Dissertations / Theses on the topic 'Tritium transport'

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 294-305).
The Fluoride Salt-Cooled High-Temperature Reactor (FHR) is a pebble bed nuclear reactor concept fueled by tristructural isotropic (TRISO) fuel particles embedded in graphite spheres and cooled by a liquid fluoride salt known as "flibe" (7LiF-BeF2). A system of models was developed which enabled analyses of the performance of a prototypical pebble bed FHR (PB-FHR) with respect to tritium production and transport, corrosion, TRISO fuel performance, and materials stability during both normal and beyond design-basis accident (BDBA) conditions. A model of TRITium Diffusion EvolutioN and Transport (TRIDENT) was developed and benchmarked with experimental data. TRIDENT integrates the effects of the chemical redox potential, tritium mass transfer, tritium diffusion through pipe walls, and selective Cr attack by tritium fluoride. Systems for capturing tritium from the coolant were proposed and simulated with TRIDENT. A large nickel permeation window reduced the tritium release rate from 2410 to 800 Ci/EFPD. A large gas stripping system reduced tritium release rates from 2410 to 439 Ci/EFPD. A packed bed of graphite located between the reactor core and the heat exchanger reduced peak tritium release rates from 2410 to 7.5 Ci/EFPD. Increasing the Li-7 enrichment in flibe from 99.995 to 99.999 wt% reduced both the tritium production rate and the necessary sizes of tritium capture systems by a factor of 4. An existing TRISO fuel performance model called TIMCOAT was modified for use with PBFHRs. Low failure rates are predicted for modern uranium oxycarbide (UCO) TRISO fuels in a PBFHR environment. Post-irradiation examinations of surrogate TRISO particles determined that the outer pyrolytic carbon layer is susceptible to cracking if flibe were to freeze around the particles. Chemical thermodynamics calculations demonstrated that common constituents of concrete will not be stable in the event they contact liquid flibe. The chemical stability of fission products in reference to the coolant redox potential was determined in the event the TRISO UCO kernel is exposed to flibe during a BDBA. Noble gases (Kr and Xe) will escape the coolant. Cesium, strontium, and iodine are retained in the salt. All other important radionuclides are retained in the kernel or within the coolant system.
by John Dennis Stempien.
Ph. D.

When different water resource components coexist in nature, they usually have an impact on each other. Studies of how they impact each other in terms of water quantities, flow dynamics, quality and contamination are therefore necessary to ensure an appropriate water and environmental management is conducted. A study in Middleburg comprised a literature review and field investigations at and around a cemetery, as part of a Water Research Commission project on impacts on the water resource from large-scale burials. A literature review conducted has enabled familiarisation with similar studies that have been conducted around the subject. Reliable methodologies have therefore been adopted from the published literature and applied on the current research. A seasonal wetland is located downgradient of the cemetery, between the cemetery and a stream that flows past the cemetery. In order to assess possible flow pathways of near-surface and groundwater from the cemetery to the stream, monthly monitoring of surface and groundwater quality and level fluctuations was carried out on the stream, as well as existing and newly installed boreholes at the cemetery. Water samples collected were analysed for inorganic constituents, tritium, and stable water isotopes. The tritium and stable water isotope results – revealed the comparative influence of rainfall and shallow groundwater contributions to streamflow, while groundwater provides base-flows as the stream levels recede. The depth to groundwater reduced with increasing rainfall, indicating direct recharge. The difference in concentrations of some inorganic parameters in the stream compared to the groundwater at the cemetery revealed the effect of natural attenuation in the vadose zone due to reduced conditions and the wetland acting as a filter to improve the water quality of the shallow interflow on reaching the stream. Since isotope data indicated to be a useful tool in studying water resource interactions, the methodology should form part of site investigations for cemetery development or on existing cemeteries to study the current impact and/or predict future impacts that the cemetery may have on the water resources. The methodology best applies in areas with multiple water resources, where there may be an interconnection between them. The isotope studies can also be used to estimate recharge and thus contaminant transport rate of the cemetery leachate.
Dissertation (MSc)--University of Pretoria, 2020.
Geology
MSc
Unrestricted

