclides, e.g., uranium.
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Feb 2024
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B18-Core EXAFS
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Diamond Proposal Number(s):
[13559]
Open Access
Abstract: The past 60+ years of global nuclear activity has resulted a signifcant legacy of radioactive contaminated lands which have high economic costs associated with their remediation. Developing clean-up technologies that are environmentally friendly, economically viable and effective in the long-term is key, with in-situ remediation techniques as an important option. However, questions remain regarding the most favorable methods of remediation, and the long-term stability of any immobilised radionuclide(s). Here, we used sediment microcosms to assess the long-term (300 day) stability of immobilised U and Sr formed during anoxic microbial and chemical treatments, and assessed their stability during re-oxidation scenarios (with oxygen or nitrate additions, 100 days). We used six contrasting treatment approaches which resulted in 89 - >99%, and 65 – 95% removal efficiencies for U and Sr, respectively. These included two Zero Valent Iron (ZVI) based products (NANOFER 25S and Carbo-Iron); a slow-release electron donor (Metals Remediation Compound, MRC) to stimulate U(VI) bioreduction alongside a readily bioavailable electron donor control (lactate/acetate mix); electron donor (lactate/acetate) with elevated sulfate to stimulate metal and sulfate reduction; glycerol phosphate to promote both bioreduction of U(VI) and biomineralization of inorganic U/Sr phopshates; and finally a natural attenuation (no remediation agent added) control. X-ray Absorption Spectroscopy (XAS) revealed that whilst aqueous U was removed from solution via multiple mechanisms including sorption, reduction and incorporation, aqueous Sr was mostly removed via outer sphere complexation mechanisms. Re-oxidation with air led to increased U remobilisation (≤89%) compared to nitrate oxidation (≤73%), but neither oxygen or nitrate re-oxidation led to significant Sr remobilisation (≤38%), suggesting Sr speciation may be stable over extended timescales post remediation. Treatments amended with ZVI or glycerol phosphate not only removed the most U and Sr from solution (>99%) but they also retained the most U and Sr following re-oxidation (retaining ≥75% of the originally added U and Sr). XAS analyses suggests that enhanced immbilisation, as seen in the treatments amended with ZVI or glycerol phosphate, may be due to the U/Sr incorporation into mineral phases (i.e., iron oxyhydorxide and phospate pahses) This suggests that optimal (bio)remediation strategies should target both reduction and biomineralisation mechanisms to facilitate radionuclide-mineral incorporation, promoting longer-term stability.
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Aug 2023
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B18-Core EXAFS
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Diamond Proposal Number(s):
[24074]
Open Access
Abstract: Historical operations at nuclear mega-facilities such as Hanford, USA, and Sellafield, UK have led to a legacy of radioactivity-contaminated land. Calcium phosphate phases (e.g., hydroxyapatite) can adsorb and/or incorporate radionuclides, including 90Sr. Past work has shown that aqueous injection of Ca-phosphate-generating solutions into the contaminated ground on both laboratory and field scales can reduce the amount of aqueous 90Sr in the systems. Here, two microbially mediated phosphate amendment techniques which precipitated Ca-phosphate, (i) Ca-citrate/Na-phosphate and (ii) glycerol phosphate, were tested in batch experiments alongside an abiotic treatment ((iii) polyphosphate), using stable Sr and site relevant groundwaters and sediments. All three amendments led to enhanced Sr removal from the solution compared to the sediment-only control. The Ca-citrate/Na-phosphate treatment removed 97%, glycerol phosphate 60%, and polyphosphate 55% of the initial Sr. At experimental end points, scanning electron microscopy showed that Sr-containing, Ca-phosphate phases were deposited on sediment grains, and XAS analyses of the sediments amended with Ca-citrate/Na-phosphate and glycerol phosphate confirmed Sr incorporation into Ca-phosphates occurred. Overall, Ca-phosphate-generating treatments have the potential to be applied in a range of nuclear sites and are a key option within the toolkit for 90Sr groundwater remediation.
