The calculation of dry particle deposition velocity (Vg) for small particles in field studies is subject to much variability between theoretical and measured values. This work will assess some of the factors which may influence the calculation of Vg. The other key parameter which is used to define the near-surface exchange of material is the resuspension factor (K). The certainty of using a Vg which is representative of small particles typically 1 pm requires clarification. During September 1993-1994, four size-selective air and deposition experiments were carried out at an on-site and off-site sampling location close to the BNFL Sellafield nuclear reprocessing plant in Cumbria UK. Dry and total (wet & dry) particle deposition velocities were determined for ^^^Cs, The dry deposition velocities of naturally-occurring ^Be were also determined and used as a 'marker' for small particle transport processes. Resuspension factors K (m ^) for radiocaesium and Plutonium were also derived. Automated individual particle characterisation (AlP) using scanning electron microscopy coupled to energy-dispersive x-ray analysis (SEM-EDXA) was used to determine the particle size distribution and associated elemental composition of material deposited to Frisbee deposition collectors. Enhanced a-emitting hot-spots from surface soils and material deposited to Frisbee collectors at 1 m above ground level were isolated and characterised for size and shape using nuclear track detector film, LR-115. Dry particle deposition velocities for ^^^Cs, 239+240py and were commonly in excess of 1E-03 m s"^ by more than two orders of magnitude. Total deposition velocities (dry and wet) were even higher with values ranging from 0.2 m s^ -1 ms"^ for both radiocaesium and plutonium. High derived values of dry deposition velocity for radiocaesium and plutonium were to some extent influenced by air sampling artefacts. Air sampling artefacts result in an under-estimation of airborne activity for radioactivity associated with particle diameters >10 pm. The derived values of dry particle deposition velocity for ^Be were consistent with literature values of sub-micron sized particles with evidence of a seasonal spring maximum. Resuspension factors K (m'^) for radiocaesium and plutonium agreed well with literature values of weathered weapons fallout values which ranged from 2E-08 to 5E-11 (m"^) for plutonium and radiocaesium respectively. Differences in dry particle deposition velocities for radiocaesium and plutonium between the on-site and off-site locations varied by no more than a factor of three. Correlations between dry particle deposition velocities for Cs and Pu with wind speed, wind direction and precipitation rates were not found. Size-specific air sampling show that the majority of the plutonium was predominantly associated with the >11 lam aerosol size fraction. The association between activity and large particle size suggest this material was probably attached to large soil-derived particles. Plutonium isotope data indicate this material originated fromthe nuclear weapons programme of the late 1950's-earty 1970's. Radiocaesiumactivities were equally distributed between the < 10 ixm and > 11 ^m aerosol fractions for two out of the four runs. This suggests that historically deposited ''^^Cs and current emissions contributed to measured airborne activities. Enhanced a-emitting hot-spots were isolated from bulk surface soils and in material deposited to Frisbee collectors. Rare particles such as these with atypical activities of Pu may lead to mis-leadingly high deposition fluxes. The calculation of Vg in the field is therefore sensitive to the presence of these particles because they are not representative of the aerosol flux and their size s 50 |im precludes their collection by the Pmio air sampler. The main conclusions of this work indicates the very high values of Vg sometimes measured in the field are strongly influenced by large resuspended soil particles and associated air sampling artefacts. The inclusion of large particles within the deposition flux is confirmed by size selective mass based Vg using scanning electron microscopy

No description available.

The mechanisms controlling radiocaesium migration through the peat soil were investigated by considering physico-chemical & biological factors affecting radionuclide adsorption/desorption in the peat soil using the Batch & Column Methods as well as a "Direct Fumigation Extraction Method". The biological factors were investigated under different conditions by variation of the micro-organisms content in the peat soil, the soil solution and leaching conditions. Samples of peat soil were reacted with solutions containing caesium ions, and the effect on caesium-K_d determined. The caesium adsorption/desorption was found to be influenced by concentration of caesium and other cations (NH₄⁺, K⁺ and Ca⁺⁺) and by the pH of the solution. Below pH 3, in presence of calcium and potassium, desorption could occur as the exchangeable sites on microparticles were replaced by other cations. At pH>1, in presence of ammonium, adsorption could occur. The distribution coefficient, K_d value was strongly reduced following the addition of NH₄⁺, K⁺ and Ca⁺⁺ at a fixed pH. NH₄⁺ was found to be more effective in the caesium desorption than the other cations. By increasing the concentration of radiocaesium (>0.2 MBq/100μl) the effect became much less leading eventually to an increase in caesium-K_d values. A decrease in the caesium-K_d was also observed at pH<3 in peat samples. It was found that the caesium adsorption approached to an equilibrium state at pH>3 depending upon caesium concentration in peat solution. Caesium adsorption took 180 days to reach equilibrium state. For the measurement of the release/uptake of radionuclides in the peat soils by the microbial biomass, homogenised wet peat samples were fumigated by chloroform. The influence of the microbial population present in the peat on the environmental mobility of caesium was clearly demonstrated.

