B18-Core EXAFS
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Diamond Proposal Number(s):
[37736]
Open Access
Abstract: 99Tc is a long-lived radioactive fission product whose subsurface mobility is governed by redox conditions. Under oxic conditions, soluble Tc(VII)O4– is mobile, whereas under reducing conditions, poorly soluble Tc(IV) phases limit transport. Microcosm studies have frequently reported TcO2-like solids and, less consistently, Tc(IV)-sulfides. The stability of Tc(IV)-sulfides under environmentally relevant conditions remains unclear. Here, we used flowing sediment columns representative of the Sellafield subsurface to examine Tc speciation and stability over ∼1 year. Under reducing conditions, >90% of added TcO4– (400 μg) was retained under both Fe(III)- and sulfate-reducing conditions. X-ray absorption spectroscopy showed TcO2-like phases dominated in Fe(III)-reducing columns, while Tc(IV)-sulfides dominated after sustained sulfate reduction. Sequential extractions indicated that Tc in sulfidic sediments was more recalcitrant (≤23% released by weak acids) than in Fe(III)-reducing systems (∼60% released). With oxic groundwater pumping, effluent Tc sourced from the sediments rose rapidly. Over 160 days, the sulfidic columns remobilized ∼25% of their Tc inventory compared to ∼50% in Fe(III)-reducing columns. The Tc(IV)-sulfides also gradually oxidized to form TcO2 phases. While Tc(IV)-sulfides may enhance Tc retention under reducing conditions, TcO2 phases more likely govern 99Tc mobility during long-term redox cycling. Our findings provide new constraints for modeling Tc fate at contaminated sites and in radioactive waste disposal.
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Dec 2025
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I19-Small Molecule Single Crystal Diffraction
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Thien D.
Duong
,
Jiangnan
Li
,
Ruohan
Li
,
Xin
Lian
,
Yinlin
Chen
,
Jiarui
Fan
,
Joseph
Hurd
,
Lixia
Guo
,
Daniel
Lee
,
Mark
Warren
,
Sihai
Yang
Diamond Proposal Number(s):
[41123]
Abstract: The capture of xenon (Xe) and krypton (Kr) from the off-gas of used nuclear fuel is of great importance to the treatment of radioactive wastes and production of high purity Xe. Solid sorbents, in particular metal–organic frameworks (MOFs), show promise in gas capture. However, the unknown radiation resistance of MOFs has limited their development. Herein, the efficient capture and separation of Xe/Kr by MFM-520, which strikes a remarkable stability toward 1750 kilogray (kGy) γ-irradiation, is reported. Under ambient conditions, dynamic breakthrough experiments confirm the efficient separation performance, yielding a Xe capacity of 66 and 0.2 mg g−1 from a by-product of air separation (Xe/Kr: 20/80; v/v) and off-gas (Xe/Kr: 400/40 ppm balance in air), respectively. In situ synchrotron X-ray single crystal diffraction and solid-state nuclear magnetic resonance (ssNMR) studies reveal that the optimal micropore of MFM-520 underpins specific host-guest interactions to Xe, resulting in selective Xe capture.
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Oct 2025
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B18-Core EXAFS
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Diamond Proposal Number(s):
[33573]
Open Access
Abstract: Borosilicate glass is a potential candidate for high-level radioactive waste conditioning, thus understanding the effects caused by the combined presence of uranium and actinides within these matrices is of great importance. The glass matrix was simultaneously loaded with UO3 and lanthanide oxides (CeO2, Nd2O3, and Eu2O3) as chemical surrogates for actinides. Neutron diffraction in combination with Reverse Monte Carlo simulation confirmed that the basic glass structure is comprised of tetrahedral SiO4, and BO3/BO4 units. X-ray absorption spectroscopy indicated the presence of Ce mainly as CeIII and the co-existence of UV and UVI. U acts as an intermediate oxide and reduces the number of four-coordinated B, lanthanide ions serve as modifiers, with their increasing concentration shifting the B-O coordination from 3 to 4. X-ray photoelectron spectroscopy revealed a depth-dependent variation in the UIV/UVI ratio. Leaching tests showed increased dissolution of Si, B, and Na, compared to the glass matrix.
