Mechanisms Of Ingress Research Articles

Hydro-sedimentological drivers of fine sediment ingress in a gravel-bed river

Most studies investigating fine sediment ingress in gravel-bed rivers have been conducted at the laboratory scale, and even fewer have explored the ingress processes of flocculated particles. Here, an extensive in-situ sampling programme was undertaken to investigate hydro-sedimentological drivers of interstitial fine sediment accumulation and to evaluate fine sediment ingress directional mechanisms in a gravel-bed river located on the eastern slopes of the Rocky Mountains in southern Alberta. Three sediment trap designs were installed across seven deployment cycles at four sites along the river. Instantaneous discharge, suspended solids concentration, and particle size distributions (of suspended and ingressed particles) were measured, while relevant hydraulic parameters were modelled with a flow model (MOBED). Distinct patterns of ingress dynamics between non-cohesive and cohesive fractions of fine sediment were observed. While the assessed hydro-sedimentological parameters did not statistically explain the ingress rates of non-cohesive 0.5 – 2 mm particles, the opposite was observed for < 0.5 mm particles, which were mostly transported in flocculated form. For flocculated sediment, horizontal ingress accounted for ∼ 60 % of interstitial accumulation. Directional ingress mechanisms, however, were dependent on flow conditions for both particle size fractions, with vertical and horizontal accumulations becoming more important during higher and lower energy flows, respectively. Our observations demonstrate the importance of ingress for the interstitial accumulation of fine sediment, even during events with flow above the critical threshold conditions for fine sediment gravitational deposition. Despite the comparable ingress rates to other studies, no interstitial clogging was observed in this study, demonstrating the channel potential storage capacity, which has implications for legacy impacts from landscape disturbances in the Crowsnest River catchment.

Challenges in measuring fine sediment ingress in gravel‐bed rivers using retrievable sediment trap samplers

Abstract“Excess” interstitial fine sediment (&lt;2 mm) is known to cause deleterious impacts on streambed ecosystems. Current methodologies available to assess ingress and its vertical and horizontal components still lack standardization, and the accuracy of commonly used assessments is still debatable. Here, we evaluate three fine sediment trap designs that measure only vertical (V), only horizontal (H), and both vertical and horizontal (HV) ingress mechanisms. Sediment traps were deployed in triplicates to: (i) evaluate measurement variability within traps of the same type; (ii) evaluate the effects of trap design on particle size distributions of infiltrated fine sediment and; (iii) assess methodologies used to calculate vertical and horizontal ingress mechanisms. Ingress rates were recorded for each sediment trap during seven deployment periods (lasting from 2 to 10 days) at a range of flow conditions at four sites. A total of 252 traps were deployed. Results from the triplicate assessment of traps with the same design showed that most measurements presented high variability and that particle size distributions were significantly affected by trap design. Here, different sediment traps were able to estimate directional ingress mechanisms. However, direct comparison between HV with either H or V traps led to an overestimation of horizontal or vertical ingress mechanisms, respectively. Better estimations were found when comparing HV observations to half the accumulation in either H or V, due to the proportional trap volume available for each accumulation mechanism according to trap design.

The impact of mainstream ingress on the leakage flow and loss in partial shrouded turbines

The vital source of the leakage loss in shrouded LP turbines is the interaction between the leakage flow and mainstream at the exit cavity and downstream of the rotor tip. This paper numerically investigates the effect of the shroud design on the leakage loss. The results show that the mainstream ingress in the exit cavity is the key flow feature affecting the intensity and the resultant loss of the interaction between the two flows, which is highly intenser in partial shrouded turbines than full shrouded turbines and causes three aspects of impact: Firstly, the abundant amount of ingested mainstream raises the pressure in the exit cavity, reducing the axial leakage flow rate through the sealing structure. However, there is circumferential leakage flow at the rotor trailing edge due to the lack of the blockage of the shroud platform. In addition, the ingested mainstream also develops into backflow and a streamwise vortex in the exit cavity, intensifying the mixing of the leakage flow and mainstream. Thirdly, the pressure raise in the cavity promotes the convergence of the cavity outflow at the suction side of the rotor blade, thus expanding the impact region of the leakage flow and increasing the mixing loss downstream. The above impacts result in an efficiency decrease of up to 0.90% in the partial shrouded turbine compared to the full shrouded turbine. Based on the loss mechanisms of mainstream ingress, this paper presents an optimized shroud design, which can effectively reduce the loss in the rotor tip by suppressing the mainstream ingress phenomenon. In this way, the optimized shroud design has improved considerably the aerodynamic efficiency by about 0.50%.

