Behavior Of Hydrogen Isotopes Research Articles

Behavior of Tritium in the Vacuum Vessel of JT-60U

Disassembly of the JT-60U torus was started in 2010 after 18 years D2 operations. In future the vacuum vessel will be treated as non-radioactive ones after the clearance procedure under the Japanese regulation depending on the tritium (T) contamination level. Note that the vessel was manufactured from Inconel 625 steel. Therefore, it was very important to study the hydrogen isotope behavior in Inconel 625 from viewpoint of the clearance procedure. Inconel 625 specimen was exposed to the D2 (92.8 %) – T2 (7.2 %) gas mixture at 573 K for 5 hours. The tritium release from the specimen at 298 K was controlled for about 1 year. After that a part of tritium remaining in the specimen was released by heating up to 1073 K. Other part of tritium trapped in the specimen was measured by chemical etching method. Most of the chemical form of the released tritium was HTO. The contaminated specimen by tritium was released continuously the diffusible tritium under the ambient condition. In the tritium release experiment, the amount of desorbed tritium was about 99% during 1 year. It was considered that the tritium in Inconel 625 was released easily. From these results, the behavior of tritium in the vacuum vessel of the JT-60U torus will be evaluated and discussed

Liquid–solid phase transition of hydrogen and deuterium in silica aerogel

Behavior of hydrogen isotopes confined in disordered low-density nanoporous solids remains essentially unknown. Here, we use relaxation calorimetry to study freezing and melting of H2 and D2 in an ∼85%-porous base-catalyzed silica aerogel. We find that liquid–solid transition temperatures of both isotopes inside the aerogel are depressed. The phase transition takes place over a wide temperature range of ∼4 K and non-trivially depends on the liquid filling fraction, reflecting the broad pore size distribution in the aerogel. Undercooling is observed for both H2 and D2 confined inside the aerogel monolith. Results for H2 and D2 are extrapolated to tritium-containing hydrogens with the quantum law of corresponding states.

Influence of surface morphology and surface area on release behavior of hydrogen isotopes in LiNbO3

Surface processes have profound influence on tritium release behavior in ceramic breeder materials. In this paper, the release behavior of hydrogen isotopes in LiNbO3 is studied by thermal desorption spectroscopy (TDS) with focusing on the influence of the surface morphology and surface area. It is found that the amount of surface hydroxyl groups is proportional to the specific surface area and can be decreased by smoothing the surface roughness through heating pretreatment at high temperatures. The isotope exchange reaction between the surface hydroxyl groups and water molecules residue in the system is discussed and turns out to proceed fast. The release behavior of hydrogen isotopes in LiNbO3 is compared with that in Li2TiO3 studied in our previous work. It reveals that LiNbO3 and Li2TiO3 have similar surface environment and similar concentration of surface hydroxyl groups with the level of 1020m−2. The formation mechanism of hydroxyl groups on the surface is discussed and a model to explain the experimental observations is proposed.

Hydrogen isotope behavior on a water–metal boundary with simultaneous transfer from and to the metal surface

To investigate the behavior of hydrogen on a water–metal boundary, a series of experiments have been performed that studied tritium permeation into a pressurized water jacket through pure iron piping, which contained approximately 1kPa of pure tritium gas at 423K, while monitoring the chemical forms of tritium. Additionally, the behavior of deuterium, which was generated on the heavy water–metal boundary and transferred to the metal, was also investigated using a pressure-proof heavy water vessel. Actual deuterium transfer through various metal piping, such as Fe, Ni, SS304, etc., was detected clearly by QMS at 423–573K. Moreover, using the above heavy water system, we have succeeded in detecting hydrogen isotopes simultaneously transferring from and to the metal surface by introducing hydrogen gas to the Ni piping after deuterium permeation from the heavy water side had stabilized.

Modeling hydrogen isotope behavior in fusion plasma-facing components

In this work, we focus on understanding hydrogen isotope retention in plasma-facing materials in fusion devices. Three common simulation methods are usually used to study this problem that includes Monte Carlo, molecular dynamics, and numerical/analytical methods. A system of partial differential equations describing deuterium behavior in tungsten under various conditions is solved numerically to explain recent data compared to other methods. The developed model of hydrogen retention in metals includes classic, intercrystalline and trapped-induced Gorsky effects. The bombardment and depth profile of 200eV deuterium in single crystal tungsten are simulated and compared with recent work. The total deuterium retention at various temperatures and fluences are also calculated and compared with available data. The results are in reasonable agreement with data and therefore, this model can be used to estimate deuterium inventory and recovery in future fusion devices.

Hydrogen isotope exchange in proton-conducting oxides during proton and deuteron irradiation

It has been found that during accelerator beam deuteron irradiation of a proton-conducting oxide containing protium H/D isotope exchange between beam ions and dissolved ions takes place. This isotope exchange was also observed during high-energy proton irradiation of the oxide containing dissolved deuterium atoms. These results provide evidence to a new type of hydrogen isotope exchange. Any appreciable effects of conjugate diffusion of hydrogen and oxygen ions and of the interface processes on the isotope exchange rate were eliminated. In this type of exchange the rate of replacement of H+ by D+ and of D+ by H+ was determined only by the properties of the crystal. The discovered effect was used in our study to obtain experimental data characterizing the dynamic and equilibrium behavior of hydrogen isotopes in the oxide BaZr0.9Y0.1O3 − δ.

Separation Factors for Hydrogen Isotopes in Palladium Hydride

This investigation examines how equilibrium pressures of single isotope metal–hydrogen systems can be used to determine the separation behavior of hydrogen isotopes in a mixed-isotope metal hydrogen system. The separation factor for a hydrogen–deuterium system, αHD, describes the equilibrium hydrogen isotope partition between the solid and gaseous phases. Very few values of αHD are reported for metals other than palladium, and the values for Pd are scattered with the origin of the scatter not fully understood. Wicke and Nernst and Trentin et al. have proposed models that relate αHD to the ratio of single isotope equilibrium pressures and the isotopic composition of the solid. The approaches of these models and the resulting equations appear to differ; however, as will be shown here, they are identical. It also will be shown that Raoult’s law, employed by both models, is not needed. This puts the model derivation on a firmer theoretical basis. New measurements of αHD values are determined over a large temperature range and D/H ratio in β-phase Pd hydride, and they are compared with the model predictions, validating the model. Since experimental values for αHD are often not available for other systems, while single isotope equilibrium pressures are available, the model provides a valuable tool for predicting separation factors. Moreover, the model can also be used to estimate separation factors involving the third hydrogen isotope, tritium.

Specific equilibrium behavior of hydrogen isotopes adsorbed onto synthetic zeolite A-type governed by lithium cations

Since synthetic zeolites (SZs) are powerfully adsorptive for hydrogen isotopes at cryogenic temperatures such as liquefied nitrogen, adsorption processes using these have been considered applicable to such as recovery of tritium from the lithium blanket of DT fusion reactor system. Onto these zeolites the adsorptions isotherms for hydrogen isotopes onto SZ-NaA, SZ-CaA and SZ-NaX at 77.4K were already clarified experimentally and analytically. These isotherms exhibit similar profiles of Langmuir type. In this work, adsorption isotherms were examined for H2 and D2 on SZ-LiA at 77.4K. SZ-LiA was made from SZ-NaA by exchanging its sodium ions for lithium ones, provided by TOSOH Corp. The experimental results demonstrate the specific equilibrium behavior of hydrogen isotopes adsorbed on SZ-LiA, deviating from isothermal profiles on SZ-CaA and SZ-NaX. SZ-LiA show the isothermal profiles of adsorption for H2 and D2 similar to on the conventional zeolites in the range from around 1kPa to the atmospheric pressure, but exhibit a plateau around 1mol/kg between 0.1Pa and 100Pa, while other zeolites show linearly profiling isotherms. This deviation indicates the adsorptive power of SZ-LiA remarkably greater than that of the others.

Formation of lithium-tritide by hot atom reactions of tritium produced in Pb-16Li

The release behaviors of hydrogen isotopes in Pb-16Li introduced by thermal gas exposure or produced by thermal neutron irradiation were compared to investigate hot atom reactions of tritium. The solubility of hydrogen isotope was evaluated to be S=6.56×10−7 exp(−0.11 [eV]/kT) [at. fr, Pa0.5], which is consistent with the literature values. The tritium TDS spectra for Pb-16Li with thermal neutron irradiation showed that about 5% of tritium was released at single release stage around 600K, which was higher than the melting point of Pb-16Li, although no release peak was found at around 600K for the hydrogen isotope-doped Pb-16Li. The kinetic analysis indicated that the tritium release would be associated with the dissociation of Li-T bond, indicating that LiT was formed in Pb-16Li by thermal neutron irradiation, suggesting that the formation of Li-T bonds should be considered to estimate tritium retention in Pb-16Li eutectic blanket systems in fusion reactors.

Release behavior of hydrogen isotopes thermally sorbed in Li2TiO3 single crystal

Understanding of fundamental processes governing tritium release in tritium breeder materials is important for blanket design in fusion reactors. In this paper, the release behavior of hydrogen isotopes in Li2TiO3 single crystal samples with different sizes was studied by thermal desorption spectroscopy (TDS). It was indicated that with the size of single crystal samples decreasing to several μm, the rate-controlling step in the release of hydrogen isotopes moves from bulk diffusion to surface processes. Regarding the amount of hydroxyl groups, the surface hydroxyl groups became predominant for the grains smaller than several tens of μms. The amount of surface hydroxyl groups was influenced by the specific surface area and surface conditions.

Diffusion behaviors of hydrogen isotopes in niobium from first-principles

We investigate diffusion behaviors of hydrogen (H), deuterium (D), and tritium (T) in bulk niobium (Nb) using first-principles method. The diffusion energy barrier with quantum-correction has been calculated to be 0.12 eV, which is in good agreement with the experimental value of ∼0.106 eV. According to diffusion theory presented by Wert and Zener, the diffusion pre-exponential factors of H, D, and T are shown to be 7.74×10−8 m2 s−1, 5.47×10−8 m2 s−1 and 4.48×10−8 m2 s−1, respectively. These results are also in quantitative agreement with the corresponding experimental values.

Study on the retention behavior of hydrogen isotopes and the change of chemical states of boron film exposed to hydrogen plasma in LHD

The behavior of hydrogen retention and the change of chemical states of boron film exposed to hydrogen plasma in LHD were investigated. The sample was prepared in LHD, and atomic concentrations for the boron film after hydrogen plasma exposure were changed from 75% for boron, 15% for carbon and 8% for oxygen to 53%, 18% and 22%, respectively. BC bond was a major chemical state of the boron film after hydrogen plasma exposure, although abundance of BB bond was the highest before the plasma exposure. Total hydrogen retention measured by TDS was evaluated to be 1.7×1020Hm−2, and the retentions of hydrogen as BHB, BH and BCH bonds were, respectively, 4.8×1019, 7.2×1019 and 5.2×1019Hm−2. It was concluded that the hydrogen retention could be estimated by taking account not only of chemical states of impurities, but also of hydrogen depth profile.

Overview of the US–Japan collaborative investigation on hydrogen isotope retention in neutron-irradiated and ion-damaged tungsten

The effect of neutron-irradiation damage has been mainly simulated using high-energy ion bombardment. A recent MIT report (PSFC/RR-10-4, An assessment of the current data affecting tritium retention and its use to project towards T retention in ITER, Lipschultz et al., 2010) summarizes the observations from high-energy ion bombardment studies and illustrates the saturation trend in deuterium concentration due to damage from ion irradiation in tungsten and molybdenum above 1 displacement per atom (dpa). While this prior database of results is quite valuable for understanding the behavior of hydrogen isotopes in plasma facing components (PFCs), it does not encompass the full range of effects that must be considered in a practical fusion environment due to short penetration depth, damage gradient, high damage rate, and high primary knock-on atom (PKA) energy spectrum of the ion bombardment. In addition, neutrons change the elemental composition via transmutations, and create a high radiation environment inside PFCs, which influences the behavior of hydrogen isotope in PFCs, suggesting the utilization of fission reactors is necessary for neutron-irradiation. Under the framework of the US–Japan TITAN program, tungsten samples (99.99at.% purity from A.L.M.T. Co.) were irradiated by fission neutrons in the High Flux Isotope Reactor (HFIR), Oak Ridge National Laboratory (ORNL), at 50 and 300°C to 0.025, 0.3, and 2.4dpa, and the investigation of deuterium retention in neutron-irradiated tungsten was performed in the Tritium Plasma Experiment (TPE), the unique high-flux linear plasma facility that can handle tritium, beryllium and activated materials. This paper reports the recent results from the comparison of ion-damaged tungsten via various ion species (2.8MeV Fe2+, 20MeV W2+, and 700keV H−) with that from neutron-irradiated tungsten to identify the similarities and differences among them.

Sorption and desorption behavior of hydrogen isotopes from tungsten deposits caused by deuterium gas or deuterium plasma exposure

To understand the behavior of hydrogen isotopes in deposits formed on plasma-facing wall is an important issue for development of a fusion reactor. In this study, sorption/desorption behaviors of hydrogen isotopes when tungsten deposits were exposed to deuterium gas or deuterium plasma at 300°C were investigated. Samples of tungsten deposits were produced by the sputtering method using hydrogen plasma. After deuterium gas exposure or deuterium plasma exposure, the desorption behavior of hydrogen isotopes from the deposit was observed by the thermal desorption spectroscopy method. It was found that not a small amount of deuterium is retained in tungsten deposit by not only the plasma exposure but also the gas exposure while the amount of hydrogen incorporated in the deposit during sputter-deposition process is reduced. The amount of deuterium retained in the deposit by the plasma exposure was larger than that by the gas exposure in the experimental conditions in this work. The amount of hydrogen left after deuterium plasma exposure was larger than that after deuterium gas exposure.

First-principles investigation on diffusion and permeation behaviors of hydrogen isotopes in molybdenum

We have investigated diffusion and permeation behaviors of hydrogen (H), deuterium (D), and tritium (T) in bulk molybdenum (Mo) by a first-principles calculations combined with simplified models. The H diffusion energy barrier with quantum correction is shown to be 0.12 eV, in good agreement with the value of 0.11 eV obtained from experiment. According to the diffusion theory presented by Wert and Zener, the diffusion coefficients of H, D and T are estimated, respectively. The H diffusion coefficient is found to be D = 1.27 × 10 - 7 exp ( - 0.12 eV / kT ) m 2 s - 1 , which is also basically consistent with the experiment. Permeability Φ can be approximately evaluated in terms of Φ = SD, where S and D are the solubility and the H diffusion coefficient, respectively. We found that H has the low solubility in bulk Mo, consistent with the results at the temperature from 900 K to 1500 K in the earlier experiment. The permeability of H isotopes are calculated to be one order of magnitude larger than those of the experimental values. Such discrepancy should stem from that the “defect-free” Mo in the present calculations is considered. The permeation flux of H isotopes are finally examined. At the temperature of 1200 K, the fluxes of H, D, and T are calculated to be 1.27 × 10 −6 mol m −2 s −1, 8.95 × 10 −7 mol m −2 s −1, and 7.30 × 10 −7 mol m −2 s −1, respectively.

