Transport Of Hydrogen Isotopes Research Articles

Hydrogen isotope transport across tungsten surfaces exposed to a fusion relevant He ion fluence

Tungsten targets are exposed to controlled sequences of D2 and He, and He and D2 plasma in the Pisces-A linear plasma device, with a view to studying the outward and inward transport of D across a He implanted surface, using thermal desorption mass spectrometry. Differences in transport are interpreted from changes in peak desorption temperature and amplitude for D2 release, compared against that of control targets exposed to just D2 plasma. Desorption data are modeled with Tmap-7 to infer the nature by which He leads to the ‘reduced inventory’ effect for H isotope uptake. A dual segment (surface-30 nm, bulk) W Tmap-7 model is developed, that simulates both plasma exposure and thermal desorption. Good agreement between desorption data and model is found for D2 release from control targets provided that the implanted flux is reduced, similar to that reported by others. For He affected release, the H isotope transport properties of the surface segment are adjusted away from control target bulk values during the computation. Modeling that examines outward D transport through the He implanted layer suggests that a permeation barrier is active, but bubble induced porosity is insufficient to fully explain the barrier strength. Moderately increased diffusional migration energy in the model over the He affected region, however, gives a barrier strength consistent with experiment. The same model, applied to inward transport, predicts the reduced inventory effect, but a further reduction in the implanted D flux is necessary for precise agreement.

A study on hydrogen isotopes transport in a liquid metal GaInSn by plasma-driven permeation method

The application of liquid metals such as gallium, tin and lithium as plasma-facing materials is a potential means to resolve the technical issues associated with power exhausting and particle handing in magnetic fusion devices. GaInSn alloy with melting point of 10.5°C, is employed as a modeling material to explore the plasma-driven permeation (PDP) method to study the hydrogen isotopes (hydrogen and deuterium) transport parameters in a liquid metal. Static liquid GaInSn membranes sitting on a mesh sheet are exposed to hydrogen/deuterium plasmas in the linear plasma device VEHICLE-1 with the temperature range of 280–496°C. Hydrogen/deuterium diffusivity are obtained by fitting the time evolutions of permeation fluxes. The dynamic hydrogen/deuterium retention in the liquid GaInSn are found to be low (∼1015D/cm3), which are consistent with the thermal desorption spectroscopy (TDS) measurement following plasma exposure. The hydrogen and deuterium transport parameters are found to be close to each other.

Effect of multisite traps on hydrogen transport in solids

The transport of hydrogen isotopes in solids is an important problem for a series of applications, in particular, for future thermonuclear reactors. The main processes determining transport are the diffusion of dissolved hydrogen and its interaction with lattice defects. It is known that vacancies in a metal can capture not only one hydrogen atom, but several at the same time. General equations describing hydrogen transport in this case are presented. Special attention is focused on the influence of this effect on the thermal desorption spectra. An experimental scheme making it possible to establish the capture of several atoms to traps is proposed.

Gas-driven permeation of deuterium through tungsten and tungsten alloys

To address the transport and trapping of hydrogen isotopes, several permeation experiments are being pursued at both Sandia National Laboratories (deuterium gas-driven permeation) and Idaho National Laboratories (tritium gas- and plasma-driven tritium permeation). These experiments are in part a collaboration between the US and Japan to study the performance of tungsten at divertor relevant temperatures (PHENIX). Here we report on the development of a high temperature (≤1150°C) gas-driven permeation cell and initial measurements of deuterium permeation in several types of tungsten: high purity tungsten foil, ITER-grade tungsten (grains oriented through the membrane), and dispersoid-strengthened ultra-fine grain (UFG) tungsten being developed in the US. Experiments were performed at 500–1000°C and 0.1–1.0atm D2 pressure. Permeation through ITER-grade tungsten was similar to earlier W experiments by Frauenfelder (1968–69) and Zaharakov (1973). Data from the UFG alloy indicates marginally higher permeability (<10×) at lower temperatures, but the permeability converges to that of the ITER tungsten at 1000°C. The permeation cell uses only ceramic and graphite materials in the hot zone to reduce the possibility for oxidation of the sample membrane. Sealing pressure is applied externally, thereby allowing for elevation of the temperature for brittle membranes above the ductile-to-brittle transition temperature.

