Simulated Underground Water Research Articles

Binderless and Oxygen Vacancies Rich FeNi/Graphitized Mesoporous Carbon/Ni Foam for Electrocatalytic Reduction of Nitrate.

Energy consumption and long-term stability of a cathode are two important aspects of great concern in electrocatalytic nitrate reduction. This work studied a binderless FeNi/graphitized mesoporous carbon directly formed on Ni Foam (FeNi/g-mesoC/NF, 7.3 wt % of Fe) and evaluated its electrocatalytic nitrate reduction performance. We proposed a unique structure model of FeNi/g-mesoC/NF cathode in which FeNi alloy nanoparticles were uniformly embedded in mesoporous carbon and graphitized carbon shells were coated on isolated alloy nanoparticles. Oxygen vacancies (OVs) in FeNi oxide passivating layer facilitate the conversion of NO3--N anions on cathode. Toxic NO2--N was almost undetected due to the synergetic effects of FeNi electrocatalysis, and the NO3--N conversion was high in comparation with ever reported iron-based cathode. The NO3--N conversion showed ultrahigh electrocatalytic stability during one-month-recycling test while the physiochemical properties showed negligible change for FeNi/g-mesoC/NF except the increase of OVs. The energy consumption to treat simulated underground water (50% of NO3--N conversion) was low (0.7 kWh mol-1) for 50 mg L-1 NO3--N. This binderless composite cathode shows great potential in electrocatalytic NO3--N removal in underground water.

Long term corrosion estimation of carbon steel, titanium and its alloy in backfill material of compacted bentonite for nuclear waste repository

The container of high-level radioactive waste (HLRW) being in deep geological disposal, the backfill material is needed to serve as the second defense for HLRW and the highly compacted bentonite is generally selected. As the time goes, the underground water will infiltrate the backfill, causing the corrosion of materials for the building of containers in the formed electrolyte. Carbon steel, titanium and its alloy are the potential candidate materials for the fabrication of HLRW containers. The current investigation aims at assessing the safety of HLRW container in deep geological disposal for hundreds of thousands of years and facilitating the material selection for future container fabrication by estimating their corrosion behavior in compacted bentonite with a series of moisture content at different temperatures through electrochemical methods including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve (PC) measurements. The corrosion rates were estimated for a carbon steel, a pure titanium and a titanium alloy in compacted Gaomiaozi Bentonite infiltrated with simulated underground water in Beishan area of China over an expected disposal period up to 106 years respectively, showing that titanium and its alloy are more reliable materials for building HLRW containers than carbon steel.

Activity Reduction of 232Th and 40K from Simulated Underground Water Using a Clay-Based Membrane

In this research, the activities of 232Th and 40K in simulated underground water were reduced using inexpensive clay-based membrane. Starch (10 and 15 wt%) was added to the clay, compacted and fired up to 1300°C to produce the porous membranes. The characterization of the raw clay and the produced membranes was conducted using XRF, XRD, TGA/DTA, BET and FESEM. The activities of 232Th and 40K in the waste and permeated water were counted using gamma spectroscopy. The produced membranes were having pore sizes in the range 39.68-46.10nm; from the BET isotherm, it shows the membranes produced are mesoporous. Also, the steady flux of the filtered water was found to be in the range 3.83×10-7-1.77×s10-6 m3m-2s-1. Activities of thorium and potassium in the permeated water were found to be 4.57-5.61 Bq/l and 15.49-25.19 Bq/l respectively. This shows that inexpensive clay can be used to reduce the activities of thorium and potassium in underground water from mining, fracking and produced water from oil and gas.

Corrosion behaviour of carbon steel, titanium and titanium alloy in simulated underground water in Beishan area preselected for nuclear waste repository in China

ABSTRACTThe groundwater will completely infiltrate to the surface of nuclear waste container after the closure of its deep geological disposal. Therefore, the corrosion behaviour of Q235 carbon steel, titanium and titanium alloy, which were the candidates as the container materials for high-level nuclear waste disposal in simulated groundwater solution of Beishan to be served as the preselected high-level nuclear waste disposal area in China at different temperatures, was studied through electrochemical methods including open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarisation curve measurements. The results show that the corrosion rate of titanium and titanium alloy is lower than that of carbon steel at all temperatures, and they are more promising as container materials. Another phenomenon is that higher temperatures facilitate the protection performance of corrosion products compared with lower temperatures.

Mechanistic Aspect of Non-Steady Electrochemical Characteristic During Stress Corrosion Cracking of an X70 Pipeline Steel in Simulated Underground Water

The stress corrosion cracking (SCC) and the electrochemical behavior of an API X70 pipeline steel in a simulated acidic soil solution were investigated using slow strain rate testing (SSRT), electr...

Stress Corrosion Cracking of Welded API X70 Pipeline Steel in Simulated Underground Water

This paper investigates the stress corrosion cracking (SCC) behavior of welded API X70 pipeline steel in simulated underground water using the slow strain rate test, fractographic characterization by scanning electron microscopy, and potentiodynamic polarization techniques. SCC susceptibility of the heat-affected zone (HAZ) is demonstrated to be dependent on two factors: the effect of the microstructure in the HAZ on electrochemical reactions and the effect of the mechanical property on SCC occurrence. Electrochemical experiments indicate that the microstructures in the HAZ, especially the softened microstructure, can significantly facilitate the processes of hydrogen evolution when cathodic potential is positive to −1050 mVSCE. However, when the cathodic potential is below −1050 mVSCE, the cathode current densities of different microstructures are close to one another and greatly increase because of the decrease of the applied potentials. The SCC behavior is consistent with the electrochemical results. Under −650 and −850 mVSCE, SCC is most likely to occur in the softened region, and under −1200 mVSCE, SCC occurs in both the softened and hardened regions.

Development of a durable fiber-optic oxygen sensor for harsh underground environments

This paper focuses on effects of protection with a silicone resin to develop a fiber-optic oxygen sensor with long-term stability and durability in harsh underground environments. Ruthenium (II) complexes were used as oxygen-sensing compounds. A uniform composite film composed of silicone resin and the Ru complex was prepared with spin coating technique. A comparison of dissolved-oxygen (DO) sensitivity between the composite film and a Ru complex film was made by exposing to hot water (80 °C). The result of the accelerated degradation test showed that sensitivity of the Ru complex film was stable; meanwhile that of the composite film increased with exposure time in a short period. In order to improve stability, the Ru complex film overcoated with silicone resin was prepared. Differences in sensitivity for saturated DO (8.5 ppm) between with and without the silicone resin overcoating on the Ru complex film were investigated by exposing to the hot water and simulated underground water. These results revealed that the sensitivities and response times of the overcoated films were stable and slow, respectively, compared to those of non-overcoated films. Then, optodes were evaluated for effects of the overcoating on sensing properties by exposing to 100 vol.% oxygen gas. The experiment showed that: (1) the response time was significantly influenced by the thickness of the overcoating; and (2) response speed of the overcoated optode was slow by a factor of about 35 compared to that of the non-overcoated. We concluded that the overcoating was effective in the application to mid- and long-term oxygen monitoring in the harsh environments.

Modeling the leaching behavior of simulated HLW-glass using PHREEQC

PHREEQC is a geochemical model to study aqueous ion reaction equilibrium in water systems. In this paper, PHREEQC was used to calculate concentrations of main elements (Si, Na, B, Al, Sr, Cs, Fe and Nd) leached from simulated HLW-glass in solution. The experiments were preformed in deionized-water or simulated underground water at 90 °C or 150°C under low oxygen atmosphere. The calculated results agreed well with the experimental results.

Temperature Effects on the Leaching Behavior of a High-Level Waste Glass Form

Temperature has strong effects on the leaching behavior of the 90-19/U simulated high-level waste glass form. The Arrhenius equation is used to determine the change in the glass corrosion mechanism throughout the different temperature ranges. The apparent activation energies have been obtained for different leaching conditions. In deionized water, the glass corrosion mechanism is similar whether the leaching condition is static or dynamic. The glass corrosion process is dominated by the ion exchange reactions at lower temperatures (≤60 to ~70°C); however, the glass corrosion process is dominated by the network hydrolysis reactions at higher temperatures (>70°C). The apparent activation energy in the lower temperature range is larger than that of the higher temperature range. In simulated underground water, the ion exchange reactions dominated the glass corrosion mechanism at temperatures from 50 to 150°C, and the large amount of ions in simulated underground water would participate in the ion exchange reactions with the glass.

Sintered Glasses for High-Level Wastes

ABSTRACTThe objective of the work was to evaluate the long-term capacity of sintered glass to retain high-level nuclear wastes (HLW) in near-repository conditions. We have studied the corrosion behavior of waste forms partially devitrified (43 vol.%) in different aqueous media. Devitrified samples were irradiated at doses (γ radiation from a Co 60 source) ranging from 1.4 × 106 Gy to 2.0 × 108 Gy, in order to study their aqueous corrosion resistance in simulated underground water. The results show little or no effect of irradiation on the density, microstructure and corrosion resistance. The global dissolution rate was almost constant around a value of 5×10−5 g. cm−2 d−1. Elemental dissolution rates were also unaffected by radiation.