Isotopic Mixtures Research Articles

Transition between Isotope-Mixing and Nonmixing States in Hydrogen-Deuterium Mixture Plasmas

The transition between isotope-mixing and nonmixing states in hydrogen-deuterium mixture plasmas is observed in the isotope (hydrogen and deuterium) mixture plasma in the Large Helical Device. In the nonmixing state, the isotope density ratio profile is nonuniform when the beam fueling isotope species differs from the recycling isotope species and the profile varies significantly depending on the ratio of the recycling isotope species, although the electron density profile shape is unchanged. The fast transition from nonmixing state to isotope-mixing state (nearly uniform profile of isotope ion density ratio) is observed associated with the change of electron density profile from peaked to hollow profile by the pellet injection near the plasma periphery. The transition from nonmixing to isotope-mixing state strongly correlates with the increase of turbulence measurements and the transition of turbulence state from TEM to ion temperature gradient is predicted by gyrokinetic simulation.

Determination of the Circulation Intensity in a Centrifuge Rotor in the Enrichment of Isotopic Mixtures of Heavy Gases

The circulation flow in a centrifuge during enrichment of isotopic mixtures of heavy gases is determined. Nickel tetraphosphine Ni(PF3)4 was used as the working substance to study the hydraulic and separative characteristics of a centrifuge. The relative circulation parameter m characterizing the efficiency of the multiplication of the primary effect is determined by comparing the computed dependences with the experimental results obtained in this work.

Vacuum-desorption method for separating the H2 + D2 isotope mixture using a quantum ortho–para-conversion process at hydrogen temperature

The effective evacuation and separation (at helium temperature) of a model gas mixture consisting of He, H2, D2, N2, Ar and other components (close to that formed in a thermonuclear reactor) yielding up to 44% of D2 during desorption, is implemented using a newly developed vacuum pump-separator with a non-isothermal multilayer (up to 100 layers) system of working elements (consisting of perforated screening and spacing materials). Improvements to the vacuum-pump separator design and the use of an ortho-para conversion catalyst made it possible to increase the yield of D2 from the model mixture to 64–69% at hydrogen temperature.

Low-temperature separation of helium-helion mixture

Abstract The research is devoted to the problem of designing materials with an adjustable property of permeability. The obtained tool for property regulation allows achieving hyper-selectivity in relation to separation of helium isotope mixtures, as well as some other gas mixtures. The reasearch is theoretical in nature; however, it suggests a clear direction of activity for experimenters. The result obtained is valid for ultrathin barriers of any form. As a result, a new exact solution of the Schrödinger equation of wave dynamics, which is valid for the case of two-barrier systems, is found. This solution allows for comprehensive consideration of the process of wave passage through a barrier and identification of the causes leading to super-permeability of individual components.

Analysis of argon isotope separation by low temperature adsorption

In this work, the estimated calculated values of the critical parameters of argon isotopes 36Ar, 38Ar, 40Ar and the corresponding values of the constants of the Van der Waals, Redlich-Kwong and Peng-Robinson equations of state are obtained. The data obtained make it possible to calculate the adsorption isotherms of argon isotopes on microporous adsorbents. The technique proposed for obtaining analytical expressions for the adsorption isotherms of argon isotopes at cryogenic temperatures makes it possible to estimate the degree of influence of the pressure of the isotope mixture and its composition on the mixture separations coefficients.

Separation of Noble-Gas Isotope Mixtures Using Low-Temperature Adsorption

Separation of noble-gas isotope mixtures by low-temperature adsorption was considered. The proposed conceptual diagram of an experimental pressure-swing adsorption unit included a vacuum-insulated vessel for maintaining cryogenic temperatures, temperature- and pressure-control systems, and vacuum equipment. The directions of applied research performed on the unit were defined. Experimental methodology for studying activated carbon adsorbents and adsorption parameters was proposed. The gasmixture isotopic composition was monitored by mass spectrometry during the adsorption.

Unit cell parameters of 32S8 – 34S8 solid mixtures and their extremal behavior

The behavior of isotopic mixtures of polyatomic molecular compounds can have a critical character. Orthorhombic sulfur α-S8 is a typical representative of polyatomic molecular compounds among simple substances. Samples comprised of orthorhombic sulfur of different 32S and 34S ratio have been prepared and examined with powder X-Ray diffractometry in the temperature region from −100 to +90 °С. Unit cell parameters of sulfur samples with intermolecular isotopic substitution, containing 0.4 to 0.5 parts of 34S8 molecules, differ radically from the samples of the isotopic composition close to pure α-32S8 and α-34S8. Maximal deviation of unit cell volume −0.17% at −100.0 °C is observed for the sample with a part of 34S8 molecules being 0.45. Such a behavior could well be attributed to the ordering between 32S8 and 34S8 molecules in the crystal that can be triggered by lowering temperature.

