Deuterium Trapping Research Articles

Influence of neon seeding on the deuterium retention and surface modification of ITER-like forged tungsten

In order to investigate the effect of neon seeding on deuterium retention and surface modification of ITER-like forged tungsten with grains elongated perpendicular to the surface, pure and neon-seeded deuterium plasma exposures were performed in the linear plasma device PSI-2. The ion percentage of neon in the mixed plasma was around 10%. The sample temperature and deuterium ion fluence were kept at 450 K and 1 × 1026 m−2, respectively. The incident ion energy was 40 eV, just reaching the tungsten sputtering threshold for neon. Surface observations show that neon seeding leads to pronounced cracking and erosion of blister caps and a significant reduction of small blisters (<0.8 μm). This is possibly attributed to surface sputtering and the inhibitory effect of neon-induced defects on blister nucleation by hindering dislocation movements. On the other hand, neon seeding increases the total deuterium retention by ∼70% according to the thermal desorption spectroscopy (TDS) measurements. A low-temperature desorption peak (∼660 K) which should be mainly ascribed to deuterium de-trapping from dislocations is observed to be broadened and shifts towards higher temperature in the case of neon seeding, suggesting enhanced inward diffusion and trapping of deuterium. An additional deuterium release peak appears at a higher temperature (∼803 K), indicating the creation of new deuterium-traps induced by neon. A comparison of the results of nuclear reaction analysis and TDS reveals that neon seeding not only increases deuterium retention in the surface region (<7.2 μm) but also in the bulk (>7.2 μm). We ascribe the enhanced deuterium retention to the increased deuterium-traps in the top-surface induced by Ne irradiation and the vertical grain boundary configuration of the forged W promoting the inward diffusion of deuterium.

Characterisation of deuterium distributions in corroded zirconium alloys using high-resolution SIMS imaging

Hydrogen diffusion through the oxide grown on Zr alloys by aqueous corrosion processes plays a critical role in determining the rate of hydrogen pickup (HPU) which can result in embrittlement of fuel cladding and limit the burnup of the nuclear fuel it encapsulates. Mapping the hydrogen/deuterium distributions in these oxide layers, especially in the barrier layer close to the metal/oxide interface, is a powerful way to understand the mechanism of both oxidation and hydrogen pickup. Here we have characterised by high-resolution SIMS analysis the deuterium distribution in oxide layers on a series of Zr alloys, including autoclave-oxidised Zircaloy-4, Zr-1Nb and Zr-2.5Nb alloys, and in-flux and out-of-flux corroded Zr-2.5Nb samples. Pre-transition Zircaloy-4 samples show a high deuterium trapping ratio in the oxide and a higher diffusion coefficient than in oxides on the Nb-containing samples. Neutron irradiation increases the deuterium diffusion coefficient, the deuterium concentration in the oxide and the pickup fraction in Zr-2.5 Nb samples. Comparative NanoSIMS and EDX/SEM analysis demonstrates that the deuterium is not preferentially trapped at second phase particles in the oxides on any of the alloys studied, but there is direct evidence for trapping at the surfaces of small oxide cracks especially in Zircaloy-4 samples. The high resolution mapping of these hot-spots in 3D can provide unique information on the mechanisms of hydrogen uptake, and suggests that the development of interconnected porosity in the oxide may be the critical rate-determining mechanism that controls HPU in the aqueous corrosion of zirconium alloys in water-cooled reactors.

THE INFLUENCE OF 18Cr10NiTi AND ODS 18Cr10NiTi AUSTENITIC STAINLESS STEELS MICROSTRUCTURE ON THE DEUTERIUM DESORPTION

The thermal desorption spectra of deuterium from 18Cr10NiTi and ODS 18Cr10NiTi steel specimens irradiated with 10 keV D2+ ions were examined. The influence of radiation damage on microstructure and accumulation of deuterium implanted in steels at room temperature and after annealing have been studied. Thermal desorption spectrum (TDS) from a specimen of ODS 18Cr10NiTi steel exhibits deuterium release over a wide temperature range with two well-defined maxima at ~ 420 and ~ 970 K. Two types of precipitates – oxides (Y-Ti-O) and carbides TiC are considered to explain the mechanism of the deuterium trapping to high annealing temperatures.

Hydrogen-isotope transport in Ti-added reduced activation ferritic/martensitic steel

Abstract The Korea Institute of Materials Science has been developing a new reduced activation ferritic/martensitic (RAFM) steel, named Ti-RAFM, in which Ti replaces Ta. It is characterized by higher mechanical strength than RAFM steel with Ta without loss of impact properties. The permeation and trapping of hydrogen, deuterium, and tritium in Ti-RAFM were investigated at temperatures of 160–600 °C. The properties of hydrogen and deuterium were determined using the continuous-flow method whereas that of tritium was calculated using a model associated with quantum harmonic approximation. This study reports the first complete datasets of the permeability of hydrogen, deuterium, and tritium in Ti-RAFM and the corresponding datasets for the diffusivity and solubility including the trapping energy and trap density, which were determined from the trapping phenomena observed at low temperatures of 160–300 °C. The ratios of hydrogen, deuterium, and tritium for the permeability, diffusivity, and solubility were also estimated. Furthermore, our results for Ti-RