Deuterium Permeation Research Articles

Deuterium Permeation in an Er2O3 Thin Film Fabricated on a Type-316L Stainless-Steel Substrate

A metal-oxide film can be used as a hydrogen-isotope permeation barrier in the fuel circulation system for nuclear fusion. We fabricated Er$_2$O$_3$ thin film on a type 316L stainless-steel substrate by using a metal-organic chemical vapor deposition technique for the purpose of hydrogen-isotope permeation barrier. Electron microscopy based imaging and energy-dispersive X-ray spectroscopy measurements indicate a sound film quality together with X-ray diffraction experiments. We also measured deuterium permeation in the film at high temperatures ranging from 600 $^{\circ}$C to 800 $^{\circ}$C. The permeation reduction was most apparent at 650 $^{\circ}$C. Above 800 $^{\circ}$C, we confirmed that the film was damaged and did not work as a permeation barrier.

The effect of surface oxides and grain sizes on the deuterium permeation behavior of niobium membranes

Group 5 transition metal niobium is considered as the promising hydrogen separation membrane material because of its theoretical highest atomic hydrogen permeability, good mechanical strength, low price and easy shaping. However, the permeability of hydrogen in the dense metal membrane is affected by surface oxides, gain sizes, defects and so on. In this paper, the effect of surface oxides and grain sizes on the permeation behavior of deuterium through niobium membranes is studied. The niobium membranes with micro- and nanocrystalline were first treated by mechanically or electro-polished to remove the surface oxides, and then the deuterium permeability tests were performed in the temperature range of 600–800 ℃ at the driving pressures of 50 kPa by gas-driven permeation method. Results showed that the niobium membrane with nanocrystalline and “clean” surface had the highest deuterium permeation than that with microcrystalline or unclean surface. More importantly, grain size and grain boundary had a greater influence on the deuterium permeation behavior of niobium membranes than the thin surface oxides. These results shed new light on the enhancement of hydrogen and its isotopes permeation in the niobium-based hydrogen separation membranes. Further work is to study the plasma-driven permeation of deuterium through nanocrystalline niobium membrane in order to obtain the super-permeation rate.

Influence of Au ions irradiation on the deuterium permeation behavior in the oxidized Fe–Cr–Al ferritic steel

Our previous study has shown that an effective tritium permeation barrier (TPB) with Al2O3 layer found could be obtained by oxidization of a Fe–Cr–Al ferritic steel. In this study, irradiation effects on deuterium permeation behavior through oxidized Fe–Cr–Al ferritic steel (OFFS) have been investigated by Au ions irradiation followed by deuterium gas driven permeation (GDP) experiments. The deuterium permeability of the irradiated and original OFFS samples has been obtained and compared. Oxide layer has been characterized by X-ray photoelectron spectroscopy (XPS) experiment and scanning electron microscopy (SEM) experiment. The defects in the oxide layer with and without Au ions irradiation have been characterized by Doppler broadening spectrometry of positron annihilation (DBS-PA) experiments. The deuterium permeation behavior of OFFS changed owing to the Au ions irradiation, which could be attributed to the increased density of vacancy-type defects.

Optimum preparation of Fe-Al/α-Al2O3 coating on 21-6-9 austenitic stainless steel

To study the formation and growth mechanism of α-Al2O3 scales, the oxidation behavior of Fe-Al diffusion coatings on 21-6-9 austenitic stainless steel has been conducted within different oxygen partial pressure (PO2) at 980 °C. The pure α-Al2O3 is evident to form with PO2 ranging from 100 Pa to 1 kPa. The growing dynamics of α-Al2O3 reveals two distinct stages including an initial linear oxidation regime and a later parabolic one. The initial oxidation rate constant is larger than that of the parabolic stage, and decreases with the increasing PO2 from 10 Pa to 1 kPa. The Volmer-Weber model is proposed to reveal the growing mechanism of α-Al2O3 scales on Fe-Al coating under different oxygen partial pressure. The deuterium permeation reduction factor (PRF) of Fe-Al/α-Al2O3 coating increased by 2–3 orders of magnitude in the temperature ranging from 450 °C to 650 °C.

