Deuterium Permeation Flux Research Articles

Formation of hydrogen resistant oxides of titanium alloy in water corrosion environment

The structure changes and hydrogen permeation behavior of Titanium alloy TA17 in simulated water environment of small modular reactor (SMR) at 320°C for 8000h was investigated. We found a corrosion layer consist of TiO2 and FeTiO3 with a good hydrogen permeation resistance. The structure and hydrogen permeation resistance change with the increase of corrosion period. At the first corrosion period of 3000h, FeTiO3 grows rapidly with an exponential parameter of 0.663 fitted by parabolic law. As the initial TiO2 layer destroyed, the deuterium permeation flux increases. After the thickness of FeTiO3 reaches a limit at corrosion time of 4000h, there exists a dynamic balance between the growth and the dissolution of FeTiO3, result in a small fluctuant deuterium permeation flux at corrosion periods of 5000－8000h. The deuterium permeation flux of the corrosion layer can be two orders of magnitude lower to that of Titanium alloy TA17 substrate. The formation process of corrosion layer and its effect on hydrogen permeation resistance are discussed in detail.

Preparing high performance FeAl/Al2O3 coating as tritium permeation barrier

Preparation of tritium permeation barrier (TPB) coating on the surface of structural materials is one of the most effective solutions to solve the issue of tritium permeation in tritium breeder blanket. The FeAl/Al2O3 coating is considered as the most promising candidate material for TPB coating due to its low hydrogen isotopes permeability, good adhesion and excellent radiation resistance. However, the current reported performance of FeAl/Al2O3 coating is much lower than its theoretical value. This work proposed a three-step process to prepare FeAl/Al2O3 TPB coating. By magnetron sputtering deposition, aluminizing and in-situ oxidation, a layer of high quality γ-Al2O3 about 250 nm thick was successfully formed on the 304 stainless steels. The Al2O3 layer was dense and no obvious defects were found. The gas-driven permeation measurements showed that the coating sample had strong ability to inhibit deuterium permeation, where the deuterium permeation flux was reduced by 5 orders of magnitude compared to the uncoated one at 600 °C, which is the best reported performance. Meanwhile, the thermal shock resistance test showed that the coating had no cracks after 50 thermal cycles. Moreover, the coating had a high electrical resistivity of approximately 3.42 × 1014 Ω cm, which could effectively reduce the magneto-hydrodynamic pressure drop (MHD) effects.

Deuterium permeation and lithium‑lead corrosion behaviors of ceramic‑iron joint coating

In fusion reactor blanket design, the main challenges are to control the permeation of tritium and prevent the corrosion of the structural materials. This study focuses on investigating the behavior of ceramic‑iron joint coatings in terms of deuterium permeation and Li-Pb corrosion aiming to develop effective barriers against permeation while providing corrosion protection. The research involved fabricating ZrO2 and Fe2O3 ceramic coatings on F82H steel substrates using metal-organic decomposition followed by joining the coated samples with Fe foils using a hot press machine. Deuterium permeation measurements were conducted to assess the effectiveness of the coating, and liquid Li-Pb exposure tests in a flow environment were performed to evaluate its resistance against corrosion. The results showed that the coating reduced deuterium permeation flux by a factor of 2000 at 400 °C and 7000 at 550 °C compared to uncoated samples suggesting an improved crystallinity or grain growth without degradation due to the joining process. Furthermore, the corrosion layers formed on the surface of the Fe layer after the flowing Li-Pb exposure test. Although this layer gradually decreased in thickness over time while not significantly affecting the underlying Fe layer's thickness. This observation indicates that the corrosion layer performed mitigating the corrosion rate of the Fe layer. This paper aims to demonstrate how ceramic‑iron joint coatings can be compatible with the advanced fusion reactors.

