No description available.

This work focuses on diffusion and advection through cementitious media, the work arises from two research contracts undertaken at Loughborough University: Experiments to Demonstrate Chemical Containment funded by UK NDA and the SKIN project, funded by the European Atomic Energy Community's Seventh Framework Programme. Diffusion will be one of the most significant mechanisms controlling any radionuclide migration from a nuclear waste, deep geological disposal facility. Advection may also occur, particularly as the immediate post closure groundwater rebound and equilibration proceeds but is expected to be limited by effective siting and management during the operational phase of the facility. In this work advection is investigated at laboratory scale as a possible shorter timescale technique for providing insight into the much slower process of diffusion. Radial techniques for diffusion and advection have been developed and the developmental process is presented in some detail. Both techniques use a cylindrical sample geometry that allows the radionuclide of interest to be introduced into a core drilled through the centre of the test material. For diffusion the core is sealed and submerged in a container of receiving solution which is sampled and analysed as the radionuclide diffuses into it. For advection, a cell has been designed that allows inflow via the central core to pass through the sample in a radial manner and be collected as it exits from the outer surface. The radionuclide of interest can be injected directly into the central core without significant disturbance to the advective flow. Minor improvements continue to be made but both techniques have provided good quality, reproducible results. The majority of the work is concentrated on a potential cemetitious backfill known as NRVB (Nirex Reference Vault Backfill) this is a high porosity, high calcium carbonate content cementitious material. The radioisotopes used in this work are 3H (in tritiated water), 137Cs, 125I, 90Sr, 45Ca, 63Ni, 152Eu, 241Am along with U and Th salts. In addition the effect of cellulose degradation products (CDP) on radioisotope mobility was investigated by manufacturing solutions where paper tissues were degraded in water, at 80°C, in the absence of air and at high pH due to the presence of the components of NRVB. All diffusion experiments were carried out under a nitrogen atmosphere. All advection experiments were undertaken using an eluent reservoir pressurised with nitrogen where the system remained closed up to the point of final sample collection. Results for tritiated water and the monovalent ions of Cs and I were produced on a timescale of weeks to months for both diffusion and advection. The divalent ions of Sr, Ca and Ni produced results on a timescale of months to years. Variations of the experiments were undertaken using the CDP solutions. The effects of CDP were much more apparent at radiotracer concentration than the much higher radiotracer with non-active carrier, concentration. In the presence of CDP Cs, I and Ni were found to migrate more quickly; Sr and Ca were found to migrate more slowly. Additional Sr experiments were undertaken at elevated ionic strength to evaluate the effect of the higher dissolved solids content of the CDP solutions. Some of the results for HTO, Cs, I and Sr have been modelled using a simple numerical representation of the system in GoldSim to estimate effective diffusivity and partition coefficient. The diffusion model successfully produced outputs that were comparable to literature values. The advection model is not yet producing good matches with the observed data but it continues to be developed and more processes will be added as new results become available. Autoradiography has been used to visualise the radionuclide migration and several images are reproduced that show the fate of the radiotracers retained on the NRVB at the end of the experiments. As the experimental programme progressed it was clear that results could not be produced in a suitable timescale for Eu, Am U and Th. These experiments have been retained and will be monitored every six months until either diffusion is detected or the volume of receiving liquid is inadequate to ensure the NRVB is saturated.