Hydrogen-isotope transport in an ELBRODUR G CuCrZr alloy for nuclear applications in heat sinks

We present the first complete data set of the transport parameters (permeability, diffusivity, and solubility) of hydrogen and deuterium in an ELBRODUR G precipitation hardened CuCrZr alloy experimentally measured by using the time-dependent gas-phase technique in an elevated temperature range of 300–600 °C for nuclear applications in heat sinks. Using the measured values for hydrogen and deuterium and a quantum mechanical model based on a harmonic approximation, an extrapolation for tritium is also presented. The isotope effect ratios for the transport parameters were also estimated. Furthermore, our hydrogen results for ELBRODUR G were compared with the results for other copper alloys previously reported by other authors.

Features of hydrogen trapping and desorption during deposition of yttrium coating on zirconium in a gas discharge

Transport of hydrogen isotopes during the various regimes of deposition of yttrium coating on zirconium in argon plasma with addition of deuterium is studied. The influence of oxygen contamination in plasma-generating gas on the processes of trapping and desorption of hydrogen isotopes is also investigated. It is shown that deposition of yttrium coating on zirconium in Ar+5%D2 plasma enhances both hydrogen desorption from zirconium and deuterium trapping into zirconium in comparison to those under plasma exposure without deposition. Yttrium deposition in Ar+25%O2+5%D2 plasma, conversely, mitigates both hydrogen desorption and deuterium trapping. Hydrogen desorption from zirconium increases with the increase of energy of ions, bombarding the sample during deposition of the coating in oxygen-free plasma, but it, on the contrary, decreases in oxygen-containing plasma.

Hydrogen isotope dissolution, diffusion, and permeation in Er2O3

We report the fabrication and characterization of nanocrystalline Er2O3 thin films, as well as the calculations of interstitial deuterium (D) behaviors in bulk Er2O3 using first-principles calculations based on density-functional theory. Our results show that the prepared Er2O3 thin films possess a regular cubic phase with a phase structure consisting mainly of bulk and grain boundaries. Transport of hydrogen isotopes in bulk is predicted to occur by translocation between empty interstitials (e.g., tetrahedral or octahedral sites), and involves hopping from one empty interstitial to another. The rate-determining process of diffusion and permeation is hydrogen isotope movement from tetrahedral site to octahedral site. Transport of hydrogen isotopes within grain boundaries is predicted to be dominant based on the comparison of D permeability or permeation activation energy between experiments and DFT calculations. At a typical temperature of 873 K, the solubility, diffusion coefficient, and permeability of D in bulk Er2O3 are predicted to be 2.94 × 10−15 mol m−3, 3.56 × 10−10 m2 s−1, and 3.68 × 10−27 mol m−1 s−1 Pa−1/2, respectively.

Effects of surface thermodynamics on hydrogen isotope exchange kinetics in palladium: Particle and flow models

Palladium is an important material for separation of hydrogen from other gases, separation of hydrogen isotopes, and for hydrogen storage. Its main advantages are its high selectivity and rapid, highly reversible uptake and release of hydrogen at near-ambient temperatures and pressures. Toward a more comprehensive understanding of its behavior, we present particle and continuum multiphysics mathematical models of the coupled reactive transport of hydrogen isotopes in the context of a single palladium sphere, and of flow in a packed palladium hydride bed. The models consider rates of chemical reactions and mass transport within a hydride bed, and incorporate a multistep reaction mechanism involving the metal bulk, metal surface, and gas phases. A unique feature in this formulation is that the chemical reaction model accounts for all absorption, adsorption, and diffusion activation energies. In particular, the adsorption energy is believed to depend strongly on the composition and atom-scale structure of the surface. We perform a parametric study to evaluate the effects of temperature, surface adsorption energy, and hydride particle radius on the isotope exchange kinetics. The models are useful in designing optimal hydride beds operating at various temperatures, with varied hydride particle size, and surface conditions.