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Aug 2023
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B18-Core EXAFS
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Open Access
Abstract: Citrate is a key decontaminant used in the nuclear industry and here we explore its biogeochemical fate in the presence of Ni2+ and U(VI)O22+ under conditions relevant to low level radioactive waste (LLW) disposal. Anaerobic microcosm experiments were performed under nitrate- and sulfate-reducing conditions at between pH 9 and 10. Citrate (1 mM) was supplied as both an electron donor and a potential metal ion complexant. Incubation experiments with citrate, inoculated with nitrate- or sulfate-reducing microbial consortia, were challenged with three different concentrations of Ni: 0.01, 0.1 or 1 mM, or U: 0.005, 0.05, or 0.5 mM. The nitrate- and sulfate-reducing inocula were enriched from well characterised alkaline sediments obtained from high pH lime-workings. A multi-technique approach was adopted to characterise the aqueous geochemistry, solid phase mineralogy, and bacterial communities in each incubation system. In the 0.01 mM Ni systems citrate underwent full biodegradation under both nitrate and sulfate-reducing conditions in less than 15 days. In the sulfate-reducing experiments, 50% of the added 0.01 mM Ni(aq) was removed from solution and black solids formed; SEM and TEM analysis suggested that these were Ni-sulfides. For the higher Ni concentration incubations, no changes were observed in the nitrate-amended experiments. In the sulfate-amended experiments only citrate fermentation was observed, likely because elevated levels of Ni were toxic to nitrate- and sulfate-reducing bacteria in the inocula. Interestingly, although fermentative bacteria were key citrate degraders in the sulfate-amended experiments they did not dominate in the nitrate-amended experiments presumably due to competition from other microbes. In the U experiments, citrate degradation took place over 55 days in all systems except the 0.5 mM U/nitrate-amended incubations. In all U/sulfate-amended experiments, a dark-coloured precipitate formed and XAS analysis indicated that these solids contained reduced U(IV) with EXAFS suggesting that non-crystalline U(IV)–phosphate phases dominated. Microbial community analysis by 16S rRNA gene sequencing of endpoint samples identified fermenters and nitrate- and sulfate-reducing bacteria in the relevant incubations. Overall, findings suggest microbial degradation of citrate occurs under repository relevant conditions with Ni (at 0.01–0.1 mM) and U (at 0.005–0.5 mM) but with an inhibitory effect particularly at elevated Ni concentrations. Significantly, the work suggests that under anaerobic conditions relevant to LLW disposal, citrate undergoes biodegradation leading to the development of poorly soluble Ni sulfides and/or bioreduction of U(VI) to poorly soluble U(IV) phases. This suggests that both removal of citrate, and retention of Ni and U can occur in these environments and this information can be used to further inform development of safety cases for radioactive waste disposal.
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Jul 2023
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[21441]
Open Access
Abstract: In the UK, the decommissioning of legacy spent fuel storage facilities at the Sellafield nuclear facility requires the retrieval of radioactive sludge resulting from Magnox fuel corrosion. However, sludge retrievals may enhance uranium mobility including via sorption of radionuclide nanoparticles onto colloidal phases such as hydrotalcite (Mg4Al2(OH)16(CO3).4H2O). Hydrotalcite is a Mg-Al layered double hydroxide (LDH) which is a corrosion product of Magnox fuel cladding. Currently, there are a paucity of studies examining interactions between actinide nanoparticles and LDH phases such as hydrotalcite. Here, a multi-technique approach was used to investigate the interactions between colloidal hydrotalcite and three different forms of nanoparticulate U(IV): nanoparticulate uraninite (UO2); nanoparticulate UO2 reacted with silica (UO2-Si); and U(IV)-Si-coprecipitate under anoxic, neutral-to-alkaline conditions. Ultrafiltration and zeta potential analyses indicated that for UO2 and UO2-Si nanoparticulate phases, sorption to colloidal hydrotalcite was limited due to rapidly settling UO2 and UO2-Si aggregates (>450 nm). By contrast, ultrafiltration and zeta potential analyses confirmed the U(IV)-Si-coprecipitate nanoparticle phase showed significantly higher sorption to colloidal hydrotalcite. This was due to the increased colloidal stability of intrinsic U(IV)-silicate nanoparticles which in turn promoted increased sorption to hydrotalcite. TEM imaging showed some evidence for smaller UO2 and UO2-Si aggregates (<20 nm) sorbed to colloidal hydrotalcite. Similar behaviour was observed in TEM images of authentic pond effluent samples from Sellafield, providing confidence that the model laboratory experiments provided a bridge to the highly radioactive spent nuclear fuel pond interactions. This study highlights the potential for U(IV) nanoparticles to form a new type of colloid-colloid interaction with hydrotalcite, especially when silica is present. This further informs predictions of U(IV) (and An(IV)) behaviour in the legacy pond and silo environments, as well as in environmental scenarios where LDH mineral phases and silica are present (e.g. in geological disposal of radioactive waste).
