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This work conducts a review on the kinetics of the uranium and water reaction system by gathering all available kinetic data and across a wide range of reaction conditions. Temperature and pressure dependent kinetic equations that describe the reaction are derived for the uraniumwater vapour and uranium-liquid water systems. Detailed tables which provide information about the reaction conditions and other parameters for each rate point are constructed. From evaluation of the tables, the effects of underlying parameters on the reaction kinetics are discussed. It is suggested that these parameters contribute to the reported discrepancies between reaction rate values under similar conditions. Better prediction of the corrosion rate and rate behaviour can be achieved by combining the kinetic rate equations with the effect of these underlying parameters., (Copyright © 2020. Published by Elsevier B.V.)

A small scale sample nuclear waste package, consisting of a 28mm diameter uranium penny encased in grout, was imaged by absorption contrast radiography using a single pulse exposure from an X-ray source driven by a high-power laser. The Vulcan laser was used to deliver a focused pulse of photons to a tantalum foil, in order to generate a bright burst of highly penetrating X-rays (with energy >500keV), with a source size of <0.5mm. BAS-TR and BAS-SR image plates were used for image capture, alongside a newly developed Thalium doped Caesium Iodide scintillator-based detector coupled to CCD chips. The uranium penny was clearly resolved to sub-mm accuracy over a 30cm(2) scan area from a single shot acquisition. In addition, neutron generation was demonstrated in situ with the X-ray beam, with a single shot, thus demonstrating the potential for multi-modal criticality testing of waste materials. This feasibility study successfully demonstrated non-destructive radiography of encapsulated, high density, nuclear material. With recent developments of high-power laser systems, to 10Hz operation, a laser-driven multi-modal beamline for waste monitoring applications is envisioned., (Copyright © 2016. Published by Elsevier B.V.)

How do you characterise the contents of a sealed nuclear waste package without breaking it open? This question is important when the contained corrosion products are potentially reactive with air and radioactive. Synchrotron X-rays have been used to perform micro-scale in-situ observation and characterisation of uranium encapsulated in grout; a simulation for a typical intermediate level waste storage packet. X-ray tomography and X-ray powder diffraction generated both qualitative and quantitative data from a grout-encapsulated uranium sample before, and after, deliberately constrained H2 corrosion. Tomographic reconstructions provided a means of assessing the extent, rates and character of the corrosion reactions by comparing the relative densities between the materials and the volume of reaction products. The oxidation of uranium in grout was found to follow the anoxic U+H2O oxidation regime, and the pore network within the grout was observed to influence the growth of uranium hydride sites across the metal surface. Powder diffraction analysis identified the corrosion products as UO2 and UH3, and permitted measurement of corrosion-induced strain. Together, X-ray tomography and diffraction provide means of accurately determining the types and extent of uranium corrosion occurring, thereby offering a future tool for isolating and studying the reactions occurring in real full-scale waste package systems., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The photocatalytic reduction of carbon dioxide (CO(2)) on jet spray formed titanium dioxide (TiO(2)) was studied using light-emitting diode (LED) illumination centred at a wavelength of 388 nm. In addition, the photocatalytic reduction of CO(2) under soft X-ray irradiation was also studied. Specifically, the experiments examined the reduction of CO(2) in a gaseous and liquid-gas system using residual gas analysis mass spectrometry. A photochemical reduction of CO(2) was observed over a course of 250 min, with transformation to a major product, C(2)H(3)O(-) (ethenolate), until equilibrium was reached. The product was observed to be surface stabilised, with it reverting back to CO(2) over the course of 100 min without illumination. A proposed free radical mechanism is presented for the formation of this product. A similar effect to that of UV illumination is also observed to occur under the influence of soft X-rays, which presents a potentially significant alternative method for the activation of TiO(2)., (Copyright © 2011 Elsevier B.V. All rights reserved.)

