Hydrogen isotopes separation using frontal displacement chromatography with Pd–Al2O3 packed column

Separation or purification of tritium isotopes is one of the key technologies in ITER. A set of frontal displacement chromatography (FDC) device was designed and constructed for hydrogen isotopes separation using palladium loading on/in alumina (Pd–Al₂O₃) as the separation material. The hydrogen isotopes separation experiments were carried out. It was found that deuterium abundance of the product was up to 98.5% and the average separation factor was as high as 64, under the condition of 273 K column temperature and 15 mL(NTP)/min flow rate, for a feed gas of 5%H₂-5%D₂-90%Ar. The deuterium recovery ratio was 42% in this separation test. The results showed that the separation performance of our FDC device was good by using Pd–Al₂O₃ as separation materials, and it suggested considerable potential for the applicability of FDC in hydrogen isotopes separation.     

Hydrogen isotopes separation using frontal displacement chromatography: The influences of column temperature and gas flow rate

Based on the previous study in frontal displacement chromatography (FDC) packed with Pd-Al₂O₃, two groups of separation experiments were conducted to derive the rules how the two most significant factors, temperature and gas flow rate, to influence the separation performance. Separations of the first group were carried out at the feed gas flow rate of 15 mL/min and temperature of 303–213 K, and the second group at 253 K and 10–100 mL/min, with the identical composition of feedstock ((5 ± 0.1)%H₂-(5 ± 0.1)%D₂-(90 ± 0.1)%Ar). The results indicate the derived rules are consistent with those from references: 1) the rules of temperature effects on separation efficiency lie in two aspects that the lower the temperature is, the larger the thermodynamic separation effect is, and the higher the temperature is, the quicker the hydrogen isotopes exchange dynamics becomes. As to FDC using palladium, 263–213 K will be an appropriate temperature range to have excellent separation performance achieved with the insight into these two aspects. 2) the rule of the influence of gas flow rate basically obeys the van Deemter equation, which means that it does exist an theoretically optimal gas flow rate, ū_opt, at a certain temperature and for a certain composition of feedstock, and considering the theoretics and efficiency, separations conducted at the gas flow rate of an suitable range that higher than ū_opt but less than 10ū_opt can derive good separation performance. The results and discussion have verified the imperative impact of temperature and gas flow rate on the separation performance of this FDC method, and the derived desirable temperature and gas flow rate ranges would supply valuable supports and references for future applications of FDC in hydrogen isotopes separation and tritium recovery in fusion reactors.     

The isothermal sorption behaviour of aged palladium tritide

Experiments to investigate changes in the sorption behaviour of palladium when aged as β-palladium tritide for a 5.6 year period have been undertaken. The palladium was found to retain a significant quantity of the ³He generated by the decay of tritium (³He/Pd = 0.15) which modified the sorption behaviour. The observations corroborate previous reports of a shift in the α-phase boundary to higher compositions, a lowering of the plateau pressures and some tritium becoming trapped within the aged material. In contrast to previous work, no age related slope in the plateau pressures was observed and the trapped tritium was found to lower the stoichiometry of the β-phase boundary.     

The rate of an exchange reaction of hydrogen and deuterium in a Mg2Ni bed

Hydrides of intermetallic compounds of Mg₂Ni have a comparatively large isotopic effect in the equilibrium isotherm between hydrogen and deuterium or tritium. An experimental and analytical study is made on the isotopic exchange reaction of hydrogen and deuterium in a Mg₂Ni bed for isotope separation. Values of the first moment, the second moment and a height equivalent to a theoretical plate (HETP) are obtained on the basis of a pulse or a step change of an influent deuterium concentration. It is found that the HETP values have the least at an optimum temperature and linear velocity, and the value is about 3 cm. The activation energy of the isotopic exchange reaction of Mg₂Ni is 18.5 kJ mol⁻¹. Thus the Mg₂Ni bed serves as an effective method for the isotopic separation of hydrogen isotopes.     

Protium removal from deuterium-tritium mixture with displacement chromatography method: Experiments and simulations

The displacement chromatography technique with a tri-column system was used to reduce the protium (H) in the deuterium-tritium (D-T) mixture, and the separation performance was studied numerically by ANSYS FLUENT. The experimental results showed that the isotopic abundance of H in the D-T mixture dropped from 2.7% to an acceptable level of 0.88%. The simulation results showed that a lower porosity (θ) of the filling material made a higher separation factor, but a lower separation efficiency. The velocity of the product gas at the outlet of the separation column approximately had a linear relationship with θ^5/3/(1-θ)², which partly indicated the pore diffusion resistance. The mixed gas could contact the filling materials more sufficiently under a lower flow rate resulting in a lower protium concentration in the product gas. The separation column with a thin and long shape had a better separation performance and a lower product gas loss.     

Hydrogen isotopes separation validation of frontal displacement chromatography for various compositions of feed gas and tritium extraction simulation for TBM

Based on the previous study in frontal displacement chromatography (FDC) packed with Pd-Al₂O₃, three groups of separation tests were carried out to verify the separation performance of the constituted FDC device for various compositions of feed gas and to validate the application probability of FDC in the Tritium Extraction System (TES) of ITER and China Fusion Engineering Test Reactor (CFETR). The separations were conducted by the FDC procedure with characteristics of the feed gas one-time flushing though the column and then reasonable separation performance had been obtained. The results indicate that the FDC process could be applied to deal with the desorbed gas mixtures from TES and/or further to extract and thereafter enrich the breeding tritium in ITER or CFETR, which would take the advantages of system compactness and efficiency over the present route of TES. Comparing to other related displacement chromatography procedures, the FDC process could be applied in tritium pre-enrichment for the mixtures of low tritium concentrations, which is highlighted by the outstanding merit of operation simplicity.     

Palladium composite membrane fabricated on rough porous alumina tube without intermediate layer for hydrogen separation

A thin palladium composite membrane without any modified layer was successfully obtained on a rough porous alumina substrate. Prior to the fabrication of palladium membrane, a poly(vinyl) alcohol (PVA) layer was first coated onto the porous substrate by dip-coating technique to improve its surface roughness and pore size. After deposition of palladium membrane on the PVA modified substrate, the polymer layer can be completely removed from the composite membrane by heat treatment. The microstructure of the palladium composite membrane was characterized in detail using SEM, EDXS and XRD analysis. Permeation measurements were carried out using H₂ and N₂ at temperatures of 623 K, 673 K, 723 K and 773 K. The results indicated that the hydrogen permeation flux of 0.238 mol m^?2 s^?1 with H₂ separation factor α(H₂/N₂) of 956 for the as-prepared palladium membrane was obtained at 773 K and 100 kPa. Furthermore, the good membrane stability was proven during the total operation time of 160 h at the temperature range of 623 K–773 K and gas exchange cycles of 30 between hydrogen and nitrogen at 723 K.     

Hydrogen isotope permeation through yttria coatings on Eurofer in the diffusion limited regime

In fusion power plants a tritium permeation barrier is required in order to prevent the loss of the fuel. Moreover, the tritium permeation barrier is necessary to avoid that the radioactive tritium accumulates in the first wall, the cooling system, and other parts of the power plant. Oxide thin films, e.g. Al₂O₃, Er₂O₃ and Y₂O₃, are promising candidates as tritium permeation barrier layers. With regard to the application, this is especially true for yttrium due to its favorably short decay time after neutron activation compared to the other candidates. The Y₂O₃ layers with thicknesses from 100 nm to 500 nm are deposited on both sides of Eurofer substrates by RF magnetron sputter deposition. Some of the samples are additionally deposited with palladium thin films to analyse the limited regime. During the annealing in the experiments the palladium layers do not show any crack formation or delamination, verified by scanning electron microscopy. After annealing the cubic crystal structure of the Y₂O₃ layers is verified by X-ray diffraction. The cubic phase contains a small amount of a monoclinic phase, which is eliminated after the permeation measurements. The permeation reduction factors of the samples are determined in gas-driven deuterium permeation experiments. A permeation reduction of 5000 of the yttria thin film is verified. The diffusion limited regime is identified by the pressure dependence of the permeation measurement and by permeation experiments with the palladium top layers on the Y₂O₃ thin films. Furthermore, the activation energy of the permeation through the yttria thin films is determined. Pre-annealing times for more than 70 h of the Y₂O₃ thin films and permeation measurements with temperature cycles for 20 days are performed to show the stability of the permeation flux and hence the microstructure of the barrier layers. Measurement times at each constant temperature level of more than 25 h are required for the stabilization of each permeation flux to a constant value. The permeation measurement setup is enhanced to enable a continuously running equipment for these measurement times.     

Hydrogen isotope effect of nanoporous palladium

Materials used in hydrogen isotopes separation are crucial in modern hydrogen energy field. In this article, a promising material nanoporous palladium was prepared and its relative properties were studied. Nanoporous palladium with pore scale of about 5 nm was fabricated by free dealloying corrosion. Its kinetic and PCT curves of hydrogen/deuterium adsorption at room temperature were tested using a Sievert-type volumetric apparatus. Microstructures were observed with Scanning Electron Microscopy and Atomic Force Microscopy. Crystalline structure was characterized with X-Ray Diffractometer before and after deuterium adsorption. Comparative experiments with spongy palladium that is commonly used in relative industry were also carried out. According to the results, nanoporous palladium shows faster hydrogen/deuterium adsorption rate than spongy palladium, which is due to its nanoporous structure that supplies a large amount of specific surface area. PCT curves of hydrogen/deuterium adsorption in nanoporous palladium among 298–338 K were tested and plateau pressures at different temperatures were obtained. Deuterium/hydrogen isotopes separation factors were calculated using plateau pressures above and were plotted with temperature. It's found that nanoporous palladium shows larger hydrogen isotope separation factors compared with spongy palladium at temperatures no higher than 323 K. These findings illustrate that nanoporous palladium would be an ideal material for hydrogen isotopes separation applications.     

Role of lattice oxygen in the partial oxidation of methane over Rh/zirconia-doped ceria. Isotopic studies

Isotopic tracer and nuclear reaction analysis (NRA) are used to probe the identity of oxygen for CO formation during the catalytic partial oxidation (CPOX) of methane to synthesis gas on ¹⁸O₂ labeled Rh (1 wt.%)/(Ce_0.56Zr_0.44)O_2−x. Results reveal that methane is selectively oxidized by lattice oxygen ions from the catalyst to form carbon monoxide. ¹⁸O₂ isotopic exchange experiments, as a function of temperature in the 0–850 °C range, were performed on Rh (1 wt.%)/(Ce_0.56Zr_0.44)O_2−x, and (Ce_0.56Zr_0.44)O_2−x. It was observed that the presence of rhodium considerably accelerates the oxygen exchange with the support; the maximal exchange rates could be observed at lower temperatures, 250 °C. This may be due to oxygen spillover from the metal particles to the oxide. Comparing results from the isotopic exchange experiments on Rh/γ-alumina and Rh (1 wt.%)/(Ce_0.56Zr_0.44)O_2−x. It was revealed that oxygen conducting materials have a much higher oxygen storage capacity and isotopic exchange rate than non-oxygen conducting materials.     

Double-sided wet fabric evaporator utilizing wind and solar energy efficiently — One-dimensional transient simulations

The performance of the double-sided fabric seawater evaporator suggested by Nosoko et al. (Desalination and Water Treatment16 (2010) 254) was simulated for a sunny day under subtropical and maritime climate conditions by a one-dimensional transient modeling. The concentration of seawater increases exponentially with the downstream distance along the fabric while the temperature and the evaporation rate increase gradually. In a polyester fabric, seawater flows fast and the concentration of the effluent brine is kept constant in a small range by adjusting the rate of influent seawater according with the solar radiation. In a cotton fabric, seawater flows slow, causes a large time lag between the influent and effluent, and thus varies the effluent concentration greatly. The temperature and evaporation rate of the polyester are approximately the same as those of the cotton. The daily evaporation is 9.41 kg/day ⋅ m² − fabric under a solar radiation of 27.6MJ/m². Lumped capacitance model (Desalination and Water Treatment16 (2010) 254) was found to predict quite accurately the averages of the evaporation rate and temperature of fabric, but to fail in prediction of the temporal variations of the effluent concentration.     

18O/16O isotope exchange for yttria stabilised zirconia in dry and humid oxygen

The oxygen surface kinetics and mechanism of oxygen interaction between oxygen from the gas phase and yttria-stabilised zirconia nano-sized powder have been studied by pulse ¹⁸O/¹⁶O isotope exchange (PIE) in dry (O₂) and humid (mixture O₂ + H₂O with pH₂O = 2.6 kPa at T = 22 °C) oxygen atmospheres in comparison with micro-sized powder. Dependences of the heterogeneous oxygen exchange rate (r_H) in the temperature range from 550 to 900 °C, and oxygen partial pressure range in the carrier gas and pulses of 5–19% have been obtained. It has been established that the presence of water causes a decrease in the heterogeneous oxygen exchange rate due to the presence of strongly bound hydroxyl groups in the nanopores of the sample. Differences between the mechanisms of isotopic exchange for dry and humid atmospheres have been found in this temperature range (550–700 °C). The observed differences are associated with the interaction of the gas phase and hydroxyls in the adsorbed layer of the oxide. An original method for the separation of the contributions of three types of oxygen exchange for dry and humid atmospheres has been proposed.     

Microwave-assisted one-pot hydrothermal synthesis of V and La co-doped ZnO/CNTs nanocomposite for boosted photocatalytic hydrogen production

In this work, vanadium and lanthanum co-doped ZnO/CNTs (VL-ZnO/CNTs) composites of large surface area and enhanced light assimilation range were produced for boosted hydrogen evolution from water. The photocatalysts were investigated for their morphological, structural, optical and photocatalytical properties. The photocatalytic activity of the composites was evaluated in pure water and in a mixture of water and methanol under simulated sunlight and visible light illumination. Under simulated sunlight irradiation, the maximum hydrogen generation rate of 925 μmolh^?1g^?1 from a combination of water and methanol was attained, which is almost 7 times higher than hydrogen generation rate achieved with pure ZnO. The VL-ZnO/CNTs photocatalyst resulted in hydrogen production rate of 267 μmolh^?1g^?1 from the water-methanol medium when exposed to visible light. This rate was about 3.5 folds lower than that achieved under simulated sunlight illumination. This improvement in hydrogen production rate is attributed to large surface area, high photo-response, better separation/transportation of the charge carriers and synergistic impact of V, La and CNTs in the designed photocatalyst.     

Oxygen isotopic ratios of sulfate ions-water pairs as a possible geothermometer

In this paper a brief review is given of the dependence of the oxygen isotopic fractionation of the sulfate ions-water system on temperature and the pH. From the available experimental data some relationships have been elaborated, which show that the isotopic exchange time is strongly temperature and pH dependent. The times for 97 per cent of isotopic exchange (near equilibrium conditions) at pH 7.0 are about 9 years at 200°C and 0.6 years at 330°C, while at pH 3.8 and at the same temperatures the times of exchange are 1.5 years and 0.08 years respectively. Thus, at the temperatures and pH of geothermal reservoirs the sulfate could be in isotopic equilibrium with environmental water, and the oxygen isotopic fractionation factors of sulfate-water geothermal pairs, being temperature dependent, can be used as geothermometers.Also reported here are some results on the O¹⁸ content of sulfate-water pairs from some wells on the edge of and outside the Larderello geothermal basin. The estimated isotopic temperatures are not very significant for the deep reservoir temperatures due to the geological features of the Larderello area which show important outcropping and deep anhydrite layers. Furthermore, as regards the wells outside the Larderello basin (Travale wells) some mixing of the geothermal water with colder underground water has been proved. However, the isotopic temperatures are generally higher than those measured at the well-head, and the highest ones are close to those estimated for the geothermal reservoir.In other geothermal areas more convenient from a geological point of view, the O¹⁸ content of the sulfate-water pair can be a useful and accurate thermometer.The O¹⁸/O¹⁶ ratios of several other sulfates (surface and deep anhydrite samples, sulfate ions in thermal springs) from the same area were also determined and differ substantially from borehole sulfate values.     

Investigation on thermal management performance of wedge‐shaped microchannels for rectangular Li‐ion batteries

The performance of power battery is a significant factor affecting the overall quality of electric vehicles. To optimize the thermal management effect of battery pack, cold plate with wedge‐shaped microchannels was proposed in this paper. On the basis of the models of the independent cold plate and the battery‐cooling module, the effects of outlet aspect ratio, flow rate, and branching structure on the heat dissipation performance of the cold plate were studied at first. Afterwards, the effects of cooling surface, flow rate, and branching structure on the temperature distribution of the battery module were simulated. The results showed that the wedge‐shaped channels provided a good cooling efficiency and surface temperature uniformity. When the wedge‐shaped channel was used in thermal management of the battery module, the side‐cooling method reduced the temperature difference of batteries by more than 35.71% compared with front cooling under the mass flow rate of 2 × 10^?5 kg/s. At a discharge rate of 3.5 C, the flow rate of 1 × 10^?4 kg/s controlled the battery temperature to within 45°C, and the branching structure designed for the module successfully decreased the maximum temperature difference from 7.27°C to 4.67°C, which has been reduced by approximately 35.78%.     