Laboratory Experiments and Modeling on Bi-Directional Hydrogen Isotopes Permeation through the First Wall of a Magnetic Fusion DEMO Reactor

The first wall of a magnetic fusion DEMO reactor serves to separate the edge plasma from breeding blanket, the latter of which is required to operate at elevated temperatures. To minimize the thermo-mechanical stress, the wall thickness is often limited to be less than 1 cm. As a result, the first wall is subjected to hydrogen isotopes permeation in the two opposite directions via plasma-driven permeation (PDP) by D+ (or D0) and T+ (or T0) in the edge plasma region and via gas-driven permeation (GDP) by T2 bred in the blanket. In the present work, the bi-directional hydrogen permeation behavior through a candidate first wall material, F82H, has been studied, using a laboratory-scale plasma device. Experimental data indicate that GDP tends to dominate the overall hydrogen isotopes transport. The effects of surface roughness and contamination on PDP have been investigated. Also, a one-dimensional diffusion code has been used to simulate bi-directional PDP and GDP under reactor-relevant conditions where multiple hydrogen isotopes flow through the first wall.

The effect of a micro bubble dispersed gas phase on hydrogen isotope transport in liquid metals under nuclear irradiation

The present work intend to be a first step towards the understanding and quantification of the hydrogen isotope complex phenomena in liquid metals for nuclear technology. Liquid metals under nuclear irradiation in, e.g., breeding blankets of a nuclear fusion reactor would generate tritium which is to be extracted and recirculated as fuel. At the same time that tritium is bred, helium is also generated and may precipitate in the form of nano bubbles. Other liquid metal systems of a nuclear reactor involve hydrogen isotope absorption processes, e.g., tritium extraction system. Hence, hydrogen isotope absorption into gas bubbles modelling and control may have a capital importance regarding design, operation and safety.Here general models for hydrogen isotopes transport in liquid metal and absorption into gas phase, that do not depend on the mass transfer limiting regime, are exposed and implemented in OpenFOAM® CFD tool for 0D–3D simulations. Results for a 0D case show the impact of a He dispersed phase of nano bubbles on hydrogen isotopes inventory at different temperatures as well as the inventory evolution during a He nucleation event. In addition, 1D and 2D axisymmetric cases are exposed showing the effect of a He dispersed gas phase on hydrogen isotope permeation through a lithium lead eutectic alloy and the effect of vortical structures on hydrogen isotope transport at a backward facing step.Exposed results give a valuable insight on current nuclear technology regarding the importance of controlling hydrogen isotope transport and its interactions with nucleation event through gas absorption processes.

Plasma- and Gas-Driven Hydrogen Isotope Permeation Through the First Wall of a Magnetic Fusion Power Reactor

The first wall of a magnetic fusion power reactor is defined essentially as the plasma-facing walls of blankets. For the high temperature operation of self-cooled breeder blankets, the first wall is often designed to be less than 1cm thick to reduce mechanical stresses and as a result will be subjected to bi-directional hydrogen permeation by two distinctive mechanisms; in one direction by edge plasma-driven and in the other direction by bred tritium gas-driven permeation. Using a laboratory-scale plasma device and a one-dimensional diffusion model, plasma-driven and gas-driven hydrogen permeation behavior has been investigated under some of the conditions relevant to FLiBe-employed blankets. For a 5mm F82H membrane, the plasma-driven permeation flux at ~500 °C and the gas-driven hydrogen permeation flux at ~350 °C have been measured to be of the orders of 1013 H-atoms/cm2/s and 1014 H-atoms/cm2/s, respectively. From these data one predicts that gas-driven permeation could dominate the hydrogen isotope transport through the first wall.