For the past 15 years, nanoscale metallic iron (nZVI) has been investigated as a new tool for the treatment of contaminated water and soil. The technology has reached commercial status in many countries worldwide, however is yet to gain universal acceptance. This review summarises our contemporary knowledge of nZVI aqueous corrosion, manufacture and deployment, along with methods to enhance particle reactivity, stability and subsurface mobility. Reasons for a lack of universal acceptance are also explored. Key factors include: concerns over the long-term fate, transformation and ecotoxicity of nZVI in environmental systems and, a lack of comparable studies for different nZVI materials and deployment strategies. It is highlighted that few investigations to date have examined systems directly analogous to the chemistry, biology and architecture of the terrestrial environment. Such emerging studies have highlighted new concerns, including the prospect for remobilisation of heavy metals and radionuclides over extended periods. The fundamental importance of being able to accurately predict the long-term physical, chemical and biological fate of contaminated sites following nZVI treatment is emphasised and, as part of this, a universal empirical testing framework for nZVI is suggested., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The reaction between uranium and water vapour has been well investigated, however discrepancies exist between the described kinetic laws, pressure dependence of the reaction rate constant and activation energies. Here this problem is looked at by examining the influence of impurities in the form of carbide inclusions on the reaction. Samples of uranium containing 600 ppm carbon were analysed during and after exposure to water vapour at 19 mbar pressure, in an environmental scanning electron microscope (ESEM) system. After water exposure, samples were analysed using secondary ion mass spectrometry (SIMS), focused ion beam (FIB) imaging and sectioning and transmission electron microscopy (TEM) with X-ray diffraction (micro-XRD). The results of the current study indicate that carbide particles on the surface of uranium readily react with water vapour to form voluminous UO(3) · xH(2)O growths at rates significantly faster than that of the metal. The observation may also have implications for previous experimental studies of uranium-water interactions, where the presence of differing levels of undetected carbide may partly account for the discrepancies observed between datasets., (Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.)

Although contaminant removal from water using zero-valent iron nanoparticles (INP) has been investigated for a wide array of chemical pollutants, the majority of studies to date have only examined the reaction of INP in simple single-contaminant systems. Such systems fail to reproduce the complexity of environmental waters and consequently fail as environmental analogues due to numerous competitive reactions not being considered. Consequently there is a high demand for multi-elemental and site-specific studies to advance the design of INP treatment infrastructure. Here INP are investigated using batch reactor systems over a range of pH for the treatment of water containing multi-element contaminants specifically U, Cu, Cr and Mo, selected to provide site-specific analogues for leachants collected from the Lişava mine, near Oraviţa in South West Romania. Concurrently, a U-only solution was also analysed as a single-system for comparison. Results confirmed the suitability of nano-Fe(0) as a highly efficient reactive material for the aqueous removal of Cr(IV), Cu(II) and U(VI) over a range of pH applicable to environmental waters. Insufficient Mo(VI) removal was observed at pH >5.7, suggesting that further studies were necessary to successfully deploy INP for the treatment of geochemically complex mine water effluents. Results also indicated that uranium removal in the multi-element system was less than for the comparator containing only uranium., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Zero-valent iron nanoparticles (INP) were investigated as a remediation strategy for a uranium-contaminated waste effluent from AWE, Aldermaston. Nanoparticles were introduced to the effluent, under both oxic and anoxic conditions, and allowed to react for a 28-d period during which the liquid and nanoparticle solids were periodically sampled. Analysis of the solution indicated that under both conditions U was removed to <1.5% of its initial concentration within 1h of introduction and remained at similar concentrations until approximately 48 h. A rapid release of Fe into solution was also recorded during this initial period; attributed to the limited partial dissolution of the INP. XPS analyses of the reacted nanoparticulate solids between 1 and 48 h showed an increased Fe(III):Fe(II) ratio, consistent with the detection of iron oxidation products (akaganeite and magnetite) by XRD and FIB. XPS analysis also recorded uranium on the recovered particulates indicating the chemical reduction of U(VI) to U(IV) within 1h. Following the initial retention period U-dissolution of U was recorded from 48 h, and attributed to reoxidation. The efficient uptake and retention of U on the INP for periods up to 48 h provide proof that INP may be effectively used for the remediation of complex U-contaminated effluents., (Copyright 2010 Elsevier B.V. All rights reserved.)

In an attempt to characterize material intrinsic reactivity, iron dissolution from elemental iron materials (Fe(0)) was investigated under various experimental conditions in batch tests. Dissolution experiments were performed in a dilute solution of ethylenediaminetetraacetate (Na(2)-EDTA - 2mM). The dissolution kinetics of 18 Fe(0) materials were investigated. The effects of individual operational parameters were assessed using selected materials. The effects of available reactive sites [Fe(0) particle size (