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Aug 2025
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B18-Core EXAFS
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Diamond Proposal Number(s):
[37736]
Abstract: There is a requirement to further understand the structural and thermal properties of candidate Pu wasteform materials, and moreover gain a better understanding of composition-driven variation in these properties as they can impact disposability. Zirconolite (CaZrTi2O7) phases are a candidate wasteform system to immobilise Pu at scale and therefore it is necessary to understand (as far as possible) the isolated influence of cation substitution on specific lattice sites. CaZr1-xHfxTi2O7 is a model system for understanding the microstructural effects of Hf4+ substitution and underpin its viability as a neutron absorbing additive that could feasibly be co-immobilised with Pu. Hf4+ was capable of wholly substituting for Zr4+ at low-to-moderate concentration (i.e. x ≤ 0.60) after which some minor Hf-phase segregation was observed. Powder X-ray diffraction, Rietveld analysis and Raman spectroscopy were consistent with Hf4+ substituting in the Zr4+ site and confirmed no additional zirconolite polytypes were formed in addition to 2M. Hf L3-edge EXAFS analysis was consistent with Hf4+ occupying the 7-fold Zr4+ site in the zirconolite-2M structure consistent with the targeted substitution scheme. The thermal diffusivity and thermal conductivity of the zirconolite ceramics was generally observed to increase with elevated Hf4+ content although no clear compositional trends were identified.
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Aug 2025
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B18-Core EXAFS
I14-Hard X-ray Nanoprobe
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You Cheng
Khng
,
Gianni F.
Vettese
,
Satoshi
Utsunomiya
,
Joyce W. L.
Ang
,
Jessica M.
Walker
,
Julia
Parker
,
Thomas
Neil
,
Katherine
Morris
,
Liam
Abrahamsen-Mills
,
Mirkka
Sarparanta
,
Gareth T. W.
Law
Diamond Proposal Number(s):
[31916, 31395]
Open Access
Abstract: Uranium dioxide (UO₂) particles can be released from mines, nuclear fuel manufacturing, reactor accidents, and weapons use. They pose inhalation risks, yet their behavior in the human lung remains poorly understood. This study investigates the long-term chemical alteration and dissolution of µm-sized UO₂ particles in two model lung fluids: Simulated Lung Fluid (SLF) and Artificial Lysosomal Fluid (ALF), representing extracellular and intracellular lung environments, respectively. Particles were exposed to each fluid at 37°C for up to 180 days (SLF) and 900 days (ALF). In SLF, UO₂ showed low apparent solubility (<2% U released to solution), but solid-phase analyses revealed significant oxidation of U(IV) (~50%) and formation of autunite-like sheets on the UO2 surface. Secondary phase formation may lessen overall UO2 dissolution, promoting long-term particle retention, whilst modifying particle chemical toxicity and cell uptake. In contrast, Monte Carlo simulations indicate that the SLF-induced surface alteration would reduce (>50%) external radiation dose from the particles. In contrast, UO₂ readily dissolved in ALF (~75% uranium released to solution in 60 days, ~100% by 900 days). There was no evidence of secondary phase formation in ALF, but extensive particle matrix dissolution/disaggregation was observed by 30 days. Fragmentation of the UO2 polycrystalline matrix may lead to release of smaller UO₂ crystallites, which could translocate more readily. Overall, this work provides new mechanistic insight into the fate of inhaled UO₂ under physiologically relevant conditions, highlighting a possible need to consider particle reactivity and alteration processes in health risk assessments.