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Apr 2023
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B18-Core EXAFS
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Connaugh M.
Fallon
,
William R.
Bower
,
Brian A.
Powell
,
Francis R.
Livens
,
Ian C.
Lyon
,
Alana E.
Mcnulty
,
Kathryn
Peruski
,
J. Frederick W.
Mosselmans
,
Daniel I.
Kaplan
,
Daniel
Grolimund
,
Peter
Warnicke
,
Dario
Ferreira-Sanchez
,
Marja Siitari
Kauppi
,
Gianni F.
Vettese
,
Samuel
Shaw
,
Katherine
Morris
,
Gareth T. W.
Law
Diamond Proposal Number(s):
[16611, 16939, 17243]
Open Access
Abstract: Uranium dioxide (UO2) and metaschoepite (UO3•nH2O) particles have been identified as contaminants at nuclear sites. Understanding their behavior and impact is crucial for safe management of radioactively contaminated land and to fully understand U biogeochemistry. The Savannah River Site (SRS) (South Carolina, USA), is one such contaminated site, following historical releases of U-containing wastes to the vadose zone. Here, we present an insight into the behavior of these two particle types under dynamic conditions representative of the SRS, using field lysimeters (15 cm D x 72 cm L). Discrete horizons containing the different particle types were placed at two depths in each lysimeter (25 cm and 50 cm) and exposed to ambient rainfall for 1 year, with an aim of understanding the impact of dynamic, shallow subsurface conditions on U particle behavior and U migration. The dissolution and migration of U from the particle sources and the speciation of U throughout the lysimeters was assessed after 1 year using a combination of sediment digests, sequential extractions, and bulk and μ-focus X-ray spectroscopy. In the UO2 lysimeter, oxidative dissolution of UO2 and subsequent migration of U was observed over 1–2 cm in the direction of waterflow and against it. Sequential extractions of the UO2 sources suggest they were significantly altered over 1 year. The metaschoepite particles also showed significant dissolution with marginally enhanced U migration (several cm) from the sources. However, in both particle systems the released U was quantitively retained in sediment as a range of different U(IV) and U(VI) phases, and no detectable U was measured in the lysimeter effluent. The study provides a useful insight into U particle behavior in representative, real-world conditions relevant to the SRS, and highlights limited U migration from particle sources due to secondary reactions with vadose zone sediments over 1 year.
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Dec 2022
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[21441, 24074]
Open Access
Abstract: Over 60 years of nuclear activity have resulted in a global legacy of contaminated land and radioactive waste. Uranium (U) is a significant component of this legacy and is present in radioactive wastes and at many contaminated sites. U-incorporated iron (oxyhydr)oxides may provide a long-term barrier to U migration in the environment. However, reductive dissolution of iron (oxyhydr)oxides can occur on reaction with aqueous sulfide (sulfidation), a common environmental species, due to the microbial reduction of sulfate. In this work, U(VI)–goethite was initially reacted with aqueous sulfide, followed by a reoxidation reaction, to further understand the long-term fate of U species under fluctuating environmental conditions. Over the first day of sulfidation, a transient release of aqueous U was observed, likely due to intermediate uranyl(VI)–persulfide species. Despite this, overall U was retained in the solid phase, with the formation of nanocrystalline U(IV)O2 in the sulfidized system along with a persistent U(V) component. On reoxidation, U was associated with an iron (oxyhydr)oxide phase either as an adsorbed uranyl (approximately 65%) or an incorporated U (35%) species. These findings support the overarching concept of iron (oxyhydr)oxides acting as a barrier to U migration in the environment, even under fluctuating redox conditions.
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Nov 2022
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