From superhydrophilicity to superhydrophobicity: high-resolution neutron imaging and modeling of water imbibition through porous surfaces treated with engineered nano-coatings

This paper reports on a superhydrophilic to superhydrophobic transformation of TiO2 nanoparticles doped zinc phosphate coating systems when a hydrophobic agent is applied. The objective of the reported research was to demonstrate the feasibility of a neutron imaging technique for evaluating the performance of the proposed nano-coating system and reveal the differences in water ingress mechanisms which are specific to plain, superhydrophilic, overhydrophobic, and superhydrophobic specimens. The engineered nano-coatings were designed to improve hydrophobic response with inducing the required roughness pattern and introducing the photocatalytic performance. The effectiveness of the coatings was assessed using high-resolution neutron imaging (HR-NI), SEM, CLSM, and XRD techniques. High-resolution neutron imaging revealed that the superhydrophobic coating effectively prevents water ingress into the porous ceramic substrate, whereas water imbibition was observed for superhydrophilic coating during the test duration. The moisture transport kinetics was modeled based on the Richards equation for plain ceramic and superhydrophilic specimens using obtained penetration depth values from HR-NI. SEM, CLSM, and XRD studies confirm the desired TiO2-doped zinc phosphate coatings with increased surface roughness, photocatalytic reactivity, and chemical bonding. The research results demonstrated that a two-layer superhydrophobic system is capable of creating effective water barriers on the surface with contact angles of 153°, which remained effective even after surface damage.

Bridging the Gap: Assessing Material Performance of Laboratory Specimens and Concrete Structures.

Chloride ingress and carbonation pose a significant risk of steel rebar corrosion in concrete structures. Various models exist to simulate the initiation phase of rebar corrosion, addressing both carbonation and chloride ingress mechanisms separately. These models also consider the environmental loads and material resistances, typically determined through laboratory testing based on specific standards. However, recent findings show significant differences between material resistances obtained from standardized laboratory specimens and those extracted from real structures, with the latter exhibiting inferior performance on average. To address this issue, a comparative study was conducted between laboratory specimens and on-site test walls or slabs, all cast using the same concrete batch. This study encompassed five construction sites featuring different concrete compositions. While laboratory specimens adhered to European curing standards, the walls were subjected to formwork curing for a predetermined period (typically 7 days) to simulate practical conditions. In some instances, a portion of the test walls/slabs received only one day of surface curing to emulate inadequate curing conditions. Subsequent testing of compressive strength and resistance to chloride ingress revealed that field specimens exhibited lower material resistance compared to their laboratory counterparts. This trend was also observed in the modulus of elasticity and carbonation rate. Notably, shorter curing periods further compromised performance, particularly resistance to chloride ingress and carbonation. These findings highlight the importance of establishing acceptance criteria not only for concrete delivered to construction sites but also for ensuring the quality of the actual structure.

The antimicrobial resistance profiles of Escherichia coli and Pseudomonas aeruginosa isolated from private groundwater wells in the Republic of Ireland

The role of the natural environment in the dissemination of antimicrobial resistant bacteria has been increasingly recognised in the literature. However, knowledge surrounding the critical factors and mechanisms mediating their occurrence is still limited, particularly in relatively ‘pristine’ groundwater environments. In the Republic of Ireland (RoI), a country characterised by high groundwater reliance, household-based (unregulated) wells provide drinking water to 11% of the population. These private wells are generally located in rural areas, where the risk of microbiological contamination is high due to intensive agricultural practices and high reliance on domestic wastewater treatment systems; both of which are also potential sources of antimicrobials and antimicrobial resistant bacteria. Accordingly, the current research sought to elucidate current rates of antimicrobial resistant bacteria and the principal factors associated with their presence in private wells in the RoI. A total of 250 samples (from 132 wells nationwide) were assessed for the presence of faecal (Escherichia coli) and environmental (Pseudomonas aeruginosa) bacteria, with single isolates from each contaminated sample tested phenotypically against 18 and 9 antimicrobials, respectively. Findings show that while 16.7% of E. coli (n = 8/48) were categorically resistant to ≥1 antimicrobial, with a further 79.2% classified as intermediately resistant, no categorical resistance was found among P. aeruginosa isolates (n = 0/6), with just one intermediately resistant isolate detected. Multivariate regression modelling indicates significantly higher odds of resistant E. coli detection in concurrence with elevated cattle density (OR = 1.028, p = 0.032), aligning with findings of highest resistance rates to veterinary antimicrobials (e.g., streptomycin = 14.6%, tetracycline = 12.5%, and ampicillin = 12.5%). Multivariate model results also suggest overland flow culminating in direct wellhead ingress as a primary ingress mechanism for resistant E. coli. Study findings may inform groundwater source protection initiatives and antimicrobial resistance surveillance moving forward.

Investigation of the Hydrogen Ingress and Embrittlement Induced By Corrosion of API 5L Natural Gas Pipeline Steels

Internal corrosion of natural gas pipelines is a major cause of many related accidents. In addition to the metal loss due to corrosion, hydrogen ions produced during corrosion can lead to the degradation of ductility of metals used in these pipelines. The effect of hydrogen generated through internal corrosion on current pipeline steels was studied. Three grades of API 5L steels commonly used in natural gas infrastructure were investigated: X56, X65, and X100. The rates of hydrogen diffusion were determined electrolytically via a Devanathan-Stachurski cell. The steels were subjected to hydrogen embrittlement tests using electrolytic hydrogen charging and constant strain rate tensile tests. The microstructure analysis of the investigated materials and the fracture surfaces was performed via scanning electron microscopy (SEM). This presentation reports on work to extend the life of the natural gas pipeline network via understanding the mechanisms of hydrogen ingress and subsequent embrittlement induced by corrosion processes.

Spatiotemporal dynamics of Escherichia coli presence and magnitude across a national groundwater monitoring network, Republic of Ireland, 2011–2020

Groundwater is a vital drinking water resource and its protection from microbiological contamination is paramount to safeguard public health. The Republic of Ireland (RoI) is characterised by the highest incidence of verocytotoxigenic Escherichia coli (VTEC) enteritis in the European Union (EU), linked to high reliance on unregulated groundwater sources (~16% of the population). Yet, the spatio-temporal factors influencing the frequency and magnitude of microbial contamination remain largely unknown, with past studies typically constrained to spatio-temporally ‘limited’ sampling campaigns. Accordingly, the current investigation sought to analyse an extensive spatially distributed time-series (2011−2020) of groundwater monitoring data in the RoI. The dataset, compiled by the Environmental Protection Agency (EPA), showed ‘high’ contamination rates, with 66.7% (88/132) of supplies testing positive for E. coli, and 29.5% (39/132) exceeding concentrations of 10MPN/100 ml (i.e. gross contamination) at least once during the 10-year monitoring period. Seasonal decomposition analyses indicate that E. coli detection rates peak during late autumn/early winter, coinciding with increases in annual rainfall, while gross contamination peaks in spring (May) and late-summer (August), likely reflecting seasonal shifts in agricultural practices. Mixed effects logistic regression modelling indicates that monitoring sources located in karst limestone are statistically associated with E. coli presence (OR = 2.76, p = 0.03) and gross contamination (OR = 2.54, p = 0.037) when compared to poorly productive aquifers (i.e., transmissivity below 10m2/d). Moreover, 5-day and 30-day antecedent rainfall increased the likelihood of E. coli contamination (OR = 1.027, p < 0.001 and OR = 1.005, p = 0.016, respectively), with the former also being associated with gross contamination (OR = 1.042, p < 0.001). As such, it is inferred that preferential flow and direct ingress of surface runoff are the most likely ingress mechanisms associated with E. coli groundwater supply contamination. The results presented are expected to inform policy change around groundwater source protection and provide insight for the development of groundwater monitoring programmes in geologically heterogeneous regions.