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, February, 2021
Cataloged from the official PDF version of thesis.
Includes bibliographical references (pages 319-333).
Advanced reactor concepts which use a lithium- or beryllium-bearing primary salt coolant will require technical solutions to mitigate the environmental release of tritium. One such design is the Fluoride-Salt-Cooled High-Temperature Reactor (FHR), which combines a molten Flibe (2LiF-BeF₂) salt coolant and tri-structural isotropic coated-particle fuel to produce power or process heat. Compared to current water-cooled reactors, managing tritium release from a FHR is further complicated by the mobility of tritium at high temperatures and limited knowledge of interactions between tritium and nuclear graphite in the molten fluoride salt environment. The total activity, chemical forms, and retention mechanisms for tritium in nuclear graphite were studied through thermal desorption analysis of sample materials from three in-core Flibe salt irradiations (denoted FS-1, FS-2, and FS-3) at the MIT Reactor (MITR).
Tritium desorption rates as a function of temperature were observed in distinct peak structures which are indicative of distinct trapping sites in graphite. The tritium content measurements led to estimations of overall retention in nuclear graphite of 19.6±1.9% from FS-1, 34±10% from FS-2, and 27.1±1.9% from FS-3 relative to the total calculated tritium generation in each experiment. Thermal desorption measurements of the MITR samples were consistent with previously proposed mechanisms for retention of gaseous hydrogen in graphite based on the chemical form of desorbed tritium, the activation energy of the desorption process, and the effect of excess H₂ on the desorption rate as a function of temperature. Therefore, a methodology based on gaseous retention mechanisms was proposed and developed to model the uptake of tritium into graphite from Flibe in a FHR.
A tritium retention model based on a bulk-diffusivity in graphite was developed as well as a model based on differential transport in graphite pores and grains. Using a system-level tritium transport model, the overall retention on graphite pebbles in a FHR was calculated to be 20.3% and 26.3% of the equilibrium generation rate for the bulk-diffusivity and pore and grain methods, respectively. In each case, modeling the transport and trapping of tritium inside graphite significantly reduced the retention rates compared to a retention process solely limited by mass transport in Flibe. According to the results of a sensitivity analysis, the level of tritium retention in core graphite has the largest uncertainty in the FHR tritium distribution because of relatively high standard deviations in literature measurements of tritium solubility and diffusivity in graphite.
Tritium management technology options were then examined in the system-level transport model based on permeation barrier coatings and tritium extraction systems. Permeation barrier coatings of a specified performance level applied to Flibe-facing surfaces were found to be more effective than exterior-surface coatings, while extraction systems with design constraints were able to significantly reduce overall tritium releases. A combination of the interior-surface barriers and extraction systems applied to various regions of the plant was shown to reduce tritium release into the FHR reactor building to levels below that of current light water reactors.
by Kieran Patrick Dolan.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

Deep well injection into non-potable saline aquifers of treated domestic wastewater has been used in Florida for decades as a safe and effective alternative to ocean outfall disposal. The objectives of this study were to determine the fate and transport of injected wastewater at two deep well injection sites in Miami Dade County, Florida, USA. Detection of ammonium in the Middle Confining units of the Floridan aquifer above the injection zone at both sites has been interpreted as evidence of upward migration of injected wastewater, posing a risk to underground sources of drinking water. Historical water quality data, including ammonia, chloride, temperature, and pH from existing monitoring wells at both sites from 1983 to 2008, major ions collected monthly from 2006 and 2008, and a synoptic sampling event for stable isotopes, tritium, and dissolved gases in 2008, were used to determine the source of ammonium in groundwater and possible migration pathways. Geochemical modeling was used to determine possible effects of injected wastewater on native water and aquifer matrix geochemistry. Injected wastewater was determined to be the source of elevated ammonium concentrations above ambient water levels, based on the results of major ion concentrations, tritium, dissolved noble gases and 15N isotopes analyses. Various possible fluid migration pathways were identified at the sites. Data for the south site suggest buoyancy-driven vertical pathways to overlying aquifers bypassing the confining units, with little mixing of injected wastewater with native water as it migrated upward. Once it is introduced into an aquifer, the injectate appeared to migrate advectively with the regional groundwater flow. Geochemical modeling indicated that CO2 -enriched injected wastewater allowed for carbonate dissolution along the vertical pathways, enhancing permeability along these flowpaths. At the north site, diffusive upward flow through the confining units or offsite vertical pathways were determined to be possible, however no evidence was detected for any on-site confining unit bypass pathway. No evidence was observed at either site of injected wastewater migration to the Upper Floridan aquifer, which is used as a municipal water supply and for aquifer storage and recovery.