Advances in Analysis of Microcalorimeter Gamma-Ray Spectra

Microcalorimeters based on transition-edge sensors (TESs) have been successfully deployed in numerous spectroscopic instruments that operate over a large range of incident photon energies. TES microcalorimeter arrays combine unmatched energy resolution with broadband spectral coverage and high quantum efficiency. An important application requiring these characteristics is nondestructive isotopic analysis via gamma-ray spectroscopy of the complex mixtures of actinide isotopes found in the nuclear fuel cycle. Steady progress has been made over the last ten years to develop TES microcalorimeter instruments for this application, leading to arrays that demonstrate significantly better energy resolution than the state-of-the-art high-purity germanium (HPGe) sensors. However, further algorithm development and automation of the data analysis procedure have been required to bring these systems closer to being ready for production use. In this article, we describe recent advances in data analysis techniques for gamma-ray data acquired with microcalorimeter systems. In particular, we discuss new approaches to automated calibration of our spectra, and a new approach for quantifying the uncertainty of peak area estimation for isolated peaks. Our data analysis pipeline has also been automated, requiring minimal manual intervention for full processing of data sets, with performance that is sufficient to allow future deployment of real-time spectrum generation. We show that, using this pipeline, we are able to achieve ~0.25% statistical uncertainty in isotope ratios, which indicates that if systematic errors are controlled, microcalorimeter arrays can achieve better than 1% total uncertainty in these measurements.

Concept of the Fuel Cycle of the IGNITOR Tokamak

In 2015, the development of the conceptual design of IGNITOR, a Russian–Italian experimental thermonuclear tokamak, was completed, and the parameters of all the systems, including the fuel system, were determined. In this work, an integrated design of arrangement of all the tritium-containing gas and secondary water streams expected in the operation of the IGNITOR tokamak was proposed on the basis of analyzing the designs of the fuel cycles of the large thermonuclear facilities JET, TFTR, and ITER. This design includes the storage of deuterium and tritium in a system of gas cylinders at a pressure of 0.4 MPa, the purification of the exhaust gas mixture from the plasma chamber using a “hot getter,” the separation of the deuterium–tritium isotope mixture by displacement gas chromatography, the purification of the process gas and air streams in a wet scrubber, and the detritiation of the water streams by chemical isotope exchange of hydrogen with water. The main technical parameters of equipment in the proposed design were estimated.

Exploiting Dynamic Opening of Apertures in a Partially Fluorinated MOF for Enhancing H2 Desorption Temperature and Isotope Separation.

Deuterium has been recognized as an irreplaceable element in industrial and scientific research. However, hydrogen isotope separation still remains a huge challenge due to the identical physicochemical properties of the isotopes. In this paper, a partially fluorinated metal–organic framework (MOF) with copper, a so-called FMOFCu, was investigated to determine the separation efficiency and capacity of the framework for deuterium extraction from a hydrogen isotope mixture. The unique structure of this porous material consists of a trimodal pore system with large tubular cavities connected through a smaller cavity with bottleneck apertures with a size of 3.6 Å plus a third hidden cavity connected by an even smaller aperture of 2.5 Å. Depending on the temperature, these two apertures show a gate-opening effect and the cavities get successively accessible for hydrogen with increasing temperature. Thermal desorption spectroscopy (TDS) measurements indicate that the locally flexible MOF can separate D2 from anisotope mixture efficiently, with a selectivity of 14 at 25 K and 4 at 77 K.

Kinetics of a Collision-Induced Photon Echo

The nonmonotonic kinetics of a collision-induced photon echo has been investigated for a number of buffer atoms. The collision-induced photon echo was generated at the 174Yb (6s2) 1S0 ↔ (6s6p) 3P1 (0 ↔ 1) transition by a pair of linearly and mutually orthogonally polarized resonant radiation pulses in ytterbium vapor and its mixtures with He, Ne, Ar, Kr, and Xe. The kinetics of the conventional photon echo generated by pulses with identical linear polarizations was recorded in the same mixtures. The derived decay rate constants for both types of echo are equal to within the measurement errors. For the collisions of 174Yb atoms between themselves and with other ytterbium isotopes in a natural mixture of isotopes, an upper limit for the anisotropy parameter has been estimated, 0.22 ± 0.07 of the photon echo signal decay rate.

