Desorption Of Hydrogen Isotopes Research Articles

The engineering sizing of the packed desorption column of hydrogen isotopes from Pb–17Li eutectic alloy. A rate based model using experimental mass transfer coefficients from a Melodie loop

The model of the desorption of hydrogen isotopes from lead lithium alloy in a packed column is derived from the first principles using the plug flow in the liquid phase either the plug flow or ideal mixing in the gas phases. Sievert's law of non-linear equilibrium is followed. The volumetric mass transfer coefficient kLa and its dependence on the liquid metal flow rate are evaluated on the basis of the Melodie loop experiments.The presented model is used for evaluation of the minimum flow rate of the purge gas for which the concentration of the isotope in the gas leaving the column is at its highest, while the driving force of the interfacial transport of the isotope is still not reduced and the tritium desorption efficiency is therefore retained. The potential effect of the axial dispersion in the gas and liquid phase is evaluated. Highlighted are the issues of the optimum packing geometric surface area, above which the efficiency starts to decrease, and of the role of the surface tension and the contact angle with regard to the wettability of the packing. On the basis of the findings related to these factors, the Mellapak 500Y and Mellapak packings with flat surfaces are recommended for the tests aiming to intensify the tritium desorption efficiency in the packed columns. The models were used for the engineering sizing of the packed columns in two breeding blanket concepts for the DEMO plant – utilizing DCLL (dual coolant lead lithium) and HCLL (helium cooled lithium lead).

A First Simulation Study of Hydrogen Isotope Accumulation and Diffusion in Tungsten First Wall of HiPER Inertial Fusion Facility

The study of the retention and desorption of hydrogen isotopes and helium atoms in first-wall materials is key for the design of future fusion reactors, not only for the effect of the materials on the degradation of the wall properties but also for the implications in tritium management strategies.A diffusion model of the implanted H, D, T, and He species in a 1-mm-thick first wall of tungsten for the two initial phases of the proposed European laser fusion project HiPER (namely, phases 4a and 4b) has been implemented using the tritium migration analysis program TMAP7. The effects of the abrupt temperature increases, working temperatures, and the operational pulsing modes on the diffusion are studied. Although a detailed treatment of the different trapping mechanisms has been omitted, meaningful quantitative results on the accumulation, desorption, and time intervals to reach a stationary state are presented and discussed.

Radiation enhanced deuterium absorption for Al2O3 and macor ceramic

Absorption, diffusion, and desorption of hydrogen isotopes are expected to occur during operation in future fusion reactors and these processes will strongly depend on the irradiation conditions, neutron flux and purely ionizing radiation. The main aim of the work is to address the ionizing radiation induced absorption of hydrogen isotopes in Al2O3. Thermo stimulated desorption (TSD) measurements were carried out for both electron irradiated and unirradiated samples in order to evaluate the possible radiation enhanced retention of the previously loaded deuterium. Deuterium enhanced absorption and stabilization have been observed. TSD measurements indicate that the temperature for desorption release of the previously absorbed deuterium increases due to the ionizing radiation.

Retention and Desorption Behaviors of Hydrogen Isotopes in Gamma-Ray Irradiated Li2TiO3

Annihilation behaviors of irradiation defect and, correlation of these behaviors with deuterium trapping and desorption in gamma-ray irradiated Li2TiO3, which is one of the candidates for tritium breeding material, were studied by means of an ESR(Electron Spin Resonance) method and TDS (Thermal Desorption Spectroscopy). From the ESR spectra, gamma-ray irradiation induced irradiation defects such as E’-centers, oxygen-hole centers which were expected to be tritium trapping sites. These irradiation defects were annihilated in the temperature range of 500-650 K. From the TDS spectra for Li2TiO3 exposed to D2 gas, the deuterium desorption behavior was found to consist of four stages, corresponding retention as the surface, in E’-center and as hydroxides bound with Ti or Li. In addition, most of deuterium was released as water form around 400, 550 and 650K. By comparison of the amounts of the deuterium retentions with or without the gamma-ray irradiation, the retention of deuterium trapped with the irradiation defects was increased by gamma-ray irradiation, indicating that the irradiation defects like E’-centers induced by gamma-ray irradiation would be one of the tritium trapping sites in tritium breeding materials. The activation energy of hydrogen isotope desorption from the E’-center was estimated to be 0.63 eV for gamma-ray irradiated Li2TiO3, showing good agreement with that of the recombination reaction between the E’-center and the oxygen-hole center. These results indicated that the tritium desorption was governed by the annihilation of the E’-centers.