During several decades of research and development in the field of Magnetically Confined Fusion (MCF) the preferred selection of materials for Plasma Facing Components (PFC) has changed repeatedly. Without doubt, endurance of the first wall will decide research availability and lifespan of the first International Thermonuclear Research Reactor (ITER). Materials erosion, redeposition and mixing in the reactor are the critical processes responsible for modification of materials properties under plasma impact. This thesis presents several diagnostic techniques and their applications for studies of materials transport in fusion devices. The measurements were made at the EXTRAP T2R Reversed Field Pinch operated in Alfvén laboratory at KTH (Sweden), the TEXTOR tokamak, recently shut down at Forschungszentrum Jülich (Germany) and in the JET tokamak at CCFE (UK). The main outcomes of the work are: Development and application of a method for non-destructive capture and characterization of fast dust particles moving in the edge plasma of fusion devices, as well as particles generated upon laser-assisted cleaning of plasma exposed surfaces.  Advancement of conventional broad beam and micro ion beam techniques to include measurement of tritium in the surfaces exposed in future D-T experiments.  Adaption of the micro ion beam method for precision mapping of non uniform elements concentrations on irregular surfaces.  Implementation of an isotopic marker to study the large scale materials migration in a tokamak and development of a method for fast non destructive sampling of the marker on surfaces of PFCs.

QC 20140508

In the following work, the MAVRIC sequence of the Scale6.1 code package was tested for its efficacy in calculating a wide range of shielding parameters with respect to HTGRs. One of the NGNP designs that has gained large support internationally is the VHTR. The development of the Scale6.1 code package at ORNL has been primarily directed towards supporting the current United States' reactor fleet of LWR technology. Since plans have been made to build a prototype VHTR, it is important to verify that the MAVRIC sequence can adequately meet the simulation needs of a different reactor technology. This was accomplished by creating a detailed model of the VHTR power plant; identifying important, relevant radiation indicators; and implementing methods using MAVRIC to simulate those indicators in the VHTR model. The graphite moderator used in the design shapes a different flux spectrum than water-moderated reactors. The different flux spectrum could lead to new considerations when quantifying shielding characteristics and possibly a different gamma-ray spectrum escaping the core and surrounding components. One key portion of this study was obtaining personnel dose rates in accessible areas within the power plant from both neutron and gamma sources. Additionally, building from professional and regulatory standards a surveillance capsule monitoring program was designed to mimic those used in the nuclear industry. The high temperatures were designed to supply heat for industrial purposes and not just for power production. Since tritium, a heavier radioactive isotope of hydrogen, is produced in the reactor it is important to know the distribution of tritium production and the subsequent diffusion from the core to secondary systems to prevent contamination outside of the nuclear island. Accurately modeling indicators using MAVRIC is the main goal. However, it is almost equally as important for simulations to be carried out in a timely manner. MAVRIC uses the discrete ordinates method to solve the fixed-source transport equation for both neutron and gamma rays on a crude geometric representation of the detailed model. This deterministic forward solution is used to solve an adjoint equation with the adjoint source specified by the user. The adjoint solution is then used to create an importance map that can weight particles in a stochastic Monte Carlo simulation. The goal of using this hybrid methodology is to provide complete accuracy with high precision while decreasing overall simulation times by orders of magnitude. The MAVRIC sequence provides a platform to quickly alter inputs so that vastly different shielding studies can be simulated using one model with minimal effort by the user. Each separate shielding study required unique strategies while looking at different regions in the VHTR plant. MAVRIC proved to be effective for each case.