Deuterium retention in Fe2O3 under low-energy deuterium-plasma exposure

Stainless steel (SUS) is used as the structure material in nuclear fusion devices. Heating and O2 plasma discharge are considered for the removal of tritium. Oxide layer growth is anticipated on heating SUS at a high temperature in low-pressure residual O2 gas. When O2 plasma discharge is performed, oxygen plasma reaches the structure material and iron oxides such as Fe2O3 are formed. Thus, a knowledge of the retention behavior of hydrogen isotopes or deuterium (D) in the oxide layers is important in designing the devices. We investigated D retention in Fe2O3 films and the influence of Fe2O3 crystal structure on D retention and found that D retention in γ-Fe2O3 (cubic-maghemite) is larger than that in α-Fe2O3 (hexagonal-hematite). The results for Fe2O3 are compared with those for SUS and Fe.

Gas chromatographic separation of hydrogen isotopes on columns packed with alumina, modified alumina and sol–gel alumina

The stationary phase of alumina adsorbents, prepared by different chemical processes, was used to study the separation behaviour of hydrogen isotopes. Three types of alumina, obtained by conventional hydroxide route alumina coated with silicon oxide and alumina prepared by internal gelation process (IGP), were used as packing material to study the separation of HT and T(2) in a mixture at various temperatures. The conventional alumina and silicon oxide coated alumina resolved HT and T(2) at 77K temperature with different retention times. The retention times on SiO(2) coated columns were found to be higher than those of other adsorbents. However, the column filled with IGP alumina was found to be ideal for the separation of HT and T(2) at 240 K. The peaks were well resolved in less than 5 min on this column.

Development of Monte Carlo Simulation Code to Model Behavior of Hydrogen Isotopes Loaded into Tungsten Containing Vacancies

The behavior of hydrogen isotopes implanted into tungsten containing vacancies was simulated using a Monte Carlo technique. The correlations between the distribution of implanted deuterium and fluence, trap density and trap distribution were evaluated. Throughout the present study, qualitatively understandable results were obtained. In order to improve the precision of the model and obtain quantitatively reliable results, it is necessary to deal with the following subjects: (1) how to balance long-time irradiation processes with a rapid diffusion process, (2) how to prevent unrealistic accumulation of hydrogen, and (3) how to model the release of hydrogen forcibly loaded into a region where hydrogen densely exist already.

Successive Hydrogen Isotope Separation/Enrichment by Pressure Swing Adsorption Using SZ-13X Column

Focusing on the behavior of hydrogen isotopes onto synthetic zeolites (SZ) at cryogenic temperatures such as liquefied nitrogen, we have been developing a system of pressure swing adsorption (PSA) process for hydrogen isotope separation applicable to fusion fuel processing, environmental tritium safety confinement or recovery of tritium from heavy water reactors. We have previously reported the experimental results of successive isotope separation and enrichment in a H2-D2 mixture by the PSA process using a single column packed with SZ-5A. In this work, a PSA experiment using SZ-13X was carried out in a similar way to the previous experiment for comparing the functional adsorbents. The result shows that the PSA process operation with SZ-13X can make the performance of heavier isotope enrichment with efficiency at a factor of near twice in comparison to the same operation with SZ-5A.

Conductance Characteristics of Hydrogen Isotopes between Viscous and Molecular Flow Regions in Spherical Pellet Packed-Beds at 77.4 K

We have been studying the dynamic behavior of hydrogen isotopes flowing between viscous and molecular regions in an adsorbent packed-bed column, for the purpose of developing a pressure swing adsorption (PSA) process system for hydrogen isotope separation. This PSA system consists of adsorption, evacuating desorption and hydrogen replenishing processes. The kinetics in the adsorption process has been becoming to be predictable in theoretical simulation based on experimental results, but it is difficult as yet to simulate the dynamic behaviors in evaluating and replenishing processes because of the complicated geometry of passages in a packed-bed and the change of gas flow patterns between viscous and molecular regions depending on not only the pressure but also the dimension of passages. In the dynamics, the important factor should be known is the mass flow conductance in pellet packed-bed. In this work, we carried out the experiment for examining the dependence of the conductance on the diameter of particles packed in a column, since the geometrical and dimensional conditions of passages are affected by the size of packing pellets. From the experimental result and its analysis, we clarified the pressure and particle-size dependences of the conductance of hydrogen isotopes in spherical pellet packed-beds.