Deuterium permeation behavior of zirconium oxide coating after exposure to solid breeder pebbles

Tritium permeation barrier has been developed using ceramic coatings to mitigate tritium leakage through structural materials in most of the fusion reactor blanket concepts. In a solid breeder blanket concept, corrosion of the coating is a serious issue in addition to tritium permeation; however, the effects of corrosion on tritium permeation have been rarely researched. Here, we report deuterium permeation behaviors of zirconium oxide coatings prepared by metal organic decomposition after exposure to two kinds of solid breeder pebbles with different compositions, followed by deuterium permeation measurements. The deuterium permeation flux varied with the pebble composition: the coated sample after exposure to the pebbles of 30 mol% lithium metatitanate and 70 mol% lithium orthosilicate was smaller than that after exposure to the pebbles of 20 mol% lithium metatitanate and 80 mol% lithium orthosilicate. Because the thickness of the corrosion layer formed by the pebbles with 30 mol% lithium metatitanate and 70 mol% lithium orthosilicate was larger, the composition of the pebbles affected the thickness of the corrosion layer and the permeation behaviors rather than coating integrity.

The effects of heavy-ion irradiation on electrical properties and hydrogen isotope permeation behavior of ceramic coatings

Tritium permeation through structural materials in fusion reactor blanket systems is a crucial problem in terms of fuel efficiency and radiological safety. A tritium permeation barrier has been developed using ceramic coatings for several decades to mitigate tritium leakage. Recent studies are focused on irradiation effects on microstructure and hydrogen isotope permeation behavior of the coatings. However, most of the analytical methods used in these studies were destructive and time-consuming, which is undesirable to apply to the actual reactor components. Here, we report the influence of irradiation damage on electrical properties and deuterium permeation behaviors of ion-irradiated zirconium oxide coatings fabricated by metal organic decomposition to develop a convenient approach for coating characterization. The undamaged and irradiated coatings decreased the deuterium permeation flux by a factor of more than 1000 in comparison with an uncoated substrate at 300 °C. The irradiated coatings had lower permeation flux than the undamaged coatings, suggesting that irradiation-induced grain growth reduced deuterium permeation. While the undamaged coating degraded in the measurement at around 450 °C, the irradiated coatings kept high permeation reduction performance after the measurement at 600 °C. The total electrical conductivities of the irradiated coatings were up to two orders of magnitude higher than those of the undamaged one below 400 °C and then increase linearly with inverse temperature. The dominant influence on the electrical conductivity was irradiation defects at low temperatures and the inherent conduction performance of the coating at high temperatures. Our results show that electrochemical impedance measurements are useful even for submicron-thick ceramic thin coatings and confirm the irradiation effects on electrical conductivity, especially in the low-temperature range.

The synergy of heavy-ion irradiation and lithium-lead corrosion on deuterium permeation behavior of ceramic coating

Functional ceramic coatings have been investigated for several decades to mitigate tritium permeation through structural materials in a fusion reactor blanket. For the establishment of a liquid blanket system, the coatings require not only tritium permeation reduction but also the tolerance to irradiation damage induced by neutrons and corrosion by liquid tritium breeders. In this study, deuterium permeation measurements under exposure to liquid lithium–lead were performed for a heavy-ion-irradiated zirconium oxide coating sample to elucidate the synergy of irradiation and corrosion on hydrogen isotope permeation. The irradiated coating decreased the deuterium permeation flux under lithium–lead exposure by more than two orders of magnitude in comparison with the unirradiated one. Each activation energy of permeation and diffusion of the coating sample was larger than that of the unirradiated one at around 450 °C and decreased to the level of the unirradiated one at 600 °C. The results indicated that the voids formed by ion irradiation aggregated in grain boundaries of the coating, resulting in an increase in the energy barrier of diffusion at low temperatures and then a decrease due to the defect recovery at high temperatures. Besides, a corrosion product layer formed on the coating during lithium–lead exposure increased the energy barrier of solution. The synergy of irradiation and corrosion on permeation was developed at lower temperatures before the defect recovery.

Corrosion of reduced activation ferritic-martensitic steel CLF-1 by Li2TiO3 in ambient air

In a solid tritium breeding blanket, tritium breeder Li2TiO3 is in contact with reduced activation ferritic martensitic steel at high temperatures for years and accordingly form a corrosion layer on the blanket structural steel. The effects of the corrosion layer on the deuterium permeability of RAFM steel CLF-1 were thus investigated. X-ray diffraction, secondary ion mass spectroscopy and high-resolution transmission electron microscopy proved the formation of a double layered corrosion products with a thickness of ∼200nm . A localized LiCrO2 (003)/LiFeO2 (003) interface between the outer layer LiFeO2 and the inner layer LiCrO2 was observed. With the increase of corrosion periods (120∼360 h), there is a first deuterium permeability increase due to cracking and an amorphization process occurred at the interface between the corrosion layer and the substrate. The CLF-1 steel corroded for 720 hours performed a lowest deuterium permeation flux as the amorphous oxides have been entirely crystallized. A localized corrosion mechanism coexisting with uniform corrosion was proposed to explain the changing deuterium permeability of the CLF-1 steel corroded by Li2TiO3 in 1 atm ambient air atmosphere. Our study provides a novel thought on reducing the tritium permeability of the RAFM steel.

Submicron-thick yttria-stabilized zirconia coating as an advanced tritium permeation barrier

Tritium permeation through structural materials is one of the critical issues in a fusion reactor from the viewpoints of an efficient fuel cycle and radiological safety. Ceramic coatings have been studied as tritium permeation barriers (TPBs) and shown sufficient reduction of hydrogen isotope permeation. In high thermal efficiency liquid blanket concepts, however, not only tritium permeation but also corrosion of the structural materials by liquid tritium breeders such as lithium–lead (Li–Pb) is a serious concern. This study focuses on the fabrication of two kinds of yttria-stabilized zirconia (YSZ) coatings by metal organic decomposition and characterization through several tests such as deuterium permeation and static Li–Pb exposure. The 4 mol%-Y2O3-containing YSZ coating of less than 100 nm in thickness showed three orders of magnitude lower deuterium permeation flux than uncoated substrate after crystallization and grain growth, and the high permeation reduction performance maintained through the thermal cycle tests. The 10 mol%-Y2O3-containing YSZ coating sample showed a high permeation flux due to the defects formed during the permeation measurement. Both coatings showed compatibility with Li–Pb. A phase transformation was confirmed in the 4 mol%-Y2O3-containing YSZ coating after bending tests, suggesting that the coating sample achieved a self-repairing property. These results indicate that the 4 mol%-Y2O3-containing YSZ coating would apply to the TPB.

Effect of thermal cycles on structure and deuterium permeation of Al2O3 coating prepared by MOD method

Abstract The effect of thermal cycles on the microstructure and deuterium permeation of the Al2O3 coatings prepared by the MOD method was investigated. An as-deposited Al2O3 coating showed a uniform, smooth and dense surface morphology and was composed of γ-Al2O3 and α-Al2O3 phases. After 550 °C thermal cycles, all the Al2O3 coatings exhibited good phase stability. The Al2O3 coating remained intact and dense after 100 thermal cycles, while obvious cracks appeared on the coating surface after 150 thermal cycles. Furthermore, a deuterium permeation test of the as-deposited and thermally cycled Al2O3 coatings was carried out. The deuterium permeation flux of the Al2O3 coating increased with increasing the number of thermal cycles. The Al2O3 coatings with fewer than 100 thermal cycles remained dense and had a smooth surface morphology. However, several cracks appeared on the surface of the coating after 100 thermal cycles. In particular, delamination of the coating occurred after 150 thermal cycles. Disappearance of the (400) and (441) diffraction peaks of the γ-Al2O3 was observed after the deuterium permeation tests. The microscopic mechanism of the influence of thermal cycles on the microstructure and deuterium permeation of the Al2O3 coatings was analyzed.