Ionizing radiation-stimulated diffusion and desorption of hydrogen from metals

The processes of hydrogen diffusion from a sample depth activated by electrons with an energy of tens of keV are studied. The difference from the known models of electron-stimulated desorption, which consider as a rule electron energies from 0.5 to several keV, is noted. The proposed model is shown to correspond to at least two established experimental facts: the nonlinear dependence of hydrogen isotope desorption on the electron beam current density affecting the sample and the dependence of hydrogen desorption on the irradiation time of the sample.

Numerical simulation of hydrogen desorption from thin metallic films

Metal–hydrogen systems are of great basic and technological interest. In fusion reactors, absorption and desorption of hydrogen isotopes by the first wall and blanket structure are open problems. Hydrogen accumulation at radiation-induced defects in steel may have serious detrimental effects on the structure of steel. In this work, we present the results of a numerical code realized for simulating the hydrogen desorption processes and point out the advantage related with the numerical approaches to the problem. Indeed, as opposed to the analytical procedures which need approximations to avoid mathematical complications to include traps coverage, the numerical approaches work without any approximation.

Hydrogen Isotope Behavior in Type 316 Stainless Steel Sorbed by Various Methods

Typical materials for components, type 316 stainless steel (316-SS), were chosen as a sample and hydrogen isotope was charged by various methods, water adsorption, electrolysis and ion irradiation to elucidate hydrogen isotope behavior on/in SS. The chemical states of SS surface were studied by XPS and the hydrogen isotope retention and its desorption behavior were analyzed by TDS. Two types of surface finish, namely non-pretreated sample and pretreated sample by polish and annealing were prepared. It was found that the oxy-hydroxide and hydroxide were formed on the surface layer. The hydrogen isotope desorption stages consisted of three stages, namely the desorption stages from oxy-hydroxide, hydroxide and bulk hydrogen. A large amount of deuterium was trapped by the oxy-hydroxide layer for the non-pretreated sample with electrolysis. The hydrogen isotope trapping by this layer would have a large influence on the hydrogen isotope retention. The surface finish would be one of the effective improvement for decreasing its retention on SS.

Thermal desorption spectra of hydrogen isotopes in the monohydride phase of V–H–D and Ti–V–H–D systems

Thermal desorption of hydrogen isotopes in VH x D y ( x+ y≈0.6), Ti 0.1V 0.9H x D y ( x+ y≈0.6) and Ti 0.33V 0.67H x D y ( x+ y≈0.9) alloys has been studied by means of simultaneous measurements of thermogravimetric and differential thermal analyses and mass spectrometry. H desorbs more easily than D in all the samples studied and thus H is enriched in the gas phase during desorption. The H enrichment factor in the gas phase is in the following order, V≥Ti 0.1V 0.9>Ti 0.33V 0.67. The H enrichment factor also depends on the [H]/[D] ratio, which suggests that H and D in the solid phase influence the desorption kinetics of the other isotope probably through an indirect interaction mediated by metal atoms. The equilibrium pressure is in the order of Ti 0.1V 0.9>V>>Ti 0.33V 0.67. Deuterides have higher equilibrium pressures than protides, and this isotope effect is Ti 0.33V 0.67>Ti 0.1V 0.9≈V. There are no correlations in the isotope effects between the thermal desorption and the equilibrium pressure. Hydrogen diffusion in solids might play an important role in the thermal desorption.

Boronization in future devices – protecting layer against tritium and energetic neutrals

A thin boron film is attractive as a deuterium/tritium free wall, and as a protecting layer against impact of energetic charge-exchange neutrals in future fusion devices with long pulse operation. New experimental evidence is given for desorption of hydrogen isotopes from these films at relatively low temperature. Most hydrogen atoms in a boron-coated layer are re-emitted to the plasma side below 400°C without penetration into the substrate of stainless steel. The maintainability of a thin boron layer during a long pulse operation may be a problem. Boron atoms are hardly removed by pumping because their hydrides are easily disintegrated and redeposited. Gross migration of boron atoms inside the vessel is a concern. A condition required for avoiding the migration is discussed.

