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Abstract: The structural form and elemental distribution of material originating from different Fukushima Daiichi Nuclear Power Plant reactors (Units 1 and 3) is hereby examined to elucidate their contrasting release dynamics and the current in-reactor conditions to influence future decommissioning challenges. Complimentary computed X-ray absorption tomography and X-ray fluorescence data show that the two suites of Si-based material sourced from the different reactor Units have contrasting internal structure and compositional distribution. The known event and condition chronology correlate with the observed internal and external structures of the particulates examined, which suggest that Unit 1 ejecta material sustained a greater degree of melting than that likely derived from reactor Unit 3. In particular, we attribute the near-spherical shape of Unit 1 ejecta and their internal voids to there being sufficient time for surface tension to round these objects before the hot (and so relatively low viscosity) silicate melt cooled to form glass. In contrast, a more complex internal form associated with the sub-mm particulates invoked to originate from Unit 3 suggest a lower peak temperature, over a longer duration. Using volcanic analogues, we consider the structural form of this material and how it relates to its environmental particulate stability and the bulk removal of residual materials from the damaged reactors. We conclude that the brittle and angular Unit 3 particulate are more susceptible to further fragmentation and particulate generation hazard than the round, higher-strength, more homogenous Unit 1 material.

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Abstract: Pitting corrosion of iron has been studied via artificial pits. Solid corrosion products have been observed in the pit solution, which have been characterised as disordered carbon and Fe 3 C (known as both cementite and cohenite) using in - situ synchrotr on XRD and ex - situ Raman spectroscopy. These corrosion products were found to act as diffusion barriers for metal ions and to give a small increase in the solution resistance. The formation of carbon - containing corrosion products depends upon the interfaci al potential. The potential dependence suggests that Fe 3 C may be protected from dissolution by a carbon layer. High purity iron was used to calculate an effective diffusion coefficient for metal ions (a combination of self - diffusion and electrical migratio n) in different MgCl 2 concentrations during diffusion - limited dissolution. The contribution of self - diffusion increases with increasing MgCl 2 concentration if the depletion of Mg 2+ in the pit is considered. The Tafel kinetics of iron dissolution in solutio ns saturated in Fe 2+ has been studied in different MgCl 2 concentrations . The Tafel slope (56 to 70 mV/decade) was independent of MgCl 2 and FeCl 2 concentration when FeCl 2 is saturated. The effect of nitrate on the composition and structure of salt layers ha s been characterised using in - situ synchrotron XRD. The salt layer has been found to be composed of FeCl 2 .4H 2 O in chloride with and without trace nitrate, and Fe(NO 3 ) 2 .6H 2 O in nitrate with trace chloride. The salt layer is isotropic in HCl and anisotropic in HCl with trace nitrate. The dissolution behaviour of iron in HCl and chloride/nitrate solutions has been studied using in - situ synchrotron X - ray radiography. It has been found that dissolution is relatively uniform in the presence of salt layers, but cr evice formation and surface roughening can take place on salt - free surfaces. The potentiodynamic measurements on iron in nitrate/chloride solutions induce abrupt transitions between dissolution and passivation, resulti ng in deep and localised attack .

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Abstract: Synchrotron based ?-XRF, ?-XAS and ?-XRD have made a major impact in the field of environmental science in the last ten years. One of the first seven ‘day one’ beamlines on the Diamond Light Source is a microfocus spectroscopy beamline, beamline I18. Here the current status of the beamline and the opportunities it presents in the field of environmental science are described, with results from two of the first experiments also included. The first is based on the use of bonemeal to remediate soil. We used Zn K-edge and Pb L3-edge spectroscopy to characterize the speciation of these two elements on a soil after bonemeal treatment. The results are compared with bulk measurements taken on the whole soil and standard materials. The second experiment described here is a study of the speciation and association of Ni in a laterite from Moa Bay, Cuba. Here the differences in the Ni speciation associated with Mn oxides are examined and compared with Fe oxides phases.

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Abstract: We present Ba L3-X-ray Absorption Fine Structure (XAFS) data from a suite of barium carbonates (witherite, alstonite, barytocalcite), hydroxides, sulfate(vi) (barite) and a Ba-bearing organic compound to explore whether Ba L3-XAFS could be used to fingerprint structural states in biominerals such as celestite, aragonite and calcite. Although there is a general similarity between all X-ray Absorption Near Edge Structure (XANES), subtle differences are observed in detail, which allow almost all phases to be distinguished. The XANES are considered as composites of four components, termed ‘A’ (5255 eV), ‘B’ (5258 eV), ‘C’ (5268 eV) and ‘D’ (5273 eV). ‘A’ is observed in barium hydroxides and most visible in the first derivatives of the XANES data. The minimum after the Ba L3 white line lies at 5257 eV for most materials but higher (5261 eV) for barium hydroxides due to the influence of the ‘A’ component. ‘B’ is present in aragonite-group minerals (witherite and alstonite) and may be a fingerprint of that structural state. ‘C’ and ‘D’ overlap and form a board hump at ∼ 5270 eV, but the relative proportions of ‘C’ and ‘D’ are variable between phases and are to some degree diagnostic. Refinement of Extended X-ray Absorption Fine Structure (EXAFS) allows estimates of first shell (Ba–O) bond distances in all materials, which are within 4% of average distances estimated from diffraction studies. Subsequent shells (Ba–S for barite; Ba–metal in witherite, alstonite and barytocalcite) can be resolved. The state of Ba:Ca order in alstonite and barytocalcite is successfully modelled and both are found to be fully ordered. The significant static disorder in Ba-bearing minerals is accommodated successfully by large Debye–Waller values in the refinements. Combinations of XANES and EXAFS allow all phases to be identified, with the exception that the two hydrated barium hydroxides cannot be distinguished from each other. The XANES of a celestite (SrSO4 containing ∼ 100 ppm Ba) is comparable to the barite spectra after only seven cycles (collected over < 5 h), showing that XANES can be resolved in samples with low Ba concentrations. However we were unable to analyse successfully an aragonitic Porites coral skeleton (containing ∼ 3–4 ppm Ba) using the current instrumentation due to the proximity in energy of Ca Kα secondary X-radiation to the Ba Lα energy and which overloaded the X-ray detector. The use of multilayer crystal detectors will be required to resolve the Ba Lα energy in calcium carbonate samples containing low Ba concentrations. Alternatively Ba EXAFS may be accessible through the Ba K edge.