Preparation and characterization of Al2O3/Y2O3 multilayer coatings as tritium permeation barrier

Tritium permeation barrier (TPB) is a promising solution to reduce fuel loss and environmental contamination caused by tritium permeation in fusion reactor. A multilayered Al2O3/Y2O3 TPB coating containing a total of 10 nanolayers was prepared by magnetron sputtering technology. The Auger electron spectroscopy, field emission scanning electron microscopy, and X-ray diffraction demonstrated the formation of the multilayer structure with crystalline Y2O3 and amorphous Al2O3 sublayers. Further, the effect of Ar/O2 flow ratio (Γ) during Al2O3 sublayer deposition on the phase structure, surface morphology, nano-hardness, corrosion resistance, He ion irradiation resistance and deuterium permeation behavior of the multilayered coating was explored systematically. The results show that the Al2O3 sublayer with lower Γ benefits the (222) preferred orientation of Y2O3 sublayer. The nano-hardness of Al2O3/Y2O3 coating gradually increases with the decrease of Γ. The coating with Γ = 1:1 performs the best corrosion resistance and He ion irradiation tolerance. The deuterium permeation test shows a lower deuterium ion current of the Al2O3/Y2O3 coating compared to their single-layer counterparts, where the deuterium gas-driven permeation process is controlled by a combination regime of recombination and diffusion. Our study could provide a potential coating material for the TPB design of fusion reactor.

Effects of oxidation on the deuterium permeation behavior of the SIMP steel

Reduced activation ferritic/martensitic (RAFM) steels are the primary candidate structural materials for the blanket in future fusion power plants. In the recent years, a novel 9–12% Cr modified F/M steel named SIMP steel has been developed. The deuterium permeation behavior of the SIMP steel with and without oxide layer has been evaluated using a gas driven permeation (GDP) device. The permeability of original and oxidized SIMP steel has been derived and compared. In order to characterize the oxide layer, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) experiments have been carried out. GDP results show that the SIMP steel has similar deuterium permeability with the CLF-1 steel. The deuterium permeability of the oxidized SIMP steel is lower than that of the original SIMP steel. Heat treatment during the oxidization process has limited influence on the deuterium permeability of the bare SIMP steel. The cross-section SEM pictures present that with the increase of the oxidation time, the thickness of the oxide layer is increased. The oxide layers are observed to be porous. The results of XRD and EDS show that the oxide layer mainly consists of chromium oxide and accumulation of chromium can be detected in the surface region. The formation of the chromium oxide on the surface of the SIMP steel could be the reason of the decrease of the deuterium permeability of the oxidized SIMP steel.

RIPER: An irradiation facility to test Radiation Induced Permeation and release of deuterium for fusion blanket materials

An efficient reduction of gaseous hydrogen isotope permeation through a metal wall is essential in several applications for the tritium inventory control of fusion energy devices. Tritium is also a safety and biological hazard and tritium losses by permeation through the materials is a critical point to be avoided to ensure safety in fusion energy. Ceramic coatings are candidates to reduce tritium permeation, into the breeder blankets of future devices, due to its low hydrogen permeation rate, excellent corrosion resistance and good mechanical properties. Furthermore, these functional materials of future fusion reactors are expected to be subjected to elevated temperature and high level of radiation fluxes and their impact on the tritium inventory has not been properly assessed mainly due to the lack of data available in the literature on this effect. Radiation induced changes in the composition and microstructure of the materials may alter tritium control in future devices. In this context, a new permeation facility “Radiation Induced Permeation” (RIPER) has been developed at CIEMAT in order to obtain relevant data on permeation of hydrogen isotopes in structural/functional materials under irradiation. This system allows one to differentiate and characterize gas concentration driven permeation, and permeation due to different parameters applied to the sample conditions like temperature, irradiation dose or electric field. The reliability of the system has been checked by means of permeation measurements for different materials in comparison with values found in literature and different measurements during irradiation have been performed. The experimental challenges of these types of measurements are reflected in this paper.

The relationship between structural changes of ceramic coatings and γ-ray irradiation effect on deuterium permeation

γ-ray irradiation effect on deuterium permeation through three kinds of ceramic coatings with different crystal structures has been investigated. Deuterium permeation flux through the coatings increased during γ-ray irradiation at 250–300 °C, but changes in the permeation flux were not detected at above 300 °C. The permeation flux through an erbium oxide coating increased due to crack formation during a permeation experiment at 500 °C. After deterioration of the coating, the γ-ray irradiation effect on permeation through the coating was similar to that of reduced activation ferritic/martensitic steel F82H substrate. On the other hand, an yttrium oxide coating had an amorphous structure and started crystallization at 500 °C. Although the irradiation effect before the crystallization was derived from the F82H substrate, the effect derived from the coating was detected after crystallization because the rate-determining process of permeation shifted to the coating. Compared to the results at 300 °C before and after crystallization, the irradiation effect decreased, proving that the ceramic coatings reduced the deuterium permeation as well as the γ-ray irradiation effect.