Philosophiae Doctor - PhD / In Africa as well as in the world, South Africa plays an important role in the mining industry which dates back almost 120 years. Mining activities in South Africa mainly take place in Gauteng Province. Every year millions of tons of rocks are taken from underground, milled and processed to extract gold. Uranium is one of the minerals which is mined as a by-product of gold. The uranium bearing tailings are then placed on large dumps which are usually one or more kilometres in diameter in the environment. There are approximately 250 gold mine tailings dumps covering a total area of about 7000 ha. These gold mine tailings dumps contain considerable amounts of radium (226Ra) and have therefore been identified as large sources of radon (222Rn). Radon release from these tailings dumps pose health concerns for the surrounding communities. This study reports on the 222Rn soil-gas concentrations and exhalations measurements which were conducted at a non-operational mine dump (Kloof) which belongs to Carletonville Gold Field, Witwatersrand, South Africa. Radon soil-gas concentrations were measured using a continuous radon monitor (the Durridge RAD7). The radon soil gas concentration levels were measured at depths starting from 30 cm below ground/air interface up to 110 cm at intervals of 20 cm. These radon soil-gas measurements were performed at five different spots on the mine dump. The concentrations recorded ranged from to kBq.m-3. Furthermore, thirty four soil samples were taken from these spots for laboratory-based measurement. The soil samples were collected in the depth range 0-30 cm and measured using the low-background Hyper Pure Germanium (HPGe) -ray detector available at the Environmental Radioactivity Laboratory (ERL), iThemba LABS, Western Cape Province. The weighted average activity concentrations in the soils samples were Bq.kg-1, Bq.kg-1 and Bq.kg-1 for 238U, 40K and 232Th, respectively. 1 26 23 472 7 308 5 2551 18 The activity concentration of 40K and the decay series of 238U and 232Th for the top 30 cm of the accessible parts of the mine dump were measured using the MEDUSA (Multi-Element Detector for Underwater Sediment Activity) -ray detection system which was mounted on the front of a 44 vehicle, 0.6 m off the ground. The spectra acquired by the MEDUSA system were analysed and the activity concentrations were extracted using the Full Spectrum Analysis approach. The average activity concentrations obtained were 25975 Bq.kg-1 for 40K, 30940 Bq.kg-1 for 238U series and 185Bq.kg-1 for 232Th series for 2002 survey while 26075 Bq.kg-1 for 40K, 31040 Bq.kg-1 for 238U series and 20 5 Bq.kg-1 for 232Th series were recorded for 2010 survey. Moreover, a novel technique by means of the MEDUSA -ray detection system was utilised to map radon exhalation from the Kloof mine dump. In this technique the 214Bi concentration in the top 30 cm of the dump, which is used as a proxy for the 238U or 226Ra concentration, is measured even though there is not secular equilibrium between the radium and bismuth because radon has escaped. The actual activity concentrations of 40K and 226Ra are obtained from soil samples which were collected, sealed and measured in the laboratory settings after attaining secular equilibrium since radon gas does not escape. By comparing the ratios of the activity concentrations of the 214Bi obtained in the field using the MEDUSA -ray detector system to the activity concentrations of the 214Bi obtained in the laboratory using the HPGe -ray detector system yields a reasonable radon exhalation for a particular location in the mine dump. In this case it is assumed that the 40K and 232Th series activity concentrations are not or hardly affected by radon exhalation. By applying this new technique an average normalised radon flux of 0.120.02 and 0.120.02 Bq.m-2.s-1 were obtained for 2002 and 2010 surveys, respectively. The electrets and the IAEA standard formula were also utilised to calculated radon fluxes yielding 0.060.02 and 0.120.02 Bq.m-2.s-1 respectively.

No description available.

Centrosomin (Cnn) is an integral centrosomal protein in Drosophila with orthologues in several species, including humans. The human orthologue of Cnn is required for brain development with Cnn hypothesised to play a similar role in Drosophila. Control of Cnn incorporation into centrosomes is crucial for controlling asymmetric division in certain types of Drosophila stem cells. FRAP experiments on Cnn show that Cnn recovers in a pe- culiar fashion, which suggest that Cnn may be incorporated closest to the centrioles and then spread radially outward, either diffusively or ad- vectively. The aim of this thesis is to understand the mechanism of Cnn incorporation into the Drosophila centrosomes, to determine the mode of transport of the incorporated Cnn, and to obtain parameter estimates for transport and biochemical reactions. A crucial unknown in the modelling process is the distribution of Cnn receptors. We begin by constructing coupled partial differential equation models with either diffusion or advection as the mechanism for incorpo- rated Cnn transport. The simplest receptor distribution we begin with involves a spherical, infinitesimally thick, impermeable shell. We refine the diffusion models using the insights gained from comparing the model out- put with data (gathered during mitosis) and through careful assessment of the behaviour of the data. We show that a Gaussian receptor distribution is necessary to explain the Cnn FRAP data and that the data cannot be explained by other simpler receptor distributions. We predict the exact form of the receptor distribution through data fitting and present pre- liminary experimental results from our collaborators that suggest that a protein called DSpd2 may show a matching distribution. Not only does this provide strong experimental support for a key prediction from our model, but it also suggests that DSpd2 acts as a Cnn receptor. We also show using the mitosis FRAP data that Cnn does not exhibit appreciable radial movement during mitosis, which precludes the use of these data to distinguish between diffusive and advective transport of Cnn. We use long time Cnn FRAP data gathered during S-phase for this purpose. We fit the S-phase FRAP data using the DSpd2 profiles gath- ered for time points corresponding to the Cnn FRAP experiments. We also use data from FRAP experiments where colchicine is injected into the embryos to destroy microtubules (since microtubules are suspected to play a role in advective transport of Cnn). From the analysis of all these data we show that Cnn is transported in part by advection and in part by diffusion. Thus, we are able to provide the first mechanistic description of the Cnn incorporation process. Further, we estimate parameters from the model fitting and predict how some of the parameters may be altered as nuclei progress from S-phase to mitosis. We also generate testable predic- tions regarding the control of the Cnn incorporation process. We believe that this work will be useful to understand the role of Cnn incorporation in centrosome function, particularly in asymmetrically dividing stem cells.

No description available.

No description available.

No description available.