Wheat endophytes and their potential role in managing abiotic stress under changing climate.

Wheat (Triticum aestivum L.) cultivation differs considerably in respect of soil type, temperature, pH, organic matter, moisture regime, etc. Among these, rising atmospheric temperature due to global warming is most important as it affects grain yield drastically. Studies have shown that for every 1°C rise in temperature above wheat's optimal growing temperature range of 20-25°C, there is a decrease in 2.8days and 1.5mg in the grain filling period and kernel weight, respectively, resulting in wheat yield reduction by 4-6 quintal per hectare. Growing demand for food and multidimensional issues of global warming may further push wheat crop to heat stress environments that can substantially affect heading duration, percent grain setting, maturity duration, grain growth rate and ultimately total grain yield. Considerable genetic variation exists in wheat gene pool with respect to various attributes associated with high temperature and stress tolerance; however, only about 15% of the genetic variability could be incorporated into cultivated wheat so far. Thus, alternative strategies have to be explored and implemented for sustainable, more productive and environment friendly agriculture. One of the feasible and environment friendly option is to look at micro-organisms that reside inside the plant without adversely affecting its growth, known as 'endophytes', and these colonize virtually all plant organs such as roots, stems, leaves, flowers and grains. The relationship between plant and endophytes is vital to the plant health, productivity and overall survival under abiotic stress conditions. Thus, it becomes imperative to enlist the endophytes (bacterial and fungal) isolated till date from wheat cultivars, their mechanism of ingression and establishment inside plant organs, genes involved in ingression, the survival advantages they confer to the plant under abiotic stress conditions and the potential benefits of their use in sustainable wheat cultivation.

Multifactorial Chloride Ingress Model for Reinforced Concrete Structures Subjected to Unsaturated Conditions

The attack of chloride ions is one of the most important factors affecting reinforced concrete (RC) durability. Chloride ingress into concrete is usually studied by assuming constant diffusivity and constant surface chloride concentration. However, these two approximations could badly estimate the chloride concentration in RC structures and then the lifetime assessment. Several factors influence the chloride concentration and ingress mechanisms in the convection area. In this paper, a new multifactorial and multiphase model to account for some effects on chloride surface concentrations in the convection zone is proposed. 136 values have been collected to identify the position and the chloride concentration in the border between the diffusion and convection zones. In addition, a time-dependent multifactorial diffusivity is considered. Diffusivity, which is the key parameter of the mechanical diffusion accounts in this paper for the water/cement ratio, chloride binding, temperature, concrete age, internal humidity, concrete deformation, and damage. The surface chloride model considers environment humidity, temperature, superficial concrete irregularities, and convection area of concrete. Advanced numerical solutions have been carried out to consider space and time dependencies in the model. Results show that the error function-based solutions could underestimate the chloride concentration C for periods &lt; 10 years and for concrete depths &gt; 4.0 cm in comparison with the proposed model.