Preparation and properties of improved Al2O3 based MOD coatings as tritium permeation barrier

Four kinds of well-crystallized tritium permeation barrier coatings, including γ-Al2O3, α-Al2O3, γ-Al2O3/Cr2O3 and α-Al2O3/Cr2O3, were prepared by the metal organic decomposition (MOD) method using a dipping technique. In this study, we concentrated on the preparation and properties of α-Al2O3 and α-Al2O3/Cr2O3 double-layer coatings. The results showed that the α-Al2O3 coating exhibited a pure phase structure, which was entirely and directly transformed from the γ-Al2O3 at an annealing temperature of 1000 °C, and no obvious substrate oxides were formed. An unannealed Cr2O3 MOD layer with a thickness of 0.8 μm featured higher crystallization and was taken as a buffer layer. However, the template effect of Cr2O3 was not obvious because the formation temperature of the α-Al2O3 did not decrease. The corrosion resistance (1.068 × 10−7 A/cm2) and nanohardness (18.49 GPa) of the α-Al2O3/Cr2O3 double-layer coating improved compared to those of γ-Al2O3, α-Al2O3, and γ-Al2O3/Cr2O3 coatings. In contrast, the deuterium permeation test showed that the α-Al2O3 MOD coating had the lowest deuterium ion current at temperatures of 400 ˜ 600 °C of the films considered in this study, demonstrating better resistance to deuterium permeation. Relevant mechanisms and explanations are discussed in detail.

Oxide layer formation in reduced activation ferritic steel F82H under DEMO reactor blanket condition

Tritium permeation through structure materials in fusion blanket systems is a critical issue from the perspectives of fuel loss and radiological hazard. In the previous studies, detailed hydrogen isotope permeation behaviors in reduced activation ferritic/martensitic steels have been investigated; however, oxidation of the steel surface is expected under an actual DEMO reactor condition, and then the tritium permeation behavior will be changed. In this study, deuterium permeation through the steels heat-treated under simulated environment conditions has been investigated for more precise predictions of tritium loss at DEMO reactor blankets. Reduced activation ferritic/martensitic steel F82H substrates were heat-treated in helium gas flow containing 1 vol% hydrogen at 300, 400 and 500 °C for 100 and 200 h to simulate a solid breeder DEMO reactor blanket condition. After surface observation and analysis for the heat-treated samples, gas-driven deuterium permeation measurements were performed. An iron oxide layer was formed on the sample surface, and the thickness of the layer was 50 nm‒12 μm. The oxide layer on the sample surface heat-treated at 500 °C for 100 h decreased deuterium permeation by a factor of 5. After the permeation tests, dissipation of the oxide layers was confirmed.

Estimation and Mode Selection of Deuterium Flux Supply into Ampoule Device Through Diffusion Filter in Experiments with Pb15.7Li Eutectic at the IVG1.M Reactor

One of the most promising materials to produce tritium in fuel cycle of fusion facilities is the lead-lithium eutectic Pb15.7Li. Tritium will be generated in nuclear reactions in a lithium-containing material under the influence of neutron irradiation. However, nowadays a limited number of studies have been conducted with the eutectic of such a composition (with a lithium content of 15.7%) and consequently, there is a lack of data on mechanisms of tritium generation and release from Pb15.7Li. In this regard, there is an urgent necessity for research of tritium generation and release from Pb15.7 Li directly under neutron irradiation conditions. For these studies a differential method will be used, which consists in follows: a controlled flux of spectrally pure deuterium will be continuously fed into the experimental cell with the eutectic sample during the reactor experiment. The regulated flux of deuterium will be fed to the experimental cell with the Pb15.7Li sample using diffusion palladium-silver filter. The article describes the process of determination of deuterium flux supply modes into the experimental cell. The temperature dependences of deuterium penetration through diffusion palladium-silver filter are presented. The coefficients of diffusion, solubility and permeability of deuterium through a palladium-silver filter are estimated and the activation energies of these processes as well as the Arrhenius dependence are presented.

Comparison of the hydrogen permeation through fusion relevant steels and the influence of oxidized and rough surfaces

Abstract The development and application of tritium permeation barriers (TPB) are crucial for safe and economical fusion reactor operation. In order to specify the requirements and important characteristics of TPB, the deuterium permeation flux through two different fusion relevant steels, namely Eurofer97 and 316L(N)-IG, were measured and compared. Furthermore, the influence of oxidized and rough surfaces on the deuterium permeation flux was investigated. With this study, the influence of technical or plasma roughened surfaces on the permeation behavior can be estimated.