Pour mieux appréhender les mécanismes de transfert des gaz (CO2 et CH4) dissous dans l’eau porale des formations des marnes du site de Bure et des argiles à Opalinus (AOP) du Mt Terri dans leur état initial, un capteur infrarouge (IRTF) et un banc optique Raman innovant ont été développés et installés en laboratoire souterrain. Ces capteurs sont intégrés au dispositif de l’expérimentation « d’équilibration de gaz » développée par l’Andra (PAC) qui vise à suivre l’évolution d’une phase gazeuse initialement neutre au contact de la formation et de son eau porale grâce à un forage effectué et maintenu dans des conditions anaérobiques. Ces capteurs permettent un suivi quantitatif in situ et en ligne des gaz libérés par la formation à basse pression totale (<1,3 bar). Les modèles quantitatifs développés pour la mesure infrarouge ont une erreur relative moyenne de 1,66 % pour la pCO2 (mbar.m) et de 1,37 % pour la pCH4 (mbar.m). L’instrumentation IR d’un forage sur le site du Mt Terri et de deux forages sur le site de Bure (faciès C2b1 et C2d) a permis d’obtenir les courbes de transfert des deux gaz. Les courbes de transfert du CH4 ont été modélisées par un modèle de diffusion-advection qui ont permis l’évaluation de la concentration locale en CH4 dissous dans l’eau porale : elles sont comprises entre 3,06 et 14,23 mg.L-1 pour les AOP, et entre 0,36 et 1,28 mg.L-1 pour le faciès C2d et entre 0,56 et 1,55 mg.L-1 pour le faciès C2b1 des argilites de Bure. On montre que les équilibres eau/gaz/roche gouvernent la pCO2 après forage alors que la diffusion/advection explique son évolution sur le long terme. Une origine intraformationnelle des alcanes dissous est envisagée / An infrared sensor (IRTF) and an innovative Raman optical bench were implemented and developed in underground laboratories to improve our knowledge about migration mechanisms of dissolved gases (CO2 and CH4). This study is focussed on the characterisation of the initial state of the porewater of Callovo-Oxfordian marl (Bure) and Opalinus Clay (Mt Terri Middle Jurassic). These sensors are integrated into experimental devices of gas-equilibration test developed by Andra (PAC) to follow the gaseous phase behaviour in contact with the rock formation through a borehole drilled and maintained in anaerobic conditions, and initially filled with pure argon. These in situ sensors allow, on line quantitative analysis of gases released by the rock formation at low bulk pressure (<1.3 bar). Quantitative models were developed to transform peak intensities in partial pressures of gas. They give mean absolute relative errors about 1.66 % for pCO2 (mbar.m) and 1.37 % for pCH4 (mbar.m). Three years of IR monitoring of one borehole on the site of Mt Terri and two boreholes on the site of Bure (facies C2b1 and C2d) have been led. CH4 transfer curves were modelled by diffusion-advection. CH4 concentration in porewater from non-perturbed rock formation is estimated from all the experiments: concentrations between 3.06 and 14.23 mg.L-1 was obtained for Opalinus Clay, between 0.36 and 1.28 mg.L-1 for C2d facies and between 0.56 and 1.55 mg.L-1 for C2b1 facies in Callovo-Oxfordian marls of Bure. Gas/rock/water balance governs pCO2 after drilling, whereas diffusion/advection laws explain CO2 long-term profiles. An intra-formational origin of the organic gases can be proposed

La propagation d'un front de réaction-diffusion est étudiée expérimentalement dans un écoulement cellulaire multiéchelle. Le front est produit par réaction autocatalytique en solution. L'écoulement est réalisé en géométrie de Hele-Shaw par électroconvection, son caractère multiéchelle étant réalisé par l'action combinée de deux nappes d'aimants d'échelles différentes. La géométrie du front et sa vitesse moyenne de propagation sont déterminées pour une large gamme d'intensité des vortex de chaque échelle. Elles sont confortées par une simulation numérique de l'avancée du domaine brulé dans le domaine frais. L'effet de la nature multiéchelle de l'écoulement sur la vitesse moyenne du front est compris par une méthode de renormalisation dont la validation est fournie par l'obtention d'un courbe maitresse pour l'ensemble des données. / The propagation of a reaction-diffusion front is experimentally studied in a multi-scale cellular flow. The front is produced by an autocatalytic chemical reaction in an aqueous solution. The flow is generated by electroconvection and its multi-scale nature is induced by overlaying magnets of different scales. This enables an independent tune of the flow intensity at each scale. The geometry and the mean velocity of the front have been determined over a large range of scale intensities. These features are confirmed by a numerical simulation based on a burnt and fresh domain dynamics, the burnt domain expanding across the fresh one. The effect of the multi-scale nature of the flow on the mean front velocity is recovered by a renormalisation method validated by a collapse of the data onto a single curve.