A comparison study of water diffusion in unidirectional and 2D woven carbon/epoxy composites

AbstractThe use of CFRP composites is significantly increasing in the aerospace, automotive, and marine industries, particularly in safety critical primary structures. This work presents a newly developed experimental approach to investigate the directional diffusion of water in CFRP composites with the use of Fick's law. The approach is used to study the effect of fiber architecture on directional diffusion rates, with a particular focus on the role of fiber waviness in the diffusion process. A comparison of water diffusion is made in three different fiber architectures: Unidirectional (UD), plain weave, and twill weave. The specimens were fully immersed in 90°C purified water until their maximum moisture saturation was achieved, with some specimens being selectively exposed from the edges only to obtain the directional diffusion coefficients. The water penetration process into the CFRP structure initiate from the micro‐cracks and defects. The experimental work of this study shows sharp mass increases within the first stage followed by an equilibrium stage where saturation is present. The interfacial region is found to be a critical parameter where detachment of the interfacial fiber/matrix bonding is observed further demonstrating the potential effect of different fiber architecture in this region. UD fiber architecture showed ~20% higher diffusion coefficient in the Dx,y direction compared with plain and twill woven architectures. The weave patterns in 2D woven fiber architectures are therefore believed to play a key role on the moisture ingress mechanism and subsequently contributed in slowing down the capillary process in the interfacial region. This has implications for materials development and selection for CFRP composites used in moist environments.

Methods of Test for Concrete Permeability: A Critical Review

Abstract The transport of liquids, gasses, and aggressive agents into concrete is responsible for a variety of durability issues. To obtain the low-permeability concrete required for long-lasting, sustainable infrastructure, stakeholders desire the ability to specify concrete based upon the permeability rating for specific uses. The mechanisms of moisture ingress into concrete are complex phenomena, and they are highly dependent on materials, mixture characteristics, curing conditions, and other factors. This review article provides an overview of the available permeability test methods and identifies existing gaps in the current field and knowledge. It discusses the mechanisms and key factors influencing moisture movement within concrete (capillary suction, absorption, water, and gas permeability) and outlines the procedures, advantages, and limitations of available permeability test methods. Despite a variety of tests available for water permeability, widespread acceptance for use of a single (or even a few) tests has not been achieved. No clear link exists between these tests and acceptable field performance. Additionally, several tests are viewed as problematic from a time, cost, or variability standpoint. Therefore, improved rapid permeability tests are needed to provide a pathway for agencies to move toward performance specifications with confidence. Recommendations regarding future work to support the development of improved test methods and, potentially, a model that would predict moisture ingress based on electrical resistivity, are also presented.

Moisture Ingress at the Molecular Scale in Hygrothermal Aging of Fiber-Epoxy Interfaces.

Almost all applications of carbon fiber reinforced composites are susceptible to water aging, either via ambient humidity or through direct exposure to liquid water environments. Although the impacts of water aging in composites can be readily quantified via experimental efforts, details regarding the mechanisms of moisture ingress and aging, particularly at the incipient stages of aging under hygrothermal conditions, have proven challenging to resolve using experimental techniques alone. A deeper understanding of the factors that drive incipient moisture ingress during aging is required for more targeted approaches to combat water aging. Here, molecular dynamics simulations of a novel epoxy/carbon fiber interface exposed to liquid water under hygrothermal conditions are used to elucidate molecular details of the moisture ingress mechanisms at the incipient stages of the aging process. Remarkably, the simulations show that the fiber-matrix interface is not vulnerable to a moisture-wicking type of incipient water ingress and does not readily flood in these early stages of water aging. Instead, water is preferentially absorbed via the matrix-water interface, an ingress pathway that is facilitated by the dynamic mobility of polymer chains at this interface. These chains present electronegative sites that can capture water molecules and provide a conduit to transiently exposed pores and channels on the polymer surface, which creates a presoaked staging reservoir for subsequent deeper ingress into the composite. Characterization of the absorbed water is according to hydrogen bonding to the matrix, and the distributions and transport behavior of these waters are consistent with experimental observations. This work introduces new insights regarding the molecular-level details of moisture ingress and spatial distribution of water in these materials during hygrothermal aging, informing future design directions for extending both the service life and shelf life of next-generation composites.

