수소 동위 원소는 중성자 수에 따라 경수소, 중수소, 삼중수소로 분류될 수 있으며, 각 원소는 특정 분야에서 사용 되고 있다. 구체적으로, 중수소는 전자 산업, 원자력에너지 산업, 분석기술 산업, 의약품 산업, 그리고 통신 산업에서 관심을 받고 있다. 냉각 증류, 열 주기 흡수 공정, Girdler sulfide 공정, 그리고 수전해와 같은 기존의 방법들은 각각의 장단점을 가지 고 있지만, 공통적으로 막대한 에너지를 필요로 하는 공정에 기반한다는 문제점을 가지고 있다. 높은 에너지 효율을 보이는 기술을 기반으로 분리하는 공정의 개발이 요구되는 실정이다. 이런 맥락에서 막을 사용한 수소 동위 원소 분리 기술이 에너 지 소비를 줄이는 유망한 해결책 중 하나라 볼 수 있다. 이 총설에서는 분리막을 활용한 수소 동위원소 분리에 관한 선행 연 구와 그들의 작동 원리를 소개하고자 한다. 특히 최근 제시되고 있는, 그래핀 기반 전기적 펌핑을 통한 수소 동위원소 분리 기술에 대하여 다루고자 한다. 분리막을 활용한 수소 동위원소 분리에 대한 기술은 이제 개념이 제안되기 시작한 단계이며, 많은 부분에서 해결해야 할 난제가 있다. 그러나 이를 달성할 경우 경제적인 효과가 상당할 것으로 판단된다. 이를 위한 향후 연구 방향에 대해서 논하고자 한다.

Tritium is radioactive isotope, emitting beta ray, released as tritiated water from nuclear power plants. Due to the danger of radioactive isotope, the appropriate separation of tritium is essentially carried out for environment and safety. Further, it is also promising material for energy production and research. The tritiated water can be treated by diverse techniques such as water distillation, cryogenic distillation, Girdler-sulfide process, and catalytic exchange. After treatment, it is more desirable to convert as gas phase for storage, comparing to liquid phase. However, achieving complete separation of hydrogen gases with very similar physical and chemical properties is significantly challenging. Thus, it is necessary to develop materials with effective separation properties in gas separation. In this presentation, we present hydrogen isotope separation in the gas phase using modified mesoporous silica. Mesoporous silica is a form of silica that is characterized by its mesoporous structure possessing pores that range from 2 to 50 nm in diameter. This material can be functionalized to selectively capture and separate molecules having specific size and affinity. Here, the silver and copper incorporated mesoporous silica was synthesized to tailor a chemical affinity quantum sieving effect, thereby providing separation efficiency in D2/H2. The adsorption quantities of H2 and D2 were determined by sorption study, and the textural properties of each mesoporous silica were analyzed using N2 physisorption. The selectivity (D2/H2) in diverse feed composition (1:1, 1:9, and 1:99 of D2/H2) was estimated by applying ideal adsorbed solution theory to predict the loading of the gas mixture on bare, Ag- and Cu-mesoporous silica based on their sorption study. Further, the performance of each mesoporous silica was evaluated in the breakthrough adsorption under 1:1 mixture of D2 and H2 at 77 K.

Pt/C catalysts were prepared using black carbon (CB), and evaluated for their potential application as a catalyst of liquid-phase catalystic exchange for tritium treatment. CB was treated with 10% H2O2 solution for 0 and 2 hours at 105°C, Ethylene glycol and 40wt% Pt were added to the dried treated sample to prepare a Pt/C catalyst. The physical and chemical properties of the prepared catalysts were evaluated by BET, XRD, elemental analysis (EA), and TEM analyses. As a result of BET analysis, the surface area of CB without 10% H2O2 was 237.2 m2·g-1, and after treatment with 10% H2O2, it decreased to 181.2 m2·g-1 for 2 hours. However, the internal surface area increased, indicating the possibility that more Pt could be distributed inside the CB treated with 10% H2O2. In the XRD analysis results, the presence of Pt was confirmed by observing the Pt peak in the prepared Pt/C catalyst, and it was also observed through TEM analysis that Pt was evenly distributed within the CB. The elemental analysis (EA) results showed that the ratio of S and N decreased and the ratio of O increased with increasing 10% H2O2 treatment time. The H2O2 treated carbon supported Pt catalysts and polytetrafluoroethylene were then loaded together on a foamed nickel carrier to obtain hydrophobic catalysts. Our hydrophobic Pt catalyst using H2O2 treated black carbon are expected to be usefully used in the tritium treatment system.