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Aug 2025
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B18-Core EXAFS
I14-Hard X-ray Nanoprobe
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[25930, 24074, 21441]
Open Access
Abstract: Uranium (U) is a natural radioactive metal and a persistent environmental pollutant. Characterising the influence of arbuscular mycorrhizal fungi (AMF) on U bioaccumulation and partitioning in plants is crucial to understand U soil-to-plant transfer mechanisms. High resolution elemental mapping, spectroscopy and microscopy techniques were conducted on uranyl nitrate dosed Plantago lanceolata roots colonised with Rhizophagus irregularis. U-rich particles accumulated within the root cells, with higher abundance in epidermal and outer cortex cells of mycorrhizal root samples than in non-mycorrhizal roots. Electron microscopy determined two different crystalline U phases, an acicular crystal and a novel rounded aggregate formation, the latter of which was only found within the mycorrhizal root cells. Multiple imaging and spectroscopic techniques enabled the dominant elements with these U biominerals to be determined. Co-localisation between U, phosphorus and oxygen indicated the dominance of U-phosphate biominerals, but metals including calcium and zinc were also found to co-localise. The most dominant U compound was uranyl orthophosphate, likely accompanied by autunite. This study demonstrates alteration in U localisation and U particle morphology within Plantago roots as a direct consequence of AMF colonisation. This knowledge will allow more accurate U food-chain transfer modelling and better assessment of AMF-assisted phytoremediation feasibility.
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Jun 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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B18-Core EXAFS
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Diamond Proposal Number(s):
[23343]
Abstract: Geopolymers are promising materials for safe immobilisation and disposal of complex radioactive waste streams. This work investigates the effect of Sr incorporation and alkali-activator chemistry on 1) geopolymer chemistry, phase assemblage and nanostructure, 2) chemical binding mechanism of Sr2+ into the aluminosilicate framework of (N,K)-A-S-H gels in geopolymers, and 3) mass transport of Sr2+ during leaching, using high-field solid-state nuclear magnetic resonance spectroscopy and synchrotron-based X-ray absorption spectroscopy measurements. All geopolymers studied comprise a fully polymerised, X-ray amorphous Al-rich (N,K)-A-S-H type gel. Si exists predominantly in tetrahedral Q4(4Al) and Q4(3Al) sites and Al exists in tetrahedral sites, resulting in a net negative charge that is balanced by Na+ and/or K+ in extra-framework sites. Sr2+ was incorporated into extra-framework sites within (N,K)-A-S-H gels, without altering the local structure of the aluminosilicate framework by directly substituting for both Na+ and K+ in charge-balancing sites to form a (N,K,Sr)-A-S-H gel, at loadings equal to or below Sr/Na = 0.005. Above this limit, SrCO3 is formed, and the geopolymers simultaneously chemically bind Sr within a (N,Sr,K)-A-S-H gel, and physically encapsulate excess Sr as SrCO3. These findings have significant implications for use of geopolymers as materials for encapsulation and/or immobilisation of radioactive waste containing 90Sr.
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Feb 2025
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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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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[19223]
Abstract: High-charge micas exhibit improved adsorption properties and are a promising alternative clay material for the engineered barrier in deep geological repositories. When combined with Eu3+ cations, they serve as an in situ luminescent probe for tracking the physical–chemical changes occurring in this engineered barrier over the long term. Therefore, a better understanding of the local environment of the lanthanide is highly desirable to comprehend the specific behavior of these systems. A combination of different techniques, (X-ray diffraction, thermogravimetry, fluorescence, and X-ray absorption spectroscopy), has allowed the study of the local environment of two luminescent lanthanide cations, Eu3+ and Gd3+, embedded in the galleries of two high-charge micas with different Si/Al tetrahedral ratio. The results show that the hydration state of these cations is primarily influenced by the layer charge of the aluminosilicate, and secondarily by the cation’s hydration enthalpy. High-charge micas doped with trivalent lanthanide cations are more hydrated compared to the original clays with Na+ in the interlayer. Nevertheless, both Eu3+ and Gd3+ are adsorbed as inner-sphere complexes in the galleries of high-charge micas. They are located inside the distorted hexagonal cavity in all cases, coordinated by 3 oxygens from the tetragonal sheet, one fluorine from the octahedral sheet, and by 2–4 oxygens from water molecules, all at distances around 2.4 Å. An additional oxygen atom at a distance of 3.45–3.50 Å, is proposed from an H2O molecule in the second coordination shell.
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Jan 2025
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