Hydrogen isotope permeability of reduced activation ferritic/martensitic steel CLF-1 corroded by Li4SiO4

In a solid tritium breeding blanket, Li4SiO4 is in contact with reduced activation ferritic/martensitic (RAFM) steel at high temperatures for years and forms a corrosion layer. The effects of the corrosion layer on the hydrogen isotope permeability of a RAFM steel CLF-1 were thus investigated. X-ray diffraction, secondary ion mass spectroscopy and spherical aberration corrected transmission electron microscopy demonstrated the formation of a three-layered corrosion product, comprising a middle layer of LiFeO2 and an inner layer of LiCrO2. Li4SiO4 powder with the (104) crystal plane orientation was adsorbed on the outermost surface of the CLF-1, forming a nanoscale layer with a thickness of ∼150 nm. Deuterium permeation tests show that the deuterium permeability of the corroded samples was two orders of magnitude higher than that of the blank substrate that was pre-heated for 30 days, but one order of magnitude lower than that of the blank substrate that was not preheated. The CLF-1 corroded for 10 days exhibited the highest deuterium permeation flux. There was a decrease in the deuterium permeability of the steel that corroded for 15 and 30 days; thus, there was a decrease in the permeability with an increase in the corrosion period. By the weighting method and TEM analysis, a cracking and reoxidation process was proposed to explain the decreasing deuterium permeability of CLF-1 during corrosion by Li4SiO4. Our study provides a promising approach for preventing tritium permeation.

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.

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.

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.

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.

Deuterium permeation behavior and its iron-ion irradiation effect in yttrium oxide coating deposited by magnetron sputtering

Tritium permeation through structural materials is a critical issue in fusion reactors from the viewpoints of sufficient fuel balance and radiological hazard. Ceramic coatings have been investigated as tritium permeation barrier for several decades; however, irradiation effects of the coatings on permeation are not elucidated. In this work, yttrium oxide coatings were fabricated on reduced activation ferritic/martensitic steels by radio frequency magnetron sputtering, and their microstructures and deuterium permeation behaviors were investigated before and after iron-ion irradiation at different temperatures. An as-deposited coating had a columnar structure and transformed into a granular one after annealing. An amorphous layer formed near the coating-substrate interface of irradiated coatings, and its thickness became thinner with increasing irradiation temperature. Voids of approximately 20 nm in diameter also formed in the irradiated coatings. Deuterium permeation flux of the sample irradiated to 1 dpa at room temperature was the lowest among the unirradiated and irradiated samples, and a permeation reduction factor indicated up to 390. The amorphous layer disappeared after deuterium permeation measurements due to damage recovery, while the voids remained and aggregated. The irradiation damage would accelerate nucleation of the crystal, resulting in a decrease of the permeation flux.

Deuterium permeation through metals under γ-ray irradiation

Tritium handling in fusion reactors is important for economical fuel cycles and radiological safety; however, the extremely limited number of studies on tritium permeation through structural materials under irradiation conditions has been reported. In this study, γ-ray irradiation effect on tritium permeation has been investigated using three kinds of metals with different permeation properties including palladium, platinum, and austenitic stainless steel. An increase of deuterium signal on the quadrupole mass spectrometer during irradiation consisted of an increase of deuterium permeation flux and an electrical noise, and both were separately detected. The increase rate of permeation flux for all materials became lower as the test temperature increased. Dose rate dependence of the increase rate was confirmed. Oxidation of the austenitic stainless steel indicates a decrease of not only the deuterium permeation flux but also the irradiation effect.

Influence of sub-surface damage evolution on low-energy-plasma-driven deuterium permeation through tungsten

Low-energy-plasma-driven deuterium permeation through tungsten at 300 K and 450 K has been investigated. Microstructural analysis by scanning electron microscopy, assisted by focused ion beam, revealed sub-surface damage evolution only at 300 K. This damage evolution was correlated with a significant evolution of the deuterium amount retained below the plasma-exposed surface. Although both of these phenomena were observed for 300 K exposure temperature only, the deuterium permeation flux at both exposure temperatures was indistinguishable within the experimental uncertainty. The permeation flux was used to estimate the maximum ratio of solute-deuterium to tungsten atoms during deuterium-plasma exposure at both temperatures and thus in the presence and absence of damage evolution. Diffusion-trapping simulations revealed the proximity of damage evolution to the implantation surface as the reason for an only insignificant decrease of the permeation flux.

