Simulated Pore Water Research Articles

Iron-coated nutshell waste bioadsorbents: Synthesis, phosphate remediation, and subsequent fertilizer application

The increasing incidence of freshwater nutrient pollution worldwide has highlighted the need for improved phosphate capture technologies. Successful phosphate recovery from agricultural sources and commercial wastewater can help prevent freshwater algal bloom contamination, while also reducing the dependency on finite phosphate reserves. Biodegradable biosorbents have the potential to remove phosphate from water; however, their potential as slow-release fertilizers has not been tested. Novel biosorbents were developed by coating pistachio and walnut shells with iron oxides; batch and column experiments were conducted to investigate their adsorption capacities and performances. Surface characterization studies were also conducted to investigate changes in the surface area and morphology. The potential of using iron-coated shells loaded with phosphorus as slow-release fertilizers was also evaluated. Advanced characterization techniques (scanning electron microscopy, Brunauer-Emmett-Teller (BET) physisorption analysis, and x-ray diffraction) showed that hematite was successfully coated onto the surface, resulting in increased surface area and roughness. The iron-coated pistachio and walnut shell phosphate removal capacity was 12.63 mg g−1 and 9.25 mg g−1, respectively. The phosphate sorption data fitted well with the Freundlich isotherm model and pseudo-second-order kinetics. Inner sphere complex formation, coprecipitation, diffusion, and electrostatic attraction were the main uptake mechanisms. Results from sequential release experiments with simulated pore water suggested both fast and slow desorption components. The Mehlich-3 extraction revealed that more than 90% of the released phosphate was available for plant uptake. In addition, nutrient priming showed that corn seed shoot growth increased by more than 43% when pretreated with phosphate-loaded biosorbents, demonstrating that the released phosphate could be used for plant growth. This research provides a pathway for two important zero-waste, cyclical economic goals: (1) the beneficial use of agricultural waste, and (2) a low-cost technology that can recover phosphorus from waste streams while potentially adding an additional unconventional phosphate source to apatite mineral ores.

The anoxic corrosion of mild steel in a cementitious repository environment

AbstractThe long‐term disposal of low‐ and intermediate‐level radioactive waste is anticipated to involve the encapsulation of the material within a cementitious matrix before placement in a deep geological repository. After sealing, the waste repository will become anoxic and the corrosion of emplaced metals will result in the production of hydrogen gas. Knowledge of the rate at which this hydrogen is generated is valuable in that it permits the assessment of pressure build‐up within the repository. The corrosion behavior of mild steel has been monitored through the generation of hydrogen gas, under simulated repository conditions that mimic various stages of cement evolution. It was found that, when cement is used to encapsulate steel, the passage of several years is required for the steel and cement to reach a steady hydrogen production rate. Steel that is directly immersed in simulated cement pore water requires only months to stabilize. All measured steel uniform corrosion rates were significantly below 1 nm year−1 at 50°C, regardless of the test environment, after more than 4 years of exposure.

Effect of closed and open system freeze–thaw cycles on GMB–GCL interface transmissivity

An experimental study of the effect of closed system and a limited study of open system freeze–thaw cycles on the interface transmissivity at applied stresses between 10 and 150 kPa is described. The effect of closed system freeze–thaw is most apparent after 100 freeze–thaw cycles and permeation at a stress ≤25 kPa. The effect of permeating fluid chemistry is also evident but decreased with increasing stress. One notable effect of permeant is the potential for internal erosion along weaknesses in the bentonite created by freeze–thaw cycles when permeated by distilled or reverse osmosis water. This is not observed when permeated with simulated pore water containing cations. In terms of practical application, closed system freeze–thaw cycles appear to have little effect on interface transmissivity, and to the extent that there is an effect, it is beneficial. In contrast, cryogenic suction arising with open system freeze–thaw cycles is shown to result in the formation of ice lenses both within the geosynthetic clay liner (GCL) and at the GCL geomembrane interface. Although limited, the data suggest that the effect of ice lens formation on interface transmissivity after open system freeze–thaw cycles is largely eliminated at applied stress above 20–25 kPa, although more research is warranted.