Nous avons effectué une étude comparative du transport de la [3H] DA et de la liaison spécifique de [3H] GBR 12783 au transporteur, en utilisant des préparations obtenues à partir de striatum de rat. La dépendance des constantes cinétiques du processus de capture vis-à-vis de la concentration des ions Cl est compatible avec un cotransport DA-Cl. La dépendance de la liaison des substrats au site marque par le [3H] GBR 127833 vis-à-vis du Cl est d'autant plus importante que le substrat a une affinité marquée pour le transporteur. Comme pour la liaison de [3H] GBR 12783 aucun cation n'est capable de substituer des ions Na+ sans provoquer par lui-même une inhibition de la capture de [3H] DA. Les profils comparés de Na+ dépendance de la capture neuronale de [3H] DA et de la liaison spécifique de [3H] GBR 12783révèlent l'effet inhibiteur de certains cations (K+, Ca++, Mg++) sur les deux processus et indiquent que ce pouvoir est d'autant plus important que la concentration de Na+ est faible. La liaison des substrats nécessiterait qu'une faible concentration de Na+ (3 ) 5 mM). La liaison spécifique de [3H] GBR 12783 et la capture spécifique de [3H] DA présentent la même sensibilité vis-à-vis des ions métalliques tels que (Hg++, Cd++, Cu++), suggérant l'implication des groupements -SH dans ces deux processus. Les groupements -SH qui lient le Zn++ joueraient un rôle important dans la translocation de la DA

La diffusion des ions et des radionucléides au sein des matériaux cimentaires est l'un des facteurs les plus importants qui déterminent la durabilité et les propriétés de confinement de ces matériaux. Cette étude s'inscrit, en particulier, dans le domaine de confinement des déchets radioactifs de faible et moyenne activité. Elle consiste à mettre en évidence l'influence de la microstructure des mortiers, notamment la présence des granulats, sur la diffusion de l'eau tritiée au sein de ces matériaux. La démarche consiste, dans un premier temps, à sélectionner des formulations de mortiers à base de CEM I afin d'étudier l'influence de la teneur en granulats, de la granulométrie et du rapport eau/ciment sur les paramètres de diffusion. Des différentes techniques expérimentales complémentaires ont été utilisées afin de caractériser la structure poreuse : porosimétrie à l'eau, porosimétrie mercure, perte au feu et imagerie MEB associée à l'analyse d'image. Dans ce contexte, un protocole d'analyse d'images a été mis en place afin de quantifier la porosité à l'interface granulat/pâte. Le lien entre les propriétés de la microstructure et les paramètres de transport a été ensuite examiné. Pour cela, des essais de diffusion à l'eau tritiée (HTO) ont été conduits et des corrélations entre les paramètres de la microstructure et le transport ont été réalisées. Enfin, afin de mettre en avant le rôle des phases mésoscopiques (Matrice/granulats/ITZ) dans le mécanisme de diffusion un modèle 3D a été développé et des calculs de diffusivités équivalentes ont été effectués. La présente étude confirme la présence d'une interface granulat/pâte au voisinage des grains de sable siliceux. Cette auréole de transition (ITZ) se caractérise par une épaisseur qui varie entre 10 et 20 µm et une porosité environ trois fois plus grande que celle de la matrice cimentaire. En dessous de 55% de sable normalisé, l'effet de cette interface sur les propriétés macroscopiques de transport est faible. En effet, l'effet de dilution et de tortuosité liés aux granulats reste dominant. Par conséquent, les données acquises à l'échelle de pâte de ciment restent valables et sont extrapolable à l'échelle des mortiers. Ces résultats ont été confirmés par les calculs analytiques et numériques de la diffusivité homogénéisée. Au-delà de 55% de sable normalisé, d'autres effets liés au grands nombre de grains de sable rentrent en jeu comme les bulles d'air et les taches poreuses dus principalement à la difficulté d'obtenir des matériaux bien compactés. Ceci rend ces formulations extrêmes et ne permettent pas d'approfondir notre compréhension du lien entre la microstructure et les propriétés de transport au-delà de cette teneur en sable