An inter-comparison of isotopic composition of neon via chemical assays and thermal analyses (IUPAC Technical Report)

Abstract In 2003–2014, a study on the effect of isotopic composition on the triple point temperature of neon was conducted under the framework of a Project involving laboratories from 11 countries. Natural neon from commercial sources of different isotopic composition, high-purity 20Ne and 22Ne isotopes, and certified artificial isotopic mixtures were used. The thermometric studies comprised: a) a total of 131 analytical assays from 3 laboratories on the isotopic composition of samples taken from 31 different bottles of neon with chemical gas purity 99.99 mol % to 99.9995+ mol %, including chemical impurities for some samples, with up to 12 assays per sample; b) multi-laboratory thermal analyses, with accuracies ranging up to better than 50 μK (k≈2), on 39 samples, almost all permanently sealed in metal cells, for the determination of the liquidus-point temperature of the triple point as a function of isotopic composition. The thermometric studies also constitute an international inter-comparison of thermal and analytical assays on the isotopic composition—and occasionally of the chemical impurities—of neon. These tests are critically needed for top-accuracy thermometry. The main results of the inter-comparison of the various chemical assays, and of the comparisons between the assays and the results of thermal analyses, are reported. They show discrepancies in x(20,21,22Ne), especially for x(22Ne), in ‘natural’ neon, for the same gas bottle, equivalent to an uncertainty of up to 165 μK (k = 1) in the triple point temperature, as measured by all testing laboratories, and of about 100 μK (k = 1) as measured from a single testing laboratory. This is an unsatisfactory situation for thermometry, since it is difficult to obtain a reliable and accurate isotopic assay for neon, thus limiting the accuracy of the realisation of the neon triple point temperature as a ITS-90 reference point to well above 50 μK. However, it also discloses a strong limitation in the relevant analytical chemistry.

Control of the hydrogen:deuterium isotope mixture using pellets in JET

Deuterium pellets are injected into an initially pure hydrogen H-mode plasma in order to control the hydrogen:deuterium (H:D) isotope mixture. The pellets are deposited in the outer 20% of the minor radius, similar to that expected in ITER, creating transiently hollow electron density profiles. A H:D isotope mixture of approximately 45%:55% is obtained in the core with a pellet fuelling throughput of similar to previous pellet fuelling experiments in pure deuterium. Evolution of the H:D mix in the core is reproduced using a simple model, although deuterium transport could be higher at the beginning of the pellet train compared with the flat-top phase.

Cascades with Flow Expansion for Simultaneous Concentration of Intermediate Components

A cascade scheme allowing two intermediate-mass isotopes to be concentrated in a single cascade above the maximum admissible concentrations at the outputs of ordinary cascades is proposed. A cascade with two flow expansions and two additional product flows is used for this. For the example of a mixture of tungsten isotopes, it is shown that the concentrations of 183W and 184W can be increased simultaneously up to 70 and 80%, respectively. In addition, additional product flows can be equal to 50–70% of the primary (end) product flow of the cascade.

Разделение многокомпонентной изотопной смеси в процессе заполнения каскада газовых центрифуг

Разделение многокомпонентной изотопной смеси в процессе заполнения каскада газовых центрифуг

Measurements of radial profile of hydrogen and deuterium density in isotope mixture plasmas using bulk charge exchange spectroscopy.

A bulk charge exchange spectroscopy system has been applied to measure the radial profiles of the hydrogen (H) and deuterium (D) density ratio in the isotope mixture plasma in a large helical device. Charge exchange lines of Hα and Dα are fitted by 4 Gaussian of H and D cold components and H and D hot components with 5 parameters by combining the measurement of plasma toroidal rotation velocity with carbon charge exchange spectroscopy. The radial profiles of the relative density of hydrogen and deuterium ions are derived from H and D hot components measured and the beam density calculated from beam attenuation calculation. A proof-of-principle experiment is performed by the H pellet and the D pellet injections into the H-D mixture plasma.