Effect of Steel Substrates on the Formation and Deuterium Permeation Resistance of Aluminide Coatings

The effect of steel substrates on the formation and deuterium permeation resistance of aluminide coatings for tritium permeation barrier applications was investigated. It was found that the average thickness and crystal structure of electrodeposited Al coatings varied with Cr steel substrates. After aluminization in vacuum, significant differences existed in the composition and thickness of (Fe,Cr)2Al5-type aluminide layers formed on different Cr steel substrates, in which the alloying element Cr from steel substrates was involved. Thereafter, the scale microstructural feature and thickness also changed with the Cr steel substrate after selective oxidation in an Ar gas stream. Consequently, the deuterium permeation resistance of the formed aluminide tritium permeation barriers (TPBs) differed by steel substrates, indicating that the substrate effect existed in aluminide TPB coatings and thus could have a significant influence on the formation and eventual performance of aluminide TPBs.

Surface oxidation effect on deuterium permeation in reduced activation ferritic/martensitic steel F82H for DEMO application

Fuel loss and environmental contamination by tritium permeation through structural materials are critical issues for the establishment of a fusion DEMO reactor. In this study, the effectivity of a chromium oxide layer formed on reduced activation ferritic/martensitic steel F82H as a tritium permeation barrier and its stability under simulated solid/liquid breeder blanket conditions have been investigated. A uniform 100-nm-thick chromium oxide layer was formed by heat treatment at 710 °C for 5 min in 50% argon-50% hydrogen mixed gas with the flow rate of 200 standard cubic centimeter per minute. After exposure to simulated solid breeder blanket conditions, an iron oxide layer and a spinel-type iron-chromium oxide layer formed. In the case of a liquid breeder blanket condition, the chromium oxide layer partly lost at 500 °C for 100 h. The chromium oxide-formed sample decreased deuterium permeation flux by a factor of up to 150. The permeation reduction efficiency deteriorated after exposure to a solid breeder blanket condition due to a change of the chromium oxide layer. However, the chromium oxide formation would play a role to reduce hydrogen isotope permeation even after reduction of the oxide layers.

Experimental refutation of the deuterium permeability in vanadium, niobium and tantalum

Deuterium permeability through Nb, V, and Ta was measured in the temperature range between ∼300-500 °C and 100–1000 mbar. For the three materials, the permeation rate at 500 °C was between two and torders of magnitude below expected values which were obtained by combining diffusivity and solubility data and which have been traditionally accepted due to the insufficient experimental available data. Comparison with existing literature suggests a complex dependence of permeability with temperature, which helps explain this discrepancy. Given the important role of the surface condition on the permeability, additional deuterium permeation tests were carried out in vanadium for more realistic sample preparation. Results indicate that native oxides formed at room temperature introduce a permeation reduction of several orders of magnitude, and must be considered for practical applications.

A Dense Cr2O3/Al2O3 Composite Ceramic Coating Prepared by Electrodeposition and Sealing with Al2O3

A dense Cr2O3/Al2O3 composite coating was fabricated on 321L stainless steel by electrodepositing an Al2O3 layer on a Cr2O3 coating. The composition, structure, and properties of the obtained ceramic coating were investigated. The results showed that Al2O3 fully infiltrated the Cr2O3 coating and significantly improved the compactness of the ceramic coating by filling in the pores and cracks between the Cr2O3 grains. The composite ceramic coating was heat-treated at 750 °C and exhibited a high microhardness of 219.4 HV500g, a bonding strength of 46.5 MPa, and excellent anti-corrosion and deuterium permeation suppression properties.

Influence of the grain structure of yttria thin films on the hydrogen isotope permeation