Des mesures de perméabilité osmotique (Pos) ont été réalisées sur des protoplastes et des vacuoles isolés au moyen d'une technique mise au point au laboratoire. Les perméabilités sont obtenues à partir de l'observation en microscopie photonique de la cinétique des changements de volume des protoplastes ou vacuoles, consécutives à un changement rapide d'osmoticum. Nous avons mesuré Pos sur des protoplastes de racines de cultivars de blé, de colza ou de maïs à des stades de développement différents de la racine. Les valeurs mesurées ont permis de montrer que la perméabilité osmotique des protoplastes pouvait augmenter fortement en l'espace de 24 à 48 heures, ce qui suggérait la mise en place d'aquaporines au sein du plasmalemme. De même, des mesures réalisées sur des vacuoles ont montré que le tonoplaste était toujours très perméable. Une étude en présence de mercure a permis de montrer que Pos était diminuée par cet inhibiteur, indiquant la présence d'aquaporines vacuolaires. Nous avons étudié l'influence du stress hydrique sur la perméabilite osmotique de protoplastes de racine de cultivars de blé, de colza et de lin. En situation de stress, les valeurs de Pos sont augmentées pour les variétés sensibles alors qu'elles sont diminuées pour les variétés résistantes. De fortes valeurs de Pos ne semblent pas nécessaires pour permettre la croissance de la plante en situation de stress hydrique. Enfin, nous avons réalisé des mesures sur des protoplastes d'hypocotyle de mutants nains d'arabidopsis thaliana affectés dans la chaîne de biosynthèse du brassinolide. Les mesures de Pos en présence de ce régulateur de croissance ont permis de montrer que la croissance de la plantule pouvait être régulée par les flux d'eau trans-cellulaire de l'hypocotyle. L'ensemble de ces résultats souligne l'importance de la voie trans-cellulaire dans la régulation des flux d'eau dans la plante.

L'absorption et le devenir du triticonazole dans la plante de ble ont ete etudies de l'imbibition au stade gonflement, a partir de semences traitees avec du triticonazole-14c. Durant la phase d'imbibition de la semence, des quantites importantes de triticonazole penetrent dans le caryopse. Le produit se repartir dans les teguments et l'embryon et semble par la sutie etre peu transporte dans les parties aeriennes. De la levee au stade gonflement, le triticonazole est essentiellement absorbe par les racines et transporte dans les parties aeriennes par les vaisseaux du xyleme. Le produit se repartit dans les feuilles selon un gradient de concentration decroissant des etages foliaires inferieurs vers les etages foliaires superieurs. La concentration en triticonazole dans les parties aeriennes de la plante diminue fortement du stade 2-3 feuilles au stade gonflement. Cette dilution est due a la croissance vegetale et a la metabolisation de la matiere active dans les feuilles. De plus, le chargement de matiere active dans les parties aeriennes pourrait etre limite par la position du systeme racinaire par rapport a la zone de repartition du triticonazole dans le sol. La diminution de la concentration en matiere active dans les feuilles est probablement la cause de la baisse d'efficacite du triticonazole contre differentes maladies foliaires. Les possibilites de prolonger l'efficacite du triticonazole contre les maladies foliaires par une augmentation de la dose de traitement, par l'utilisation de l'enantiomere actif seul ou par un travail sur la formulation ont ete etudiees