The complexity of cementitious matrices and their application in the immobilisation of radioactive waste has led to detailed examination of their ability to condition permeating water to high pH by both experimental and thermodynamic studies. This thesis considers the stability and solubility of pure hydrate phases: Ca(OH)₂; CaO-SiO₂-H₂O gel, Ca:Si = 0.85, 1.1, 1.4, 1.8; 3CaO.Al₂O₃.6H_zO; 3CaO.Al₂O₃.CaSO₄.12H₂O and 3CaO.Al₂O₃.3CaSO₄.32H₂O, and the phase formation and stability within CaO-SiO₂-CaCO₃-H₂O and CaO-Al₂O₃-SiO₂-H₂O compositions aged in saline solutions, up to 1.5M NaCl and 0.05M MgSo₄, at 25°, 55° and 85°C. The two main high pH conditioning phases of cementitious systems are Ca(OH)₂ and C-S-H gel. Sodium chloride enhances the solubility of Ca(OH)₂ and causes a slight reduction in the Ca:Si ratio of C-S-H gels by the progressive leaching of calcium. Silicate polymerisation within C-S-H phases is inhibited by sodium chloride though it is uncertain how this alters the crystallisation kinetics. The pH buffering capacity is maintained when aged in sodium chloride concentrations 0.5, 1.0 and 1.5M at 25°, 55° and 85°C. The stability of calcium sulfoaluminate aged in sodium chloride is greater than of 3CaO.Al₂O₃.6H₂O, which is unstable with respect to 3CaO.Al₂O₃.CaCl₂.10H₂O in NaCl < 0.5M. These phases undergo a progressive phase change to the 3CaO.Al₂O₃.0.5CaSO₄.0.5CaCl₂.10-12H₂O and 3CaO.Al₂O₃.CaCl₂.10H₂O at increasing aqueous Cl:SO₄ ratios. The formation of a limited solid solution region within 3CaO.Al₂O₃.xCaSO₄.l-xCaCl₂.yH₂O: 0.00 ≤ SO₄:Cl ≤ 0.06, was characterised. In magnesium sulfate, 5 - 50m.mol/l, calcium within hydrate phases is progressively replaced by magnesium with formation of Mg(OH)₂, MgO-SiO₂-H₂O gel, 4MgO.Al₂O₃.xH₂O and gypsum. The pH conditioned by the resultant solid assembly decreases to less than that desirable for containment of radioactive waste, to < 9. Consideration of the phase formation and persistence within the CaO-SiO₂-CaCO₃-H₂O and CaO-Al₂O₃-SiO₂-H₂O systems was examined in solutions containing both sodium chloride and magnesium sulfate. The chemical interactions observed were dominated by the replacement of calcium by magnesium within the solid phases with the formation and persistence of mixtures of Mg(OH)₂, MgO-SiO₂-H₂O gel and gypsum. At low Mg:Ca-CO₃ ratios the persistent stability of gehlenite hydrate at 25°C was observed in appropriate samples. The chemistry of the aqueous phase is dependent on the Mg:Ca-CaCO₃ ratio as well as the Ca:Si ratio. At high Mg:Ca-CaCO₃ ratios the high pH conditioning properties are destroyed and buffering occurs at a value below pH 9.

The current work proposes a novel approach to the production of sorbent materials, which integrates recycling of calcium silicate-based industrial residues and sequestration of carbon dioxide in the process of accelerated carbonation. The concept was tested on model substrates of suitable mineralogy, namely Portland cement and dicalcium silicate, which were carbonated, and examined by nitrogen adsorption, XRD, NMR, SEM, TG-DTA analytical techniques. The carbonated materials were evaluated in batch sorption studies with the solutions of cadmium, lead, nickel, cobalt, zinc, strontium and cesium. The findings of the structural examination indicated the transformation of nesosilicate-type calcium silicates during carbonation into polymerized Ca-silicate frameworks, aragonite (in carbonated cement only) and calcite. The NMR investigation, for the first time, described in detail the nature of polymerized silicates (predominantly Q3 and Q4 silicon environment) in carbonated cement and dicalcium silicate. The carbon dioxide uptake measured by thermogravimetric analysis was equivalent to 480 kg/t and 370 kg/t of CO2 reacted with dicalcium silicate and Portland cement, respectively. Batch sorption experiments demonstrated better metal removal efficiencies by carbonated cement, particularly for cadmium and cesium. It was concluded that the metal removal mechanisms ranged from adsorption (e.g. ion-exchange, complexation, isomorphic substitution) to surface and bulk precipitation. The main solubility-limiting phases identified for cadmium, lead, strontium and zinc were otavite CdCO3 (only detected in carbonated cement), (hydro-)cerussite, strontianite, and hydrozincite. Cobalt, nickel, cesium were selectively sorbed within the Si-rich phase of both carbonated cement and dicalcium silicate. The leach study demonstrated an adequate containment of sorbed/precipitated metals within carbonated cement (= 2.5% leached) and carbonated dicalcium silicate (= 12% leached) in water. Metal mobility, however, increased during the exposure to acidic conditions, with = 5% of cadmium, lead, cobalt, nickel and 15- 75% of zinc, cesium, strontium being mobilized into leachates.