Performance of carbon-supported PtPd as catalyst for hydrogen oxidation in the anodes of proton exchange membrane fuel cells

In this work, the replacement of platinum by palladium in carbon-supported catalysts as anodes for hydrogen oxidation reaction (HOR), in proton exchange membrane fuel cells (PEMFCs), has been studied. Anodes with carbon-supported Pt, Pd, and equiatomic Pt:Pd, with various Nafion^® contents, were prepared and tested in H₂|O₂ (air) PEMFCs fed with pure or CO-contaminated hydrogen. An electrochemical study of the prepared anodes has been carried out in situ, in membrane electrode assemblies, by cyclic voltammetry and CO electrooxidation voltammetry. The analyses of the corresponding voltammograms indicate that the anode composition influences the cell performance. Single cell experiments have shown that platinum could be replaced, at least partially, saving cost with still good performance, by palladium in the hydrogen diffusion anodes of PEMFCs. The performance of the PtPd catalyst fed with CO-contaminated H₂ used in this work is comparable to Pt, thus justifying further work varying the CO concentration in the H₂ fuel to assert its CO tolerance and to study the effect of the Pt:Pd atomic ratio.     

Study of tritium transport characteristics in a transportable fluoride‐salt‐cooled high‐temperature reactor

Tritium management is one of the most critical issues that limit the development of fluoride‐salt‐cooled high‐temperature reactor (FHR); therefore, it is important to figure out the tritium transport characteristics in FHRs. In this paper, 3 works concerning about tritium in FHR are conducted: first, the tritium transport characteristics in the primary loop of FHRs are introduced, including tritium production and speciation, the absorption and desorption by graphite, dissolution and diffusion in molten salt, and permeation through structural materials. Second, the physical and mathematical models are established for tritium transport characteristic analysis in a transportable FHR (TFHR). The tritium transport characteristic analysis code (TAPAS) for TFHR is developed and benchmarked. The results prove the fidelity and accuracy of TAPAS. Finally, the tritium transport characteristics in the TFHR are analyzed systematically by TAPAS. Three conclusions are obtained: (1) tritium in the primary coolant loop is mainly in the form of T₂; (2) when TFHR operates at steady state, the permeation rate of T₂ can be regarded as a constant (9.03 × 10⁹ Bq ? EFPD^?1 ); and (3) ⁷Li enrichment and redox potential of molten salt have great influence on the tritium distribution. This work might provide contribution to the tritium control in FHRs.     

Isotopic and chemical composition of parbati valley geothermal discharges, North-West Himalaya, India

The isotopic compositions of the waters discharged from Parbati Valley geothermal areas indicate a higher altitude meteoric origin, with discharge temperatures reflecting variations in the depth of penetration of the waters to levels heated by the existence of a ‘normal’ geothermal gradient. On the basis of mixing models involving silica, tritium, discharge temperatures and chloride contents, deep equilibration temperatures of 120–140°C were obtained for Manikaran, possibly reaching 160°C at even greater depth. Geothermometers based on sulfate-water ¹⁸O exchange and gas reactions point to similar temperatures. Exceptionally high helium contents of the discharges correspond to apparent crustal residence times of the waters in the order of 10–100 Ma; relative nitrogen-argon contents support a largely meteoric origin of the waters with a possible fossil brine, but no detectable magmatic component.     

Kinetics of deuterium permeation through Zircaloy-4 in the 623–773 K temperature range

Under normal operating conditions in nuclear pressurized water reactors, tritium produced by ternary fission occurring within the uranium fuel may cross the whole cladding in zirconium alloy before being released in primary water during operation, or in containers during transportation and storage. The study aims at identifying and quantifying the rate-limiting steps of this permeation process by using deuterium as isotopic tracer for tritium. A dedicated permeation device revealed that, at 773 K, deuterium permeation kinetics from the metal was limited by the surface recombination reaction. In association with gaseous deuterium charging and Thermal Desorption Spectrometry, the apparent activation energy of the deuterium desorption showed that the permeation device induced stress and strain in the specimens. A stress-free Zircaloy-4 exhibited an apparent activation energy around 240 kJ mol^?1 it dropped down to around 140 ± 10 kJ mol^?1 when under stress, in the 623 K–773 K temperature range.