Deuterium permeation behavior of tritium permeation barrier coating containing carbide nanoparticles

Y2O3 coatings containing Cr3C2 nanoparticles have been prepared on reduced activation ferritic/martensitic steel F82H substrates by metal organic decomposition with dip-coating technique, and their deuterium permeation behaviors have been investigated. The surface condition of the samples varied with pre-treatment process: fabrication of Y2O3 coatings without the Cr3C2 nanoparticles or surface oxidation of F82H. In the coating without pre-treatment, peeling of agglomerated nanoparticles and oxidation of the substrate at the peeled regions were observed. Pores were also observed in the coatings with pre-treatment; however, iron oxide was not formed. The deuterium permeation flux of the coating fabricated without pre-treatment was lower than that of uncoated F82H substrate by a factor of 100 even after crystallization at 700°C. In the case of the sample with pre-treatment, the permeation flux was by a factor of 100 lower than that of uncoated substrate before crystallization, and the factor increased to approximately 1000 after crystallization. Dispersion of the nanoparticles and securement of surface coverage of the coating are key factors to establish high-performance tritium permeation barrier.

Crystallization and deuterium permeation behaviors of yttrium oxide coating prepared by metal organic decomposition

Yttrium oxide coatings were fabricated on reduced activation ferritic/martensitic steels by metal organic decomposition with a dip-coating technique, and their deuterium permeation behaviors were investigated. The microstructure of the coatings varied with heat-treatment temperature: amorphous at 670ºC (amorphous coating) and crystallized at 700ºC (crystallized coating). Deuterium permeation flux of the amorphous coating was lower than the uncoated steel by a factor of 5 at 500ºC, while that of the crystallized coating was lower by a factor of around 100 at 400‒550ºC. The permeation fluxes of both coatings were drastically decreased during the measurements at higher temperatures by a factor of up to 790 for the amorphous coating and 1000 for the crystallized one, indicating a microstructure modification occurred by an effect of test temperature with hydrogen flux. Temperature dependence of deuterium diffusivity in the coatings suggests that the decrease of the permeation flux has been derived from a decrease of the diffusivity. Characteristic permeation behaviors were observed with different annealing conditions; however, they can be interpreted using the permeation mechanism clarified in the previous erbium oxide coating studies.

Deuterium permeation through erbium oxide coatings on RAFM steels by a dip-coating technique

A tritium permeation barrier is a promising solution for the problems of tritium loss and radiological safety in fusion blanket systems. In recent years, erbium oxide coatings have shown remarkable permeation reduction factors. One of the remaining issues for the coatings is the establishment of plant-scale fabrication. In this study, erbium oxide thin films have been fabricated by a dip-coating technique, which has the potential to coat a complex-shaped substrate, and deuterium permeation behavior in the coatings has been examined. Crack-free coatings were formed on a reduced activation ferritic/martensitic steel F82H substrate by use of a withdrawal speed of 1.0–1.4mms−1 and a heat-treatment process in hydrogen with moisture. In deuterium permeation experiments, a 0.2-μm-thick coating on both sides of the substrate showed a reduction factor of 600–700 in comparison with a F82H substrate below 873K; however, the coating degraded at above 923K because of crack formation. A double-coated sample indicated a reduction factor of up to 2000 and did not degrade at up to 923K. The driving pressure dependence of the deuterium permeation flux indicated that the permeation tended to be limited by surface reactions at low temperatures. Optimization of the number of layers has the possibility to reduce degradation at high temperatures while maintaining high permeation reduction factors.