The design of a Tokamak device is carried out initially with a 0D approach aiming at defining the plasma engineering parameters estimated with the help of empirical scaling laws, and the technological limits of the device components. The assessment of local parameters (1D) is then required to define the optimal plasma performance during the entire time evolution of the discharge. In this contest, the transport of energy and particles in fusion plasmas is one of the main actor in determining the evolution of a plasma scenario both in present experiments and in future reactors. The Joint European Torus (JET) experiment has operated in deuterium (D) and tritium (T) main ion plasma composition in 1997 (DTE1) and in 2021 (DTE2). The most important differences between the two experimental campaigns are related to the plasma facing components, carbon (C) in DTE1 and Be/W in DTE2, the increased additional heating power, and the presence of improved diagnostics, especially at the plasma edge which is determinant in the global plasma performance. After DTE1 the high levels of T retention in the C-wall have been considered unacceptable for a reactor, leading to the substitution of the C-wall with a metallic wall in the design of the International Tokamak Experimental Reactor (ITER). DTE2 campaign at JET aimed at studying D-T plasmas in the closest conditions to ITER operations. Differently from DTE1, the recent campaign focused on the stationarity of the performance and on addressing ITER-relevant aspects such as α-particles physics, plasma wall interactions and plasma heating schemes. In preparation to D-T operations, a wide experimental and modelling activity has been performed at JET in order to optimise the plasma scenarios. The focus of this thesis is the extrapolation in D-T main ion plasma composition of the JET baseline scenario. The latter is a high confinement mode (H-mode) plasma, characterized by the presence of Edge Localized Modes (ELMs), where the confinement relies on high plasma current. In ITER D-T operations, the baseline scenario is envisaged to achieve a gain factor, defined as the ratio between the fusion power and the input power, Q = Pfus/Pin ≈ 10. The objective of the thesis has been achieved through extensive integrated modelling, based on the reduced first principles transport models QuaLiKiz and TGLF employing different assumptions, and in a wide range of plasma operating conditions. QuaLiKiz and TGLF transport models have been validated in reference D plasmas, and their extrapolation capability with different plasma parameters has been tested by performing blind predictions. The results of the predictive modelling have been compared with the experimental data and analysed in order to address the sensitivity of the plasma scenario to the experimental boundary conditions. The QuaLiKiz transport model has also been validated against the experimental results produced at JET in DTE1. Before the start of the DTE2 campaign, an estimate of the particle sources required to sustain a 50-50 D-T baseline plasma has been obtained. This result has provided inputs to the JET control team in the preparation phase of the baseline fuelling scheme. This contribution boosted JET D-T operations without spending experimental time, neutron and T budget. The results of the predictive modelling performed in preparation to DTE2 are presented and discussed. The sensitivity of the predictions to plasma parameters v vi such as current, toroidal magnetic field, pedestal confinement and impurity content are analysed together with the sensitivity to the available amount of auxiliary heating power. The experimental results obtained in DTE2 by the baseline scenario are also presented and discussed. In the last part of this thesis, the implications of the modelling assumptions performed on D pulses will be compared with the assumptions done on D-T discharges with the experimental boundary conditions. The key parameters needed for reliable predictions of future experiments are discussed both in D and D-T main ion plasma composition. The estimate of particle sources obtained before the DTE2 campaign are adjusted to reproduce the experimental conditions, leading to an estimate of the different fuelling channels and an evaluation of the wall sources. The thesis is organised as follows: • In Chapter 1 we introduce fusion as a potential energy source. • In Chapter 2 we describe the Tokamak configuration and the JET experi- mental device, and we present a first comparison between the different D-T experimental campaign, and between the different scenarios prepared for DTE2. • In Chapter 3 we introduce the issue of energy and particle transport in Tokamaks, we present the theoretical background and the state of the art of transport analysis. The models used in this work are presented together with the different assumptions implemented in JINTRAC. • In Chapter 4 we present and discuss the validation of the reduced first principle transport models performed on D pulses. The extrapolations in D-T plasma mixture are presented with their sensitivity to the operating conditions. • In Chapter 5 we present and discuss the baseline results obtained in DTE2. The predictive simulations are improved by adopting the actual boundary conditions of the D-T experiments, and we discuss the impact of the different assumptions on the modelling of D plasmas extrapolated to D-T plasma mixture. We show the limits of predictive simulations in integrated modelling, and we use the predictive simulations to obtain an estimate of the different fuelling sources in the D-T experiments.