Inversion of the Contribution of an Isotope of Small Relative Concentration to Total Absorption Coefficient of a Mixture of Neon Isotopes Associated with the 3s2–2p4 Transition

Absorption of probe laser radiation by a mixture of even isotopes of neon in a gas discharge plasma is investigated by the method of magnetic scanning of 3s2–2p4 transition. The contours of absorption lines of isotopes are resolved by means of numerical modeling. It is discovered that, upon decrease in relative concentration of one of the isotopes, its contribution to absorption is replaced by gain. The effect is found to be caused by radiative transfer of excitation energy between atoms of different kinds in the absence of a difference in level energies (the process known as optical pumping). The effect of this mechanism turned out to be substantial for the upper level transitions from which to the ground state are allowed while being absent for the lower level of the transition from which such transitions are forbidden although other decay channels are available.

Nonstationary Transfer of Components of an Isotopic Mixture as a Result of the Change in Cascade Flows

A nonstationary process initiated by the change in the values of the flows of light and heavy fractions of a cascade has been modeled using the separation of germanium isotopes as an example. The character of change in the concentration of isotopes in cascade stages and flows as a function of the finite values of the flows has been shown. It has been established that in the course of the nonstationary process, isotopes of intermediate masses can be obtained with a concentration much higher than the maximum attainable values for a three-flow cascade.

Hydrogen Isotope Effects during Water Electrolysis Using Liquid and Polymer Membrane Electrolytes

Hydrogen isotope separation is highly important and equally challenging. Annual production of heavy water (D2O) is over a thousand tons to supply nuclear reactors and for medical and research applications worldwide. Current D2O production methods are expensive due to the low natural abundance of deuterium and high complexity of separation techniques. Demand for low-cost production of heavy water is inevitable with increased usage of nuclear power. Therefore, it is important to develop novel and economically viable methods to concentrate deuterium in water to overcome these demands. The purpose of this project is to study hydrogen isotope effects during the electrolytic decomposition water. Water electrolysis occurs via an oxygen evolution reaction (OER) at the anode and a hydrogen evolution reaction (HER) at the cathode. We have located OER and HER as the two main reactions that can have an isotope effect. Custom-built electrolyzers are used for the water electrolysis experiments where IrO2 is used as the catalyst layer at the anode and Pt on Carbon is used as the catalyst layer at the cathode. Results from using sulfuric acid in H2O and deuterated sulfuric acid in D2O as the liquid electrolytes for water electrolysis in a three-electrode conventional cell will be presented and discussed in the context of hydrogen isotope effects on the OER and HER. A similar comparison is made to study isotope effects at OER and HER in a proton exchange membrane (PEM) cell using Nafion 212 as the solid polymer electrolyte in a custom electrolyzer. Monolayer graphene in its pristine form has been shown to act as a selective barrier allowing proton transmission at rates much higher than deuteron transmission. We have incorporated a graphene layer in between two Nafion membranes to study the effect of graphene on the ability to separate deuterium from a hydrogen/deuterium gas mixture and also from H2O vs D2O electrolysis. Monolayer graphene’s barrier character together with isotope effects of OER and HER of the membrane electrode assembly (MEA) could contribute to a potential low-cost method to separate deuterium from a H/D isotope mixture.

The isotope effect on impurities and bulk ion particle transport in the Large Helical Device

The isotope effect on impurities and bulk ion particle transport is investigated by using the deuterium, hydrogen, and isotope mixture plasma in the Large Helical Device (LHD). A clear isotope effect is observed in the impurity transport but not the bulk ion transport. The isotope effects on impurity transport and ion heat transport are observed as a primary and a secondary effect, respectively, in the plasma with an internal transport barrier (ITB). In the LHD, an ion ITB is always transient because the impurity hole triggered by the increase of ion temperature gradient causes the enhancement of ion heat transport and gradually terminates the ion ITB. The formation of an impurity hole becomes slower in the deuterium (D) plasma than the hydrogen (H) plasma. This primary isotope effect on impurity transport contributes the longer sustainment of the ion ITB state because the low ion thermal diffusivity can be sustained as long as the normalized carbon impurity gradient R/Ln,c, where , is above the critical value (∼−5). Therefore, the longer sustainment of the ITB state in the deuterium plasma is considered to be a secondary isotope effect due to the mitigation of the impurity hole. The radial profile of H and D ion density is measured using bulk charge exchange spectroscopy inside the isotope mixture plasma. The decay time of H ion density after the H-pellet injection and the decay time of D ion density after D-pellet injection are almost identical, which demonstrates that there is no significant isotope effect on ion particle transport.