Durability based service life prediction of bacterial concrete

Concrete durability is one the essential factors effecting the service life of structures. The problem in durability of structures not only gives great impact on the functionality of the structures themselves but also on their environment. The maintenance and repair process resulting from the problems will consume a lot of energy and resources. The use of bacteria as an effort for repairing concrete cracks becomes popular recently. Crack formation is a common problem in many concrete structures. Durability problems may rise due to these cracks usually reducing concrete integrity and permeability. There are many degradation mechanisms affecting concrete performance, two of them are carbonation and chloride ingress. Several researches prove increased resistance towards those two mechanisms. This paper is aimed to simulate service life of bacterial concrete based on carbonation and chloride ingress mechanisms incorporating carbonation rate constants and chloride migration coefficients. It is concluded that the utilization of bacteria in concrete is prospective in increasing the durability of concrete structures.

Influence of walls surface topography on water droplet damping and absorption for earthen constructions

The use of raw earth as a building material is gaining interest, indeed raw earth has considerable environmental advantages. However, the correct use and development of such materials requires an accurate assessment of the water content within the walls during service life, since this latter strongly impacts both their mechanical and thermal properties. For that purpose, a good knowledge of water ingress mechanisms at the surface of earthen walls is essential, due to impacting rain for example. In this context, this paper aims at studying the impact of the compacted earth blocks surface topography on the absorption and damping of water droplet through two experimental devices. Surface topography of samples made with three different raw earths is determined using a new chromatic confocal sensor technique revealing the multi-scale roughness of this material through the waviness Wa and the roughness Ra. With the water damping experimental device can be followed the maximal height h(t) and the diameter D(t) of the impacting droplet along the time. Despite the quickness of the absorption (max 50 m s), two behaviors can be distinguished depending on the samples: oscillating or cushioned. The results show that the Dmax of the droplet increases with the Ra while the time of absorption drastically decreases until a threshold.

Numerical modeling of hot gas ingestion into the rotor-stator disk cavities of a subscale 1.5-stage axial gas turbine

Both steady and unsteady Reynolds Averaged Navier-Stokes (RANS) techniques coupled with the k-ε and k-ω(SST) turbulence models are utilized to study the flow characteristics and hot gas ingestion through rim seal in a subscale 1.5-stage axial gas turbine. A scalar transport equation is solved for a tracer gas to represent the coolant flow interaction with the main stream flow. To validate the numerical methodology, radial pressure and sealing effectiveness distributions are compared with the experimental data. The k-ω(SST) turbulence model has the capability to predict secondary flow characteristics, reattachment and separation, thus leading to better agreement with the experimental data. Both radial and circumferential pressure distributions are analyzed to get deeper insight into rotationally and externally induced ingress mechanisms. The circumferential pressure peak-to-trough amplitude is significantly attenuated in the cavity region compared to annulus region. Finally, different purge flow rates and rotational speeds are examined. Results indicate that as purge flow rate increases, the static pressure in the disk cavity region raises remarkably and consequently the sealing effectiveness improves. Averaged sealing effectiveness in the rim cavity decreases linearly with the rotational speed. To visualize different mechanisms of ingestion, streamline and flow field are shown.

An Efficient Chloride Ingress Model for Long-Term Lifetime Assessment of Reinforced Concrete Structures Under Realistic Climate and Exposure Conditions

Chloride penetration is among the main causes of corrosion initiation in reinforced concrete (RC) structures producing premature degradations. Weather and exposure conditions directly affect chloride ingress mechanisms and therefore the operational service life and safety of RC structures. Consequently, comprehensive chloride ingress models are useful tools to estimate corrosion initiation risks and minimize maintenance costs for RC structures placed under chloride-contaminated environments. This paper first presents a coupled thermo-hydro-chemical model for predicting chloride penetration into concrete that accounts for realistic weather conditions. This complete numerical model takes into account multiple factors affecting chloride ingress such as diffusion, convection, chloride binding, ionic interaction, and concrete aging. Since the complete model could be computationally expensive for long-term assessment, this study also proposes model simplifications in order to reduce the computational cost. Long-term chloride assessments of complete and reduced models are compared for three locations in France (Brest, Strasbourg and Nice) characterized by different weather and exposure conditions (tidal zone, de-icing salts and salt spray). The comparative study indicates that the reduced model is computationally efficient and accurate for long-term chloride ingress modeling in comparison to the complete one. Given that long-term assessment requires larger climate databases, this research also studies how climate models may affect chloride ingress assessment. The results indicate that the selection of climate models as well as the considered training periods introduce significant errors for mid- and long- term chloride ingress assessment.