To assess the long-term performance of soil-cement materials used in source-control remediation methods (i.e. cement-based solidification/stabilization), procedures to measure or estimate contaminant migration parameters are essential. Previous research indicates that diffusion may be an important mechanism in contaminant transport through soil-cement materials. However, there is a paucity of information regarding the diffusion of contaminants through these materials. The development of a single-reservoir diffusion apparatus and methodology to assess the effective diffusion coefficient (De) and effective porosity (ne) of dissolved, conservative, inorganic chemicals for saturated, cured, monolithic soil-cement specimens is discussed. This is the only study known to investigate these parameters for these materials. The results of tritiated water diffusion tests on 14 different soil-cement mixtures are presented and the influence of curing time and mixture properties such as water-to-cement ratio, cement content, and grain-size distribution are examined. Results suggest that, to determine reasonable assessments of the longer-term parameters, soil-cement samples should be cured for a minimum of 70 days before commencing diffusion testing. Values of ne (0.21 to 0.41) and De (2.50×10-10 m2/s to 7.0×10-10 m2/s) determined are similar to those previously determined for a number other low-hydraulic conductivity materials (i.e. saturated inactive clays). The water content of the initial mixture is shown to have a substantial effect on the diffusive properties as the results indicate that both the total porosity (n) and the effective porosity, ne, generally increase with increasing initial water content. For the range of soils used in this investigation, grain-size distribution did not have a substantial effect on the values of ne or De determined from diffusion testing. The adaptation of a double-reservoir diffusion testing apparatus and methodology to evaluate the distribution coefficient (Kd) and De of organic contaminants is also presented. This apparatus is used to evaluate Kd and De of benzene, ethylbenzene, naphthalene, and trichloroethylene for three soil-cement mixtures. Values of Kd (0 to 2.5 cm3/g depending on the compound and soil-cement mixture tested) determined from diffusion testing, batch testing, and theoretical estimates from the literature were in general agreement. Values of De for the organic compounds ranged from 1.50×10-10 to 3.0×10-10 m2/s.

Current bioethanol production is predominantly based on starch from cereal crops such as corn and wheat which leads to increased competition for such crops between the food, feed and bioethanol industries. Thus, enhancing the sustainability of the bioethanol industry, at least in the short term, requires increased starch yield per seed or per unit area. Starch content of wheat grains is partly determined by sucrose transport efficiency from the source (the leaf) to the sink organ (the grain) which is partly mediated by sucrose transporter (SUT) proteins. Only one functional SUT (TaSUT1) gene of wheat is known to date. Using molecular gene cloning approaches, this thesis project identified the three homeologues of a new SUT (TaSUT2) gene from hexaploid wheat and demonstrated their functionality as sucrose transporters through heterologous expression in mutant yeast. Characterization of the spatio-temporal expression of TaSUT2 suggested its role in phloem loading, unloading and sucrose retrieval.

The Russian wheat aphid (Diuraphis noxia) feeds preferentially from the phloem of longitudinal veins of nonresistant wheat leaves. The xenobiotic, 5,6-CFDA was applied to exposed leaf blade mesophyll cells in control and aphid-infested plants. In control plants, the fluorophore moved approximately 5–6cm from the point of application of 5,6-CFDA within 3h of application. The fluorochrome was transported in the sieve tube companion cell complex, including those in the numerous interconnecting transverse veins. Leaf blades on which the Russian wheat aphid had been feeding demonstrated a marked decrease in 5,6-CF transport. Aphids feeding on the leaves formed local sinks and redirected the fluorophore (and presumably associated assimilate) to the aphids’ gut, with little longitudinal translocation of 5,6-CF below inserted stylets or aphid feeding areas. Aniline blue staining revealed massive deposits of wound and reaction callose caused by the aphids, with callose associated with the sieve plates, pore-plasmodesma between the companion cells and their associated sieve tubes, as well as with plasmodesmal aggregates in parenchymatous elements within the vascular bundles. Leaves that had been colonised by aphids but from which the aphids were removed, showed extensive wound callose deposits, which persisted for up to 48h after removal of aphid colonies, suggesting that the damage caused by aphid feeding is a long-term, non-transient event in non-resistant plants.