Effect of radiation-induced damage on deuterium retention in tungsten, tungsten coatings and Eurofer

An influence of radiation-induced damage on hydrogen isotope retention and transport in a bulk tungsten (W), dense nano-structured W coatings and Eurofer was investigated under well-defined laboratory conditions. Radiation-induced defects in W materials and Eurofer were created by irradiation with 20MeVW ions. Following the damage production, samples were exposed to low-energy deuterium plasma. The deuterium (D) retention in each sample was subsequently measured by nuclear reaction analysis (NRA) for the depth profiling up to 6μm. It was shown that the D retention at radiation-induced damage is almost equivalent for different W grades after irradiation at high enough fluence. The kinetic of D migration and trapping in damaged area as well as recovery of radiation-induced damage were investigated by loading at different temperatures. It was shown that deuterium retention in tungsten in fusion environment will be dominated by radiation-induced effect in a wide range of investigated temperatures, namely, from room temperature to 1100K. Whereas displacement damage produced in Eurofer has less pronounced effect on the deuterium accumulation.

Investigating permeation and transport of H isotopes in tungsten by first-principles

We have investigated permeation and transport of hydrogen (H) isotopes in tungsten (W) single crystal employing first-principles calculations in junction with Fick’ law. Permeability was approximately evaluated according to the solubility and diffusion coefficient of H. The solubility for H in bulk W from present calculation is consistent with the experimental results measured by Frauenfelder. The permeation fluxes of H isotopes are examined at the different thickness of W wall. The permeation fluxes of deuterium with the W thickness of 21μm at the temperature of 770K and with the W thickness of 50μm at the temperature of 893K were 0.68×1013 atom/m2s and 0.34×1014 atom/m2s, respectively. The dissociation coefficients of H isotopes are also evaluated. We believe that the present first-principles combined with Fick’ law method can be also generalized to investigate permeation and transport of H isotopes in most metals since such H isotopes behaviors in most metals are similar to those of H isotopes in W.

Hydrogen transport and trapping in the GlidCop Al25 IG alloy

The hydrogen properties of permeability, diffusivity and Sieverts’ constant in the GlidCop Al25 IG alloy have been experimentally evaluated by using the gas permeation technique. The experimental temperature range used has been from 573 K to 793 K and the high purity hydrogen loading pressures from 10 3 Pa to 1.5 × 10 5 Pa. The resultant diffusive transport parameters are a permeability of Ф (mol m −1 Pa −1/2 s −1) = 5.87 × 10 −7 exp(−80.6 kJ mol −1/ RT), a diffusivity of D (m 2 s −1) = 5.70 × 10 −5 exp(−76.8 kJ mol −1/ RT) and a Sieverts’ constant of K s (mol m −3 Pa −1/2) = 6.01 × 10 −3 exp(−3.7 kJ mol −1/ RT). The resultant trapping parameters are a trap density of N t = 3.1 × 10 22 m −3 and a trapping energy of E t = 75.4 kJ mol −1. The presence of ultrafine Al 2O 3 particles in this material has been demonstrated to affect enormously the hydrogen isotope transport behaviour in comparison to the corresponding base material (Cu) and other copper alloys. Hydrogen trapping phenomenon has become more noticeable in the lower temperature range, yielding an exothermic absorption of hydrogen below 688 K and a decrease in the effective hydrogen diffusivity.

Dynamic Monte-Carlo modeling of hydrogen isotope reactive–diffusive transport in porous graphite

An equal mixture of deuterium and tritium will be the fuel used in a fusion reactor. It is important to study the recycling and mixing of these hydrogen isotopes in graphite from several points of view: (i) impact on the ratio of deuterium to tritium in a reactor, (ii) continued use of graphite as a first wall and divertor material, and (iii) reaction with carbon atoms and the transport of hydrocarbons will provide insight into chemical erosion. Dynamic Monte-Carlo techniques are used to study the reactive–diffusive transport of hydrogen isotopes and interstitial carbon atoms in a 3-D porous graphite structure irradiated with hydrogen and deuterium and is compared with published experimental results for hydrogen re-emission and isotope exchange.

Multi-scale modeling of hydrogen isotope transport in porous graphite

We describe a general multi-scale method to model hydrogen isotope transport, over length scales from angstroms to centimeters and time scales from picoseconds to several seconds, in a complex three-dimensional porous geometry using molecular dynamics, kinetic Monte Carlo and Monte Carlo diffusion simulations. we present comparisons with experimental results for hydrogen diffusion and hydrogen atom desorption from graphite. Finally, we demonstrate the flexibility of the computational tools used to tackle problems at different scales.

Measurement of the transport of hydrogen isotopes near the surface of metal-hydride and deuteride using elastic recoil detection technique

The thermal behavior of hydrogen isotopes near the surface of δ-phase titanium hydride and deuteride covered with an oxide layer has been investigated using the elastic recoil detection (ERD) technique. The hydrogen isotopes concentrations near to the surface of the hydride and deuteride decreased exponentially as a function of annealing time in the temperature range of 423–488K. Also a hydrogen concentration gradient is formed at the surface. The change of the hydrogen distribution with annealing time at several temperatures was analyzed using mass balance equations in which elementary processes such as diffusion, trapping and detrapping at vacant trap sites are taken into account. The effective diffusion rates of hydrogen isotopes to the topmost oxide layer and thermal detrapping rates of hydrogen isotopes at the hydride–oxide interface were estimated. Moreover, the activation energies for the effective diffusion rate and the thermal detrapping rate were determined to be 0.54±0.10 and 1.20±0.02eV, respectively.

Multi-scale modeling of hydrogen isotope transport in porous graphite

We present a multi-scale model for hydrogen isotope transport in graphite. We use molecular dynamics (MD) simulations to study hydrogen isotope transport in a graphite micro-crystal which is a few nanometers in size. The MD results are parametrized in a Kinetic Monte Carlo (KMC) model as a diffusion process of two competing thermally activated events. Micro-crystal diffusion coupled with a trapping–detrapping model at microvoids has then been used in a KMC model to simulate diffusion across a granule which is typically a few microns in size. Finally we extend these models to the centimeter scale and present initial results for hydrogen isotope transport in 3d, porous graphite.

Transport and exchange of hydrogen isotopes in silicon-device-related stacks

Thermally driven transport and exchange of hydrogen and deuterium in silicon-based metal-oxide-semiconductor (MOS) device-related structures were experimentally investigated using elastic recoil detection analysis. The samples were planar stacks of different materials on crystalline silicon. The materials studied included silicon oxide prepared by thermal growth, polycrystalline silicon silicon nitride, silicon oxynitride, and borophosphosilicate glass (BPSG) prepared by chemical vapor deposition (CVD). CVD was performed using either standard (hydrogen-containing) or deuterated precursors. Thermal annealing was carried out at 350–800 °C for 10–300 min in argon or in forming gas, either standard (90 vol. % N2,10 vol. % H2) or deuterated. All materials except silicon nitride were permeable to hydrogen and deuterium in the temperature range studied. Isotope exchange in the polycrystalline Si/SiO2 structure was observed above 450 °C. BPSG showed very little relative isotope exchange. Implications to MOS device processing are discussed.

Tritium diffusive transport parameters and trapping effects in the reduced activating martensitic steel OPTIFER-IVb

A time-dependent gas-phase isovolumetric desorption technique has been used to obtain the hydrogen isotopes transport parameters between 423 and 892 K and driving pressures ranging from 4×10 4 to 1×10 5 Pa. For protium and deuterium the properties diffusivity ( D), Sieverts’ constant ( K s), permeability ( Φ), trapping energy ( E t) and the trap sites concentration ( N t) are given. On the basis of ideal harmonic vibration of the hydrogen isotope atoms in a unique type of solution site, the values derived for the characteristic protium oscillation temperatures are: θ=1884 K, θ *=2387 K. These values lead to the following extrapolated tritium transport parameters: D ( m 2 s −1)=4.166×10 −8 exp (−12 027/RT), K s ( mol m −3 Pa −1/2)=0.271 exp (−27 905/RT) , Φ ( mol m −1 Pa −1/2 s −1)=1.127×10 −8 exp (−39 933/RT), E t ( J/ mol)=55 554, and N t ( sites/ m 3)=0.79×10 24 . The dynamics of the hydrogen isotopes transport and the origin of the trapping phenomenon are discussed in connection with the OPTIFER-IVb microstructure.