Correlation between chloride-induced corrosion initiation and time to cover cracking in RC Structures

Numerical value of correlation between effective parameters in the strength of a structure is as important as its stochastic properties in determining the safety of the structure. In this article investigation is made about the variation of coefficient of correlation between effective parameters in corrosion initiation time of reinforcement and the time of concrete cover cracking in reinforced concrete (RC) structures. Presence of many parameters and also error in measurement of these parameters results in uncertainty in determination of corrosion initiation and the time to crack initiation. In this paper, assuming diffusion process as chloride ingress mechanism in RC structures and considering random properties of effective parameters in this model, correlation between input parameters and predicted time to corrosion is calculated using the Monte Carlo (MC) random sampling. Results show the linear correlation between corrosion initiation time and effective input parameters increases with increasing uncertainty in the input parameters. Diffusion coefficient, concrete cover, surface chloride concentration and threshold chloride concentration have the highest correlation coefficient respectively. Also the uncertainty in the concrete cover has the greatest impact on the coefficient of correlation of corrosion initiation time and the time of crack initiation due to the corrosion phenomenon

Density functional theory metadynamics of silver, caesium and palladium diffusion at β-SiC grain boundaries

The use of silicon carbide in coated nuclear fuel particles relies on this materials impermeability towards fission products under normal operating conditions. Determining the underlying factors that control the rate at which radionuclides such as Silver-110m and Caesium-137 can cross the silicon carbide barrier layers, and at which fission products such as palladium could compromise or otherwise alter the nature of this layer, are of paramount importance for the safety of this fuel. To this end, DFT-based metadynamics simulations are applied to the atomic diffusion of silver, caesium and palladium along a Σ5 grain boundary and to palladium along a carbon-rich Σ3 grain boundary in cubic silicon carbide at 1500K. For silver, the calculated diffusion coefficients lie in a similar range (7.04×10−19–3.69×10−17m2s−1) as determined experimentally. For caesium, the calculated diffusion rates are very much slower (3.91×10−23–2.15×10−21m2s−1) than found experimentally, suggesting a different mechanism to the simulation. Conversely, the calculated atomic diffusion of palladium is very much faster (7.96×10−11–7.26×10−9m2s−1) than the observed penetration rate of palladium nodules. This points to the slow dissolution and rapid regrowth of palladium nodules as a possible ingress mechanism in addition to the previously suggested migration of entire nodules along grain boundaries. The diffusion rate of palladium along the Σ3 grain boundary was calculated to be slightly slower (2.38×10−11–8.24×10−10m2s−1) than along the Σ5 grain boundary. Rather than diffusing along the precise plane of the boundary, the palladium atom moves through the bulk layer immediately adjacent to the boundary as there is greater freedom to move.

MODELLING INGRESS MECHANISMS FOR POWER STATIONS ON THE SOUTHERN EAST COASTS OF SCOTLAND

This study aims to investigate the mechanisms of jellyfish and seaweed ingress that could cause problems to the smooth operations of power plants located on coastline when their cooling water inlets are exposed to these kinds of attacks. Ingress events may lead to clogging of the filters and result in a shutdown of the power plant. Jellyfish are presenting a particular problem with an increase in populations observed globally due to warmer coastal waters, over-fishing and pollution. The ingress mechanisms and conditions are still poorly understood and difficult to predict numerically. The ingress mechanisms are being investigated through numerical modelling of hydrodynamics around the east coast of Scotland near to Dunbar. Torness power station, located in the study area, has been subjected to jellyfish ingress resulting in a controlled temporary shutdown of the two power station units, at a considerable cost to the operators. This project aims to provide an understanding of ingress mechanisms by numerical modelling of the hydrodynamics and the assessment of the conditions that govern the transport of growth of the marine life.