Hydrogen isotope separation involves the separation of hydrogen, deuterium, tritium, and their isotopologues. It is an essential technology for removing radioactive tritium contamination and for obtaining valuable hydrogen isotope resources. Among various hydrogen isotope separation technologies, water electrolysis technology exhibits a high separation factor. Consequently, the electrolysis of tritiated water is of paramount importance as a tritium enrichment method for treating tritium-contaminated water and for analyzing tritium in environmental samples. More recently, hydroelectrolysis technology, which utilizes proton exchange membranes (PEM) to reduce water inventory, has gained favor over traditional alkaline hydroelectrolysis. Nevertheless, it is crucial to decrease the hydrogen permeability of the PEM in order to mitigate the explosion risk associated with tritium hydrogen electrolysis devices. Additionally, efforts are needed to enhance the hydrogen isotope selectivity of the PEM and optimize the manufacturing process of the membrane-electrode assembly (MEA), thereby improving both hydrogen isotope separation performance and water electrolysis efficiency. In this presentation, we will delve into two key aspects. Firstly, we’ll explore the reduction of hydrogen permeability and the enhancement of the hydrogen isotope separation factor in PEM through the incorporation of 2D nanomaterial additives. Secondly, we’ll examine the influence of various MEAs preparation methods on electrolysis and isotope separation performances. Lastly, we will discuss the effectiveness of the developed system in separating deuterium and tritium.

The development of separation method of radioactive tritium is imperative for treating tritiumcontaminated water originating from nuclear facilities. Polymer electrolyte membrane electrolysis technology represents a promising alternative to conventional alkaline electrolysis for tritium enrichment. Nevertheless, there has been limited research conducted thus far on the composition of membrane electrode assemblies (MEAs) specifically optimized for tritium separation, as well as the methods used for their fabrication. In this study, we conducted an investigation aimed at optimizing MEAs specifically tailored for tritium separation. Our approach involved the systematic variation of MEA components, including the anode, cathode, porous transport layer, and electrode formation method. The water electrolysis efficiency and the H/D separation factor in deuterated water (1%) were evaluated with respect to both the preparation method and the composition of the MEA. To assess the long-term stability of the MEAs, changes in cell voltage, resistance, and the active electrode area were analyzed using impedance analysis and cyclic voltammetry. Furthermore, we examined H/D separation factor both before and after degradation. The results showed that MEAs with different anode/cathode configurations and electrode formation methods improved the electrolysis efficiency compared to commercial MEAs. In addition, the degree of change in the resistance value was also different depending on the electrode formation method, indicating that the electrode formation method has a significant impact on the stability of the electrolysis system. Therefore, the study showed that the efficiency and long-term stability of the water electrolzer can be improved by optimizing the MEA fabrication method.

Heavy water (D2O) is a coolant as well as a moderator of pressurized heavy water reactors (PHWRs). During operation of PHWRs, deuterium (H-2, D) in heavy water is gradually converted to tritium (H-3, T), which is a radioactive nuclide with a half-life of 12.3 years, by capturing neutron. Various radioactive wastes contaminated by T are generated upon the PHWR operation. Owing to the similarity of D and T, they behave together a form of water (either liquid or vapor) in a normal circumstance. To handle D and T with the water form is quite difficult because it is not a solid and is highly mobile in nature. In this study, a mineralization technique to fix D and T in a solid form is suggested. It is considered that hydroxide minerals, which have low solubility in water, might tightly bind D and T in non-mobile, solid-state media. Feasibility of this strategy is studied by using a copper-based hydroxide mineral, atacamite. Atacamite is a natural mineral found in copper deposits with chemical formula of Cu2Cl(OH)3. Atacamite can be simply synthesized in laboratories by a precipitation method using copper chloride and calcium carbonate as precursors. Both chemicals were added into heavy water to obtain pale-green precipitates. Heavy water is the only source for D in this reaction and thus deuterated mineral is expected to be form. The obtained deuterated mineral, suspected to be Cu2Cl(OD)3, was then immersed in natural deionized water (extremely low D2O concentration) for several days to identify how fast D in Cu2Cl(OD)3 dissolves into water. In a preliminary Fourier transform infrared (FTIR) spectroscopy, absorption peaks related to HDO and D2O were not observed in the deionized water which is recovered after the immersion test, suggesting that D remained stable in the synthesized mineral. However, owing to low detection limit of FTIR, more precise analysis should be taken to clearly identify the stability of D of the deuterated atacamite. If deuterated hydroxide minerals are found to have sufficiently high D stability in natural water, they can be further treated with cement or other stabilization media to form a final wasteform for underground disposal.