No description available.

This research presents the development of CityZoom UP, the first attempt to extend existing urban planning software in order to assist in modelling urban scenarios and setting up simulation parameters for Gaussian dispersion and CFD models. Based on the previous capabilities and graphic user interfaces of CityZoom to model and validate urban scenarios based on Master Plan regulations, new graphic user interfaces, automatic mesh generation and data conversion algorithms have been created to seamlessly generate input data for dispersion model AERMOD and CFD packages CFX and OpenFOAM. A key feature of CityZoom UP is the introduction of vehicular pollution source parameters in dispersion and CFD models, allowing the urban designer to assess the local impact of adding or modifying a building or group of buildings on the street air quality. Traffic emissions are modelled as sequence of point sources. CityZoom UP uses Atmospheric Dispersion model AERMOD to assess the dispersion of pollutants in large scale urban environments for strategic planning, quickly providing results for different alternatives of urban scenarios, meteorological and traffic profiles. Sensitivity and validation tests are performed and the results are compared to wind tunnel and real world tracer experiments from the DAPPLE campaign. For the first time in the available literature AERMOD is used to perform dispersion simulation using tracer emission data from mobile vehicular sources in a complex urban scenario, considering building wake effects. CityZoom UP also provides automated 3D meshing, including mesh refinement, identification of physical boundaries in the mesh, and automatic setup of CFD simulations of urban scenarios, for the detailed calculation of air flow and dispersion of pollutants in specific areas inserted in urban environments. These capabilities can greatly reduces the time necessary for the setup CFD cases, even if it does not affect the computational time needed to run the CFD simulations. Tests show how CityZoom UP can be used to model alternative scenarios for a given location, e.g. present situation and future scenario including a new tall building, and to easily automate the generation of different meshes for each scenario, based on boundary layer and size function refinement parameters. The present and possible future situations of a real world scenario in Porto Alegre are modelled as a show case for CityZoom UP. The capabilities to assist in modelling alternative urban scenarios and setting up AERMOD and CFD simulations based on those scenarios is demonstrated.

Changes in the atmospheric concentration of greenhouse gases and aerosols alter the energy balance of the climate system. CO2 is the most significant anthropogenic greenhouse gas. The primary source of the increased atmospheric concentration of CO2 since the preindustrial period is from fossil fuel exploitation. As the global need for energy is currently met by combustion of fossil fuels it is imperative that a method of reducing the levels of CO2 being emitted is used. Carbon capture and storage (CCS) is the combination of CO2 capture from large point sources, with the transport of CO2 to a suitable geological storage site where it can safely be contained. Geological CCS technology has the potential to a make a significant contribution to a low carbon technology future. As with any technology, it is imperative to identify techniques that could be used to form part of the monitoring programme. In this thesis, the role of chemical and geochemical tracers are investigated during the transport and storage of CO2. For the first part of this research, a review of the natural gas and CO2 pipeline network in North America and United Kingdom has been compiled from published literature and historical experience. Using this information, research was carried out to determine why odourising has been suggested for CO2 pipeline transport and what benefit it would add. Based on experience from natural gas, it is concluded that high pressure pipelines of CO2 through sparsely populated areas could have odourant added, but will gain little safety benefit. However, adding odourant to CO2 gas phase pipes could aid detection of leaks as well improve public assurance and should be considered in more detail. For the second part of this research, a specially constructed flow cell was designed and built to investigate how noble gases could be used as effective early warning tracers for CO2 migration in storage sites. From this equipment, experimental breakthrough curves for noble gases and SF6 travelling through a sample of Fell sandstone in relation to CO2 over a pressure gradient range of 10,000 – 50,000 Pa were generated. Although noble gases are described as conservative tracers, comparing the breakthrough curves over a range of pressure gradients show that they do not behave as simply as previously assumed. These results were then modelled using a one dimensional advective dispersion transport equation to fit curves to the experimental outputs using two different modelling approaches. A statistical approach can derive the input parameters for an analytical approach, which is needed to understand the dispersivity behaviour of the tracers. A set of values for the dispersivity of noble gases, SF6 and CO2 through porous media is presented in this research. Using a baseline value approach, initial arrival times for krypton and xenon from this research suggest that they could be used as a means of detecting CO2 migration. While helium, neon and argon appear to be unsuitable as early warning tracers for initial detection of CO2, this suggests that they can be used as part of mixture to fingerprint individual CO2 storage sites that may be in close proximity to one another. Results from the experimental and modelling analysis, identify a system where preferential paths exist depending on the change in pressure gradient. The different transport channels progress from a Darcy linear flow regime to a non-linear laminar flow. These results propose an explanation for the patterns observed from tracers in large-scale reservoirs but the output values obtained are limited by scale-dependence and would not be suitable for direct upscaling.

This thesis presents a comprehensive investigation into the underlying coupled processes in coal in response to high pressure gas injection. This is achieved by i) developing a new high pressure gas experimental facility and conducting a series of experimental tests, and ii) developing and applying a theoretical and numerical model. A novel experimental facility was designed, which offers stable and continuous high-pressure injection of gases in fractured rocks, for detailed study of the reactive transport processes. It consists of the gas supply and backpressure control system. Using the newly developed experimental facility, the response of coal subject to subcritical and supercritical gas injection under stable and variable temperature conditions was studied. The experimental investigation consisted of a series of tests: i) sorption capacity and kinetics tests, ii) uniaxial compressive tests, iii) sieve analysis tests, iv) flow and deformation tests. Thirty anthracite coal samples from different depths (i.e. 150 m and 550 m) and locations from the South Wales coalfield were characterised and tested. The capabilities of the theoretical and numerical modelling platform of thermal, hydraulic, chemical and mechanical processes were advanced. A new theoretical approach was adopted which successfully incorporates reactive gas transport coupled with coal deformation. The development of constitutive relationships describing the sorption induced elastic isotropic swelling of coal and changes in permeability was considered in detail. Numerical solutions of the governing flow and deformation equations were achieved by employing the finite element method for spatial discretisation and the finite difference method for temporal discretisation. The new model was verified for its accuracy via a series of benchmark tests and validated using high-resolution experimental data. The results of the experimental study showed that the sorption capacity and kinetics are sample-size dependent, particularly for deeper coal. Higher and faster sorption of CO2 obtained on powdered samples compared to intact samples indicated that sorption processes are governed by fracture interconnectivity and accessibility of pores. Sorption of CO2 was found to significantly reduce the brittleness, uniaxial compressive strength and elastic modulus of anthracite coals. The results of the post-failure sieve analysis showed that CO2 saturated samples disintegrated on smaller particles than non-saturated samples indicating that sorption induced swelling weakens the coal structure by enhancing the existing and inducing new fractures. During CO2 flow through coal under constant stress, samples experienced swelling resulting in initial reduction followed by recovery of measured flow rates. CO2 sorption induced changes were found to be non-reversible. The results of high CO2 flow through coal showed that CO2 reduced the temperature of the system, associated with Joule- Thomson cooling, enhancing the coal swelling and opposite to expected, increasing the flow rates. Overall, the high-resolution data-set obtained is a significant contribution to the scientific community and is able to provide a means of validation for future models. The results of the verification and validation exercises demonstrated the capability of the developed model to simulate coupled processes involved in gas transport in coal. A series of numerical simulations were conducted to investigate the permeability evolution and CO2 breakthrough in coal subject to supercritical CO2 injection using the developed model. Different scenarios were considered, involving a range of values of the elastic modulus and the parameter defining the coal swelling. The results of the advanced numerical simulations showed that the effect of CO2 sorption induced swelling on permeability reduces with a decrease in coal stiffness suggesting that CO2 sorption induced reduction of elastic modulus would have a positive effect on the ability of coal to conduct CO2. In this work, confidence in the feasibility of CO2 storage in anthracite coals was improved by enhancing the knowledge of high pressure gas-coal interactions through both experimental and numerical investigations. Moreover, it is claimed that newly developed model enables predictions of coupled processes involved in carbon sequestration in coal.

The use of active carbon (AC) as a potential adsorbent for the removal of uranium from aqueous solution has been investigated. Two principal areas have been studied i.e. uranium adsorption from near-neutral and dilute acidic solutions and uranium adsorption from concentrated acid solutions. The aqueous solution matrix used was nitric acid. In the former case commercial (as-received) and oxidized active carbons were investigated. It was noticed that oxidation of as-received ACs with nitric acid solution significantly improves the adsorption capacity of uranium from both near-neutral and dilute acidic solutions. Oxidized ACs were particularly effective in dilute acidic solution , whilst as-received ACs have shown little uranium sorption. Batch equilibrium isotherms were constructed to compare the adsorption capacities of as-received and oxidized ACs. The batch kinetics of uranium adsorption was studied and a column experiment was performed.