New radiolysis-driven matrix dissolution operational model based on stationary UO2 voltametric experiments

In the framework of research on direct deep disposal of spent nuclear fuel, a new α radiolysis-driven matrix dissolution model is proposed. This model is based on an experimental stationary voltametric curve established using a UO2 rotating disk electrode in a neutral pH non-complexing solution under reducing conditions. Kinetic and chemical speciation calculations give access to the equilibrium redox potential of a simulated Callovo-Oxfordian pore water solution containing α-radiolysis products, which is used in the experimentally obtained current-potential relationship to estimate the oxidative dissolution rate. Comparison of model results with literature data show good agreement with previously established α−activity threshold values.

Corrosion Study on Wellbore Materials for the CO2 Injection Process

For reliability and safety issues of injection wells, corrosion resistance of materials used needs to be determined. Herein, representative low-cost materials, including carbon steel X70/1.8977 and low alloyed steel 1.7225, were embedded in mortar to mimic the realistic casing-mortar interface. Two types of cement were investigated: (1) Dyckerhoff Variodur commercial Portland cement, representing a highly acidic resistant cement and (2) Wollastonite, which can react with CO2 and become stable under a CO2 stream due to the carbonation process. Exposure tests were performed under 10 MPa and at 333 K in artificial aquifer fluid for up to 20 weeks, revealing crevice corrosion and uniform corrosion instead of expected pitting corrosion. To clarify the role of cement, simulated pore water was made by dispersing cement powder in aquifer fluid and used as a solution to expose steels. Surface analysis, accompanied by element mapping on exposed specimens and their cross-sections, was carried out to trace the chloride intrusion and corrosion process that followed.

A new test system for unraveling the effects of soil components on the uptake and toxicity of silver nanoparticles (NM-300K) in simulated pore water

Fate, bioavailability and toxicity of silver nanoparticles (AgNP) are largely affected by soil properties. Here we focused on how these processes are connected in simulated soil pore water. OECD soil components (sand, kaolin clay, peat) were covered with NM-300K-, AgNO3- and NM-300K dispersant-contaminated water, and Folsomia candida were exposed on the water surface. After 14 days the majority of AgNP was in nano form in sand pore water where also silver uptake was highest. Multilayered cross sections from X-ray micrographs of Collembola exposed to AgNP showed that silver was located in animal areas of direct contact to the contaminated pore water and was ingested. In contrast, in simulated peat pore water only a small fraction of silver was bioavailable. AgNO3 was only bioavailable at the start of the test and not anymore at test end. AgNP and AgNO3 caused immobilization in sand and kaolin pore water while no toxicity was found with peat and OECD soil. A strong correlation (correlation coefficient = 0.901) existed between the concentration of nano silver and immobilization; for ionic silver this was not the case. The dispersant of AgNP was toxic on its own in sand and kaolin pore water. As there are analytical limitations of quantifying AgNP in complex matrices this test system enables a mechanistic view of exposure and uptake of AgNP (and other substances) by F. candida from soil pore water.

Porewater salinity in a southeastern United States salt marsh: controls and interannual variation.

In coastal marsh ecosystems, porewater salinity strongly affects vegetation distribution and productivity. To simulate marsh porewater salinity, an integrated, spatially explicit model was developed, accounting for tidal inundation, evaporation, and precipitation, as well as lateral and vertical exchanges in both surface waters and the subsurface. It was applied to the Duplin River marsh, Sapelo Island, USA, over a 3-year period, which covered both drought and wet conditions. Simulated porewater salinity in the low and high marsh correlated with Duplin River salinity, with evapotranspiration and precipitation leading to substantial variations in porewater salinities across seasons, in particular in the high marsh. The model revealed substantial interannual variability in marsh soil conditions, and—due to its process-based approach linked to external forcings—can be used to explore effects of sea level rise and changes in hydrological forcings on marsh soil conditions.

Combined effects of tides, evaporation and rainfall on the soil conditions in an intertidal creek-marsh system

Salt marshes, distributed globally at the land-ocean interface, are a highly productive eco-system with valuable ecological functions. While salt marshes are affected by various eco-geo-hydrological processes and factors, soil moisture and salinity affect plant growth and play a key role in determining the structure and functions of the marsh ecosystem. To examine the variations of both soil parameters, we simulated pore-water flow and salt transport in a creek-marsh system subjected to spring-neap tides, evaporation and rainfall. The results demonstrated that within a sandy-loam marsh, the tide-induced pore-water circulation averted salt build-up due to evaporation in the near-creek area. In the marsh interior where the horizontal drainage was weak, density-driven flow was responsible for dissipating salt accumulation in the shallow soil layer. In the sandy-loam marsh, the combined influences of spring-neap tides, rainfall and evaporation led to the formation of three characteristic zones, c.f., a near-creek zone with low soil water saturation (i.e., well-aerated) and low pore-water salinity as affected by the semi-diurnal spring tides, a less well-aerated zone with increased salinity where drainage occurred during the neap tides, and an interior zone where evaporation and rainfall infiltration regulated the soil conditions. These characteristics, however, varied with the soil type. In low-permeability silt-loam and clay-loam marshes, the tide-induced drainage weakened and the soil conditions over a large area became dominated by evaporation and rainfall. Sea level rise was found to worsen the soil aeration condition but inhibit salt accumulation due to evaporation. These findings shed lights on the soil conditions underpinned by various hydrogeological processes, and have important implications for further investigations on marsh plant growth and ecosystem functions.

Chronic ZnO-NPs exposure at environmentally relevant concentrations results in metabolic and locomotive toxicities in Caenorhabditis elegans

ZnO nanoparticles (ZnO-NPs) are emerging contaminants that raise the concerns of potential risk in the aquatic environment. It has been estimated that the environmental ZnO-NPs concentration is 76 μg/l in the aquatic environment. Our aim was to determine the aquatic toxicity of ZnO-NPs with chronic exposure at environmentally relevant concentrations using the nematode Caenorhabditis elegans. Two simulated environmentally relevant mediums—moderately hard reconstituted water (EPA water) and simulated soil pore water (SSPW)—were used to represent surface water and pore water in sediment, respectively. The results showed that the ZnO-NPs in EPA water has a much smaller hydrodynamic diameter than that in SSPW. Although the ionic release of Zn ions increased time-dependently in both mediums, the Zn ions concentrations in EPA water increased two-fold more than that in SSPW at 48 h and 72 h. The ZnO-NPs did not induce growth defects or decrease head thrashes in C. elegans in either media. However, chronic exposure to ZnO-NPs caused a significant reduction in C. elegans body bends in EPA water even with a relatively low concentration (0.05 μg/l); similar results were not observed in SSPW. Moreover, at the same concentrations (50 and 500 μg/l), body bends in C. elegans were reduced more severely in ZnO-NPs than in ZnCl2 in EPA water. The ATP levels were consistently and significantly decreased, and ROS was induced after ZnO-NPs exposure (50 and 500 μg/l) in EPA water. Our results provide evidences that chronic exposure to ZnO-NPs under environmentally relevant concentrations causes metabolic and locomotive toxicities implicating the potential ecotoxicity of ZnO-NPs at low concentrations in aquatic environments.

Real-time monitoring of nitrate transport in the deep vadose zone under a crop field – implications for groundwater protection

Abstract. Nitrate is considered the most common non-point pollutant in groundwater. It is often attributed to agricultural management, when excess application of nitrogen fertilizer leaches below the root zone and is eventually transported as nitrate through the unsaturated zone to the water table. A lag time of years to decades between processes occurring in the root zone and their final imprint on groundwater quality prevents proper decision-making on land use and groundwater-resource management. This study implemented the vadose-zone monitoring system (VMS) under a commercial crop field. Data obtained by the VMS for 6 years allowed, for the first time known to us, a unique detailed tracking of water percolation and nitrate migration from the surface through the entire vadose zone to the water table at 18.5 m depth. A nitrate concentration time series, which varied with time and depth, revealed – in real time – a major pulse of nitrate mass propagating down through the vadose zone from the root zone toward the water table. Analysis of stable nitrate isotopes indicated that manure is the prevalent source of nitrate in the deep vadose zone and that nitrogen transformation processes have little effect on nitrate isotopic signature. The total nitrogen mass calculations emphasized the nitrate mass migration towards the water table. Furthermore, the simulated pore-water velocity through analytical solution of the convection–dispersion equation shows that nitrate migration time from land surface to groundwater is relatively rapid, approximately 5.9 years. Ultimately, agricultural land uses, which are constrained to high nitrogen application rates and coarse soil texture, are prone to inducing substantial nitrate leaching.

Degradation of carbon fiber reinforced polymer from cathodic protection process on exposure to NaOH and simulated pore water solutions

In this research, the degradation behavior of laminated carbon fiber reinforced polymer (CFRP) strip anode in an electrochemical process was evaluated in an alkali electrolyte (NaOH solution) and simulated pore water solution (containing both alkalis and chloride components) so as to simulate CFRP performance in cathodic protection of atmospherically exposed steel-reinforced concrete. Experiments were conducted with three levels of applied current (0, 0.5, and 4 mA) corresponding to current density of 0, 0.77, and 6.15 A/m2 of anode surface, respectively. The degradation behavior and mechanism was investigated by degradation rate measurement, scanning electron microscopy (SEM), X-ray diffraction, and Fourier transform infrared spectroscopy (FTIR). The result showed that in both solutions, an accelerated degradation rate was observed with the increase in the level of applied current. For an applied current of 4 mA, the degradation rate was approximately 12.4 and 13.6 µm/day for NaOH and pore water solutions respectively. SEM micrographs showed that in both the solutions, the degradation to CFRP occurred at the surface and diffused into the polymer through holes. FTIR results showed that for NaOH solution more oxygen-related bonds were observed after ICCP process. This indicates that oxygen produced at the anode caused the oxidization of epoxy polymer in CFRP and resulted in the softening of polymer. In the pore water solution, the decrease in the intensity of C–N bond and the increase in intensity of C–Cl bond showed that chlorine was preferentially produced at the anode instead of oxygen and acted as the main source for CFRP degradation. The breakage of C–N bond caused the epoxy in CFRP to transform into fine powder and subsequent loose the carbon fibers.

A preliminary investigation into the stability of inorganic arsenic species in laboratory solutions simulating sediment pore water

A simple method to preserve arsenic species in simulated pore water was investigated. Synthetic pore water containing high levels of Fe, Mn and S (as sulfide, S 2– ) were synthesized and spiked with different arsenic species. Arsenite [As(III)], arsenate [As(V)], dimethylarsinate [(CH 3 ) 2 AsO 2– , DMA], monomethylarsonate [(CH3)AsO 3 2– , MMA], monothioarsenate(V) species (AsO 3 S 3– ,MTA) and tetrathioarsenate(v) species (AsS 4 3– , TTA) in different combinations were used. Disodium ethylenediamine tetraacetate (EDTA) and temperature was used to preserve speciation. Solutions were analyzed at intervals of one day, week, month and 2 months after preparation. Samples were analyzed by HPLC-ICP-MS using an ion exchange column and ammonium carbonate buffer. Samples containing Fe and Mn spiked with As(III), As(V), DMA,MMAshowed adequate species preservation for two months when EDTA was added. The total As in samples containing Fe,Mn and S 2– was preserved over 60 days however, speciation was not preserved. Samples spiked with synthesized mono - and tetra -thioarsenate(V) species showed immediate degradation of the mono - and tetra -thioarsenic species into unidentified As-S species. The results show that while EDTA may be adequate to preserve As species containing high Fe and Mn concentrations, the combination of EDTA and temperature was not successful in preserving As speciation in samples containing sulfides. KEYWORDS Arsenic speciation, EDTA, HPLC-ICP-MS, thioarsenic species.

Mineral transformation controls speciation and pore-fluid transmission of contaminants in waste-weathered Hanford sediments

Portions of the Hanford Site (WA, USA) vadose zone were subjected to weathering by caustic solutions during documented releases of high level radioactive waste (containing Sr, Cs and I) from leaking underground storage tanks. Previous studies have shown that waste-sediment interactions can promote variable incorporation of contaminants into neo-formed mineral products (including feldspathoids and zeolites), but processes regulating the subsequent contaminant release from these phases into infiltrating background pore waters remain poorly known. In this paper, reactive transport experiments were conducted with Hanford sediments previously weathered for one year in simulated hyper-alkaline waste solutions containing high or low 88Sr, 127I, and 133Cs concentrations, with or without CO2(aq). These waste-weathered sediments were leached in flow-through column experiments with simulated background pore water (characteristic of meteoric recharge) to measure contaminant release from solids formed during waste-sediment interaction. Contaminant sorption–desorption kinetics and mineral transformation reactions were both monitored using continuous-flow and wet-dry cycling regimes for ca. 300 pore volumes. Less than 20% of contaminant 133Cs and 88Sr mass and less than 40% 127I mass were released over the course of the experiment. To elucidate molecular processes limiting contaminant release, reacted sediments were studied with micro- (TEM and XRD) and molecular- (Sr K-edge EXAFS) scale methods. Contaminant dynamics in column experiments were principally controlled by rapid dissolution of labile solids and competitive exchange reactions. In initially feldspathoidic systems, time-dependent changes in the local zeolitic bonding environment observed with X-ray diffraction and EXAFS are responsible for limiting contaminant release. Linear combination fits and shell-by-shell analysis of Sr K-edge EXAFS data revealed modification in Sr–Si/Al distances within the zeolite cage. Wet-dry cycling did not affect significantly molecular-scale transformations relative to continuous-flow controls. Results indicate that contaminants bound to the solid phase in distinct micro- and molecular-scale coordinative environments can generate similar macro-scale release behaviors, highlighting the need for multi-scale interrogations to constrain mechanisms of reactive transport. Data also indicate that weathering-induced change in ion exchange selectivity coefficients should be incorporated in simulations of contaminant release from caustic high-level radioactive waste impacted sediments.

Instability of a geogrid reinforced soil wall on thick soft Shanghai clay with prefabricated vertical drains: A case study

A 7.6 m high geogrid reinforced soil retaining wall (RSW) was constructed at the end of an embankment on very thick, soft Shanghai clay with 12 m deep prefabricated vertical drains (PVDs). The settlement of the ground, the wall movement and pore water pressure were monitored during the construction. From day 118, halfway through the construction, unexpected pore water pressure increment was recorded from the pore water pressure meters installed in the PVD drained zone indicating a possible malfunction of the PVDs due to large deformation in the ground. After the last loading stage, on day 190, a sudden horizontal movement at the toe was observed, followed by an arc shaped crack on the embankment surface at the end of the reinforced backfill zones. The wall was analyzed with a coupled mechanical and hydraulic finite element (FE) model. The analysis considered two scenarios: one with PVDs fully functional, and the second one with PVD failure after day 118 by manually deactivating the PVDs in the FE model. The comparison between the measured and simulated ground settlement, toe movement, and pore water pressure supported the assumption on the malfunction of the PVDs. It is believed that the general sliding failure in the wall was caused by the increase of pore water pressure in the foundation soil and soils in front of the toe. It is suggested that possible failure of PVDs should be considered in the design of such structures, and the discharge rate of the PVDs and the pore water pressure should be closely monitored during the construction of high soil walls on soft soils to update the stability of the structures, especially for grounds where large deformations are expected which may cause the failure of the PVDs.

Colloid mobilization in an undisturbed sediment core under semiarid recharge rates

The semiarid US Department of Energy Hanford site has a deep vadose zone with low recharge rates. Contaminants originating from nuclear waste processing are expected to move slowly through the vadose zone. The movement of certain contaminants can be facilitated by colloids. We hypothesized that the low recharge rates and low water contents in semiarid regions, however, tend to inhibit movement of colloidal particles, thereby reducing the risk for colloid‐facilitated contaminant transport. The goal of this study was to investigate whether in situ natural colloids can be mobilized and transported in undisturbed, deep vadose zone sediments at the Hanford site under typical, semiarid recharge rates. We sampled an undisturbed sediment core (i.d. 50 cm, 59.5 cm height) from a depth of 17 m below ground at the Hanford 200 Area. The core was set up as a laboratory lysimeter and exposed to an infiltration rate of 18 mm/yr by applying simulated pore water onto the surface. Particle concentrations were quantified in the column outflow, and selected samples were examined microscopically and for elemental composition (transmission electron microscopy and energy dispersive X‐ray). Measured water contents and potentials were used to calibrate a numerical model (HYDRUS‐1D), which was then applied to simulate colloid mobilization from the sediment core. During 5.3 years of monitoring, natural colloids like silicates, aluminosilicates, and Fe‐oxides were observed in the core outflow, indicating the continuous mobilization of in situ colloids. The total amount of particles mobilized during 5.3 years corresponded to 1.1% of the total dispersible colloids inside the core. Comparison of the amounts of colloids released with weathering rates suggests that mineral weathering can be a major source of the mobilized colloids. The fitted colloid release rate coefficient was 6 to 7 orders of magnitude smaller than coefficients reported from previous studies, where disturbed Hanford sediments and higher flow rates were used. Our findings demonstrate that even under low recharge rates and water contents typical for semiarid, deep vadose zone sediments, particles can continuously be mobilized, although the total mass of particles is low.

Evaluation of chemical parameters and ecotoxicity of a soil developed on gossan following application of polyacrylates and growth of Spergularia purpurea

The aim of this study was to evaluate the chemical characteristics and ecotoxicity of a mine soil developed on gossan materials and amended with hydrophilic polyacrylate polymers after a growth cycle of Spergularia purpurea. Different acute bioassays (Daphnia magna immobilization; microalgae growth inhibition; germination and growth of lettuce and oat) were carried out with simulated leachates, pore water and soil samples. The germination and growth of native shrubs (Cistus ladanifer and Lavandula sampaioana) were also evaluated in the lysimeters where S. purpurea had grown.The soil had high total concentrations (g/kg) of Al (3.50–8.60), As (2.55–2.73), Cu (0.13–0.91) and Pb (4.48–6.16). However, the percentages of elements in aqueous extracts (simulating leachates, pore water, and the conditions of the rhizosphere soil) were small when compared to their total soil concentrations (less than 9% except for Na in leachates). Growth of S. purpurea and other natural colonization of plant species (Poaceae, Fabaceae and Asteraceae families) improved chemical characteristics but the application of the polyacrylate polymers contributed to a further improvement of soil quality. However, this was not sufficient to ensure the growth of a large number of shrubs despite a great germination rate.Among the several species used on the ecotoxicological assessment, the D. magna test was the only bioassay that showed a clear toxicity of soil leachates, suggesting the importance of using several ecotoxicological tests to assess the environmental risk of soil contamination and its rehabilitation.Although the studied soil can be considered contaminated taking into account the total soil concentrations of Al, As, Cu and Pb, the low concentrations of the same chemical elements in extractable solutions, that simulated the fractions really available for organisms, did not demonstrate a substantial toxic effects in the organisms and, consequently, negative impact on the environment.

The anaerobic corrosion of carbon steel in alkaline media – Phase 2 results

In the Belgian Supercontainer concept a carbon steel overpack will surround high-level waste and spent fuel containers and be encased in a cementitious buffer material. A programme of research was carried out to investigate and measure the rate of anaerobic corrosion of carbon steel in an artificial alkaline porewater that simulates the aqueous phase in the cementitious buffer material. The corrosion rates were measured by monitoring hydrogen evolution using a manometric gas cell technique and by applying electrochemical methods. Phase 2 of the programme has repeated and extended previous Phase 1 measurements of the effects of radiation, temperature and chloride concentration of the anaerobic corrosion rate. This paper provides an update on the results from Phase 2 of the programme. The results confirm previous conclusions that the long-term corrosion rate of carbon steel in alkaline simulated porewater is determined by the formation of a thin barrier layer and a thicker outer layer composed of magnetite. Anaerobic corrosion of steel in cement requires an external supply of water.

Surface micro‐topography causes hot spots of biogeochemical activity in wetland systems: A virtual modeling experiment

Wetlands provide important ecohydrological services by regulating fluxes of nutrients and pollutants to receiving waters, which can in turn mitigate adverse effects on water quality. Turnover of redox‐sensitive solutes in wetlands has been shown to take place in distinct spatial and temporal patterns, commonly referred to as hot spots and hot moments. Despite the importance of such patterns for solute fluxes the mechanistic understanding of their formation is still weak and their existence is often explained by variations in soil properties and diffusive transport only. Here we show that surface micro‐topography in wetlands can cause the formation of biogeochemical hot spots solely by the advective redistribution of infiltrating water as a result of complex subsurface flow patterns. Surface and subsurface flows are simulated for an idealized section of a riparian wetland using a fully integrated numerical code for coupled surface‐subsurface systems. Biogeochemical processes and transport along advective subsurface flow paths are simulated kinetically using the biogeochemical code PHREEQC. Distinct patterns of biogeochemical activity (expressed as reaction rates) develop in response to micro‐topography induced subsurface flow patterns. Simulated vertical pore water profiles for various redox‐sensitive species resemble profiles observed in the field. This mechanistic explanation of hot spot formation complements the more static explanations that relate hot spots solely to spatial variability in soil characteristics and can account for spatial as well as temporal variability of biogeochemical activity, which is needed to assess future changes in the biogeochemical turnover of wetland systems.

Thermohydromechanical modelling of the buffer/container experiment

In order to investigate how heat affects the performance of a dense bentonite–sand buffer material, a full-scale in situ experiment, the Buffer/Container Experiment (BCE), was conducted by Atomic Energy of Canada Limited (AECL). In the BCE, an electric heater simulating the heat output of a disposal container of used fuel was installed vertically in a 1.24-m-diameter by 5-m-deep borehole surrounded by bentonite–sand buffer. The borehole was drilled in the floor of a room excavated in Canadian Shield granite on the 240 Level of AECL's Underground Research Laboratory (URL). The thermal, hydraulic and mechanical responses were monitored in the bentonite–sand buffer and in the surrounding rock. Power was provided to the heater for approximately 896 days. In order to get a better understanding of the coupled thermohydromechanical (T-H-M) process in the BCE, numerical simulations were conducted using CODE_BRIGHT to model the evolution of the temperature, thermally induced pore water pressure and mechanical response in the bentonite–sand buffer and the surrounding rock. The thermal response in the experiment was successfully modelled. The simulated water seepage from the rock to the borehole was compared with measured results for the BCE. The thermally induced moisture movement in the buffer was also reasonably well simulated. The comparison of the simulated pore water pressure in the rock with the measurement indicates that the influence of temperatures on the hydraulic parameters of rock should be further studied. The modelled vertical displacements in the rock are also compared with the measured data in the BCE and the analysis of the rock displacement suggested that the in situ thermal expansion coefficient of the rock could be much higher than the coefficient determined in the laboratory.

Further studies on the effect of irradiation on the corrosion of carbon steel in alkaline media

This paper summarises recent experimental results from a programme that was carried out to investigate the effects of radiation on the anaerobic corrosion of carbon steel, in relation to the overpack that will be used in the Belgian supercontainer concept for radioactive waste disposal. Anaerobic corrosion rates of carbon steel were measured by monitoring hydrogen evolution using manometric gas cells and an autoclave and the corresponding electrochemical behaviour was investigated by measuring open circuit potential, linear polarisation resistance and alternating current impedance. The test medium was alkaline simulated pore water, at γ-irradiation dose rates of 0 and 25 Gy h−1, temperatures of 25 and 80°C and chloride concentrations of 0 and 100 mg L−1. The anaerobic corrosion rates exhibited a slow decline due to the formation of magnetite. Good agreement was found with weight loss measurements. A dose rate of 25 Gy h−1 had a negligible effect on gas generation rates.