For decontamination and quantification of trace amount of tritium in water, an efficient separation technology capable of enriching tritium in water is required. Electrolysis is a key technology for tritium enichment as it has a high H/T and D/T separation factors. To separate tritium, it is important to develop a proton exchange membrane (PEM) electrolyzer having high hydrogen isotope separation factor as well as high electrolyzer cell efficiency. However, there has not been sufficient research on the separation factor and cell efficiency according to the composition and manufacturing method of the membrane electrode assembly (MEA) Therefore, it is necessary to study the optimal composition and manufacturing method of the MEA in PEM electrolyzer. In this study, the H/D separation factor and water electrolysis cell efficiency of PEM electrolyzer were analyzed by changing the anode and cathode materials and electrode deposition method of the MEA. After the water electrolysis experiment using deionized water, the D/H ratio in water and hydrogen gas was measured using a cavity ring down spectrometer and a mass spectrometer, respectively, and the separation factor was calculated. To calculate the cell efficiency of water electrolysis, a polarization curves were obtained by measuring the voltage changes while increasing the current density. As a result of the study, the water electrolyzer cell efficiency of the MEA fabricated with different anode/cathode configurations and electrode formation methods was higher than that of commercial MEA. On the other hand, the difference in H/D separation factor was not significant depending on the MEA fabrication methods. Therefore, using a cell with high cell efficiency when the separation factor is the same will help construct a more efficient water electrolysis system by lowering the voltage required for water electrolysis.

Hydrogen isotopes (H, D, T) separation technologies have received great interest for treatments of tritiated liquid waste produced in Fukushima. In addition, the separated deuterium and tritium can be utilized in various industries such as semiconductors and nuclear fusion as expensive and rare resources. However, separating hydrogen isotopes in gas and liquid forms still requires energyintensive processes. To improve efficiency and performance of hydrogen isotope separation, we are developing water electrolysis, cryosorption, distillation, isotope exchange, and hydrophobic catalyst technologies. Furthermore, an analytical method is studied to evaluate the separation of hydrogen isotopes. This presentation introduces the current status of hydrogen isotope research in this research group.

Deuterium is a crucial clean energy source required for nuclear fusion and is a future resource needed in various industries and scientific fields. However, it is not easy to enrich deuterium because the proportion of deuterium in the hydrogen mixture is scarce, at approximately 0.016%. Furthermore, the physical and chemical properties of the hydrogen mixture and deuterium are very similar. Therefore, the efficient separation of deuterium from hydrogen mixtures is often a significant challenge when using modern separation technologies. Recently, to effectively separate deuterium, studies utilizing the ‘Kinetic Quantum Sieving Effect (KQS)’ of porous materials are increasing. Therefore, in this review, two different strategies have been discussed for improving KQS efficiency for hydrogen isotope separation performance using nanoporous materials. One is the gating effect, which precisely controls the aperture locally by adjusting the temperature and pressure. The second is the breathing phenomenon, utilizing the volume change of the structure from closed system to open system. It has been reported that efficient hydrogen isotope separation is possible using these two methods, and each of these effects is described in detail in this review. In addition, a specific-isotope responsive system (e.g., 2nd breathing effect in MIL-53) has recently been discovered and is described here as well.

Hydrogen isotopes (i.e. deuterium and tritium) are supplied to the tokamak in the International Thermonuclear Experimental Reactor (ITER) fuel cycle. One important part of the ITER fuel cycle is the recycling of unused fuel back to the tokamak, as almost 99 % of fuel is unburned during fusion reaction. For this, cryogenic distillation has been used in the isotope separation system (ISS) of ITER, but this technique tends to be energy-intensive and to have low selectivity (typically below 1.5 at 24 K). Recently, efficient isotope separation by porous materials has been reported in the so-called quantum sieving process. Hence, in this study, hydrogen isotope adsorption behavior is studied using chemically stable ZIF-11. At low temperature (40 K ~ 70 K), the adsorption increases and the sorption hysteresis becomes stronger as the temperature increases to 70K. Molar ratio of deuterium to hydrogen based on the isotherms shows the highest (max. 14) ratio at 50 K, confirming the possibility of use as a potential isotope separation material.

The gas adsorption isotherm requires accurate measurement for the analysis of porous materials and is used as an index of surface area, pore distribution, and adsorption amount of gas. Basically, adsorption isotherms of porous materials are measured conventionally at 77K and 87K using liquid nitrogen and liquid argon. The cold volume calibration in this conventional method is done simply by splitting a sample cell into two zones (cold and warm volumes) by controlling the level sensor in a Dewar filled with liquid nitrogen or argon. As a result, BET measurement for textural properties is mainly limited to liquefied gases (i.e. N2 or Ar) at atmospheric pressure. In order to independently investigate other gases (e.g. hydrogen isotopes) at cryogenic temperature, a novel temperature control system in the sample cell is required, and consequently cold volume calibration at various temperatures becomes more important. In this study, a cryocooler system is installed in a commercially available BET device to control the sample cell temperature, and the automated cold volume calibration method of temperature variation is introduced. This developed calibration method presents a reliable and reproducible method of cryogenic measurement for hydrogen isotope separation in porous materials, and also provides large flexibility for evaluating various other gases at various temperature.