MeV He ion impact desorption of hydrogen isotopes from an InP(001)-p(1 × 1) surface

MeV He + ion impact desorption of hydrogen isotopes adsorbed on the InP(001)-p(1 × 1) surface has been studied by continuous measurements of decrease of their surface coverage by means of the elastic recoil detection (ERD) technique using a He + ion beam at different energies. It is found that the surface coverage of hydrogen decreases exponentially as the He + ion fluence increases, while no change of the p(1 × 1) spots by LEED and the In surface composition by AES has been observed even when the surface coverage decreases from 2 ML down to 0.3 ML. The desorption cross sections of MeV He + ions for hydrogen isotopes, determined from the exponential decay curves, are (8−10) × 10 −17 cm 2 in the range from 0.7 to 1.9 MeV. Their energy dependence corresponds well to that of the electronic stopping cross section for MeV He + ions of In atoms, to which the hydrogen atoms are directly bound. The desorption process of hydrogen by MeV ion impact is discussed on the basis of the experimental data.

Large Swelling of 2nd-Stage Potassium-Graphite Intercalation Compound Prepared from HOPG by Sorption and Desorption of Hydrogen Isotopes

Sorption-desorption behavior of isotopic hydrogen gases was investigated on secondstage potassium graphite intercalation compound (K-GIC) prepared from highly oriented pyrolytic graphite (HOPG) flakes. In the first run of hydrogen sorption, little amount of hydrogen was absorbed by KC21±1 at 77K, while H2 gas was absorbed up to 0.65 in the mole ratio of H2 to K in the second run. Absorbed H2 could not be desorbed even by evacuation, and was released with large swelling of the sample by warming up.The swollen sample showed dark blue color, which is characteristic of 2nd-stage K-GIC, and still had great capability of hydrogen sorption. Judging from the absorption isotherms and the data on the changes of enthalpy and entropy of absorption obtained in this study, the swollen sample was considered to have a double porous structure constructed of micropores and macropores.

Ｚｒ系合金ゲッターによる水素同位体および同位体水の吸蔵と再放出

Ｚｒ系合金ゲッターによる水素同位体および同位体水の吸蔵と再放出

Selective absorption of hydrogen isotopes in an inert gas in a zirconium particle bed

The selective absorption and recovery of hydrogen isotopes in an inert gas at 400 °C and their desorption at 800 °C were experimentally investigated using a zirconium particle packed bed. The gases used were H 2-Ar, D 2-Ar and H 2-D 2-Ar mixtures. The absorption rates of the hydrogen isotopes were found to be fast enough for this absorption method to be used as a hydrogen recovery process in the fuel cycle of a fusion reactor. The length of the absorption zone for D 2 in the zirconium bed is about twice that for H 2. The hydrogen isotopes in the H 2-D 2-Ar mixture break through in the sequence D 2, HD and H 2. This is believed to be because the absorption rate and solubility of H 2 are greater than those of D 2. The experimental results for the desorption of hydrogen isotopes are described fairly well by Fick's diffusion equation for a zirconium particle.

Absorption and desorption of hydrogen, deuterium, and tritium for Zr–V–Fe getter

Nonevaporable getters have wide applicability for developing the tritium handling techniques for thermonuclear fusion devices. From this viewpoint, mechanisms of the absorption and desorption of hydrogen isotopes and the isotope effects were investigated for a Zr–V–Fe alloy (St-707) by means of the mass analyzed thermal desorption spectroscopy. It was observed that the absorption rate was proportional to the first power of the pressure, indicating that the rate limiting step is the dissociative adsorption of hydrogen isotopes on the surface. The activation energy was very small, in the order of magnitude of a few tens of calories per mole in a temperature range from −196 to 200 °C. The desorption rate was proportional to the square of the amount of absorption, indicating that the rate limiting step is the associative desorption reaction of hydrogen atoms or ions diffused to the surface from the bulk. The rate constants for hydrogen and deuterium were determined as kd(H2)=(5.3+2.6−1.7)exp[−(28.0±0.7)×103/RT] and kd(D2)=(5.0+2.7−1.7)exp[−(28.6±0.8)×103/RT] in [1/Pa 1 s], respectively, where R is in [cal/mol deg]. With regard to tritium, the rate constant was evaluated as kd(T2)=(5.0+20−4.0)exp[−(29.3±3)×103/RT], however, the frequency factor will have to be corrected by knowing the relative sensitivity factor of the mass spectrometer for tritium (T2).

Enhanced selective hydrogen desorption from metals

The thermal desorption of hydrogen isotopes from a metal is usually a second order process the rate for which becomes asymptotically slow. We present a method for enhancing the desorption rate of one particular isotope by maintaining a constant pressure of another molecular species. This results in an effective first order desorption and concommitant exponential decay of the concentration of the selected isotope. Data is presented for the enhanced desorption of deuterium from a Zr–Al getter. The results agree well with a theoretical model, which is discussed. This enhanced desorption method should be particularly useful for tritium operation in the tokamak fusion test reactor.