The Russian wheat aphid (Diuraphis noxia) feeds preferentially from the phloem of longitudinal veins of nonresistant wheat leaves. The xenobiotic, 5,6-CFDA was applied to exposed leaf blade mesophyll cells in control and aphid-infested plants. In control plants, the fluorophore moved approximately 5–6cm from the point of application of 5,6-CFDA within 3h of application. The fluorochrome was transported in the sieve tube companion cell complex, including those in the numerous interconnecting transverse veins. Leaf blades on which the Russian wheat aphid had been feeding demonstrated a marked decrease in 5,6-CF transport. Aphids feeding on the leaves formed local sinks and redirected the fluorophore (and presumably associated assimilate) to the aphids’ gut, with little longitudinal translocation of 5,6-CF below inserted stylets or aphid feeding areas. Aniline blue staining revealed massive deposits of wound and reaction callose caused by the aphids, with callose associated with the sieve plates, pore-plasmodesma between the companion cells and their associated sieve tubes, as well as with plasmodesmal aggregates in parenchymatous elements within the vascular bundles. Leaves that had been colonised by aphids but from which the aphids were removed, showed extensive wound callose deposits, which persisted for up to 48h after removal of aphid colonies, suggesting that the damage caused by aphid feeding is a long-term, non-transient event in non-resistant plants.

The world population is rising, placing increasing demands on food production. One way to contribute to food security is by improving yields of staple crops like wheat. Yield can be calculated from the product of plant biomass and harvest index (the ratio of grain yield to above ground biomass). Since harvest index of wheat has already reached its maximum biological limit in some environments, attention is now focused on increasing crop biomass. Efficient interception of photosynthetically active radiation and effective photosynthetic sugar production underpin yield, however, little breeding has been done for photosynthetic performance. Exploiting existing genetic variation for important photosynthetic traits such as photosynthetic capacity (Pc) and photosynthetic efficiency (Peff) will help to improve wheat yield. CO2 assimilation rate, which is a commonly measured parameter for assessing photosynthetic performance, is found to vary across wheat genotypes. Two additionally important parameters are Rubisco activity (Vcmax) and electron transport rate (J). There is much less information reported regarding genetic variation of these two latter parameters because measurements of CO2 response curves with gas exchange used to derive Vcmax and J are slow and unsuitable for rapid screening of many genotypes in the field. The two main objectives of this project were firstly, to find out if there is genetic variation for these important photosynthetic traits in wheat, and secondly, to develop a rapid method for screening photosynthetic and leaf attributes in different wheat genotypes. To deal with variable leaf temperatures in the field and accurately estimate Vcmax and J, improved values for the temperature dependence of several Rubisco kinetic parameters were needed. These temperature-dependencies were derived from measurements made under controlled conditions. A method for rapidly estimating variation in Pc components Vcmax and J and in other photosynthetic traits was developed based on calibration of leaf reflectance spectra against photosynthetic parameters derived using conventional gas exchange, morphological (leaf mass per unit area, LMA) and chemical (nitrogen and chlorophyll per unit area) measurements of 76 wheat genotypes screened in several different environments. When observed data were compared against predictions from reflectance spectra, correlation coefficients (R2 values) of 0.62 for Vcmax25, 0.71 (J), 0.89 (LMA) and 0.93 (Narea), were obtained. Reflectance spectra from an additional 458 elite and landrace wheat genotypes were measured to further assess variation in photosynthetic traits. There were significant differences between wheat genotypes in Vcmax25 per unit N, which is a good measure of Peff. Environment presented interaction with genotypes for Pc and Peff when measurements performed in glasshouse & field or in Australia & Mexico were compared. In future, linking genotypic variation for photosynthetic traits to DNA-based genetic markers will permit even faster selection of genotypes in breeding. Reflectance spectra should be a good tool to accelerate identification and selection of wheat genotypes and detection of important genomic regions for photosynthetic capacity and efficiency in wheat.