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Abstract: Recent studies apparently finding deleterious effects of radiation exposure on cataract formation in birds and voles living near Chernobyl represent a major challenge to current radiation protection regulations. This study conducted an integrated assessment of radiation exposure on cataractogenesis using the most advanced technologies available to assess the cataract status of lenses extracted from fish caught at both Chernobyl in Ukraine and Fukushima in Japan. It was hypothesised that these novel data would reveal positive correlations between radiation dose and early indicators of cataract formation. The structure, function and optical properties of lenses were analysed from atomic to millimetre length scales. We measured the short-range order of the lens crystallin proteins using Small Angle X-Ray Scattering (SAXS) at both the SPring-8 and DIAMOND synchrotrons, the profile of the graded refractive index generated by these proteins, the epithelial cell density and organisation and finally the focal length of each lens. The results showed no evidence of a difference between the focal length, the epithelial cell densities, the refractive indices, the interference functions and the short-range order of crystallin proteins (X-ray diffraction patterns) in lens from fish exposed to different radiation doses. It could be argued that animals in the natural environment which developed cataract would be more likely, for example, to suffer predation leading to survivor bias. But the cross-length scale study presented here, by evaluating small scale molecular and cellular changes in the lens (pre-cataract formation) significantly mitigates against this issue.

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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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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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Abstract: Crystal chemical design principles were applied to synthesise novel U4+ dominant and titanium excess betafite phases Ca1.15(5)U0.56(4)Zr0.17(2)Ti2.19(2)O7 and Ca1.10(4)U0.68(4)Zr0.15(3)Ti2.12(2)O7, in high yield (85–95 wt%), and ceramic density reaching 99% of theoretical. Substitution of Ti on the A-site of the pyrochlore structure, in excess of full B-site occupancy, enabled the radius ratio (rA/rB = 1.69) to be tuned into the pyrochlore stability field, approximately 1.48 ≲ rA/rB ≲ 1.78, in contrast to the archetype composition CaUTi2O7 (rA/rB = 1.75). U L3-edge XANES and U 4f7/2 and U 4f5/2 XPS data evidenced U4+ as the dominant speciation, consistent with the determined chemical compositions. The new betafite phases, and further analysis reported herein, point to a wider family of actinide betafite pyrochlores that could be stabilised by application of the underlying crystal chemical principle applied here.

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Abstract: Composites of sodium-exchanged zeolite chabazite particles with attached superparamagnetic nanoparticles of Fe3O4 and CoFe2O4 ferrite spinels have been produced using a novel solvothermal route. These have been characterized by a combination of techniques, including powder x-ray diffraction, x-ray fluorescence spectroscopy, vibrating sample magnetometry, and both scanning and transmission electron microscopy. These confirm the nature of the attached nanoparticles, and the microscope images show a good dispersion of nanoparticles with a narrow size range deposited uniformly on the surface of the zeolite particles. The magnetization is of sufficient strength to allow magnetic separation from a solution. Both time and pH dependent Cs uptake experiments show that the magnetized systems are still excellent for the rapid uptake of Cs via an ion exchange process with no reduction in property due to the attached nanoparticles.