Steel components are required in the infrastructure and the facilities of the hydrogen economy. The high hydrogen pressures in the hydrogen economy lead to embrittlement and surface corrosion of the steels. For the functionality of the facilities it is necessary to suppress the embrittlement and the surface corrosion of the steels by protective layers, e.g. ceramic thin films. With regard to fusion power plants ceramic thin films on the structural steel materials are also required. These thin films work as a tritium permeation barrier that is necessary to prevent the loss of the radioactive fuel inventory. Oxide thin films, e.g. Al2O3, Er2O3, and Y2O3, are promising candidates as tritium permeation barrier layers. In terms of the application in the first wall, this is especially true for yttrium due to its favorably short decay time after neutron activation compared to the other candidates. The Y2O3 layers with thicknesses of 0.5 μm–1 μm are deposited on both substrate sides by RF magnetron sputter deposition. Since the microstructure of the barrier layer plays an important role for the permeation reduction, layers with three different magnetron process modes and thus three different microstructures are prepared. After annealing the cubic crystal structure of all thin films is verified by X-ray diffraction and the different microstructures are investigated by scanning electron microscopy and transmission electron microscopy. The Y2O3 stoichiometry of all thin films and a chromium oxide material segregation at the interface are verified by analysis methods such as X-ray photoelectron spectroscopy. The permeation reduction factors of all thin films are determined in gas-driven deuterium permeation experiments. Corresponding to the three different microstructures, reduction factors of 25, 45, and 1100 are identified. Thus, the permeation reduction is strongly dependent on the Y2O3 microstructure. The measurement results suggest that a high density of grain boundaries leads to a high hydrogen permeation.

Radiation effects on deuterium permeation for PLD alumina coated Eurofer steel measured during 1.8 MeV electron irradiation

Tritium permeation through structural materials in future fusion reactors is an extremely important issue due to both radiological concerns and tritium self-sufficiency. In the past many efforts to minimize tritium losses have been made and permeation barriers are considered the best method to reduce them. Alumina is one of the main candidates for such barriers due to its chemical stability and hydrogen isotope permeation reduction factor. In this work pulsed laser deposited (PLD) alumina on Eurofer steel has been studied in terms of deuterium permeation. A reduction factor of about 1000 compared to bare material in the temperature range RT-450 °C was measured. In order to study deuterium permeation during irradiation the Radiation Induced Permeation and Release (RIPER) facility at Ciemat was used. Contrary to expectations the permeation through PLD alumina coated Eurofer was observed to decrease during irradiation. This radiation effect was explained making use of thermostimulated desorption (TSD) experiments. TSD measurements were carried out for both electron irradiated and unirradiated alumina samples and the results showed that radiation induced deuterium back desorption from alumina occurred in this way reducing the overall permeation value during irradiation. Finally, the microstructural study of the irradiated coatings showed that some surface damage appears but not cracking or coating debonding was observed in agreement with the good behaviour observed in terms of deuterium permeation for the irradiated coatings.

The effect of γ-ray irradiation on deuterium permeation through reduced activation ferritic steel and erbium oxide coating

Deuterium permeation through a fusion-relevant ferritic steel F82H with and without erbium oxide coatings under γ-ray irradiation has been investigated in a temperature range from 300 to 700 °C. The deuterium permeation flux through F82H sample increased by γ-ray irradiation at lower temperatures below 450 °C. The irradiation effect increased with dose rate, and the percentage of the permeation flux gain might be several percent under the dose rate of a few Gy s‒1. Temperature of the F82H sample surface rose by about 0.5 °C depending on the dose rate, and so the γ-ray irradiation effect is mainly attributed to γ-heating. On the other hand, at higher temperature above 500 °C, no appreciable change of the deuterium permeation was observed. Similarly, the deuterium permeation flux through erbium oxide coated samples increased under γ-ray irradiation at lower temperatures (350‒450 °C), but no appreciable change of permeation flux through coatings was observed at higher temperatures (600‒700 °C). The coating surface temperature increased at lower sample temperatures by γ-heating.

Efficient hydrogen and deuterium permeation reduction in Al2O3 coatings with enhanced radiation tolerance and corrosion resistance

One of the major bottlenecks in the development of the breeding blanket of the DEMO fusion reactor is the suppression of tritium permeation through structural steels as well as their protection against dissolution-corrosion by interaction with high temperature heavy liquid metals. Reduction of tritium permeation and corrosion of structural steels are crucial issues in order to enhance reactor safety and avoid operational implications. As a solution to these two daunting challenges, we developed multifunctional alumina coatings capable to tackle, at the same time, tritium permeation and Pb–Li corrosion. The coatings are deposited by pulsed laser deposition and are essentially amorphous, with nanocrystalline inclusions. By optimizing the deposition process, we provide experimental evidence that PLD-grown alumina yields a permeation reduction factor for hydrogen and deuterium well above 104, even after electron irradiation, and a suitable protection against corrosion by the Pb–16Li eutectic. Given these results, the multifunctional, PLD-grown alumina coatings stand out as a viable solution to some of the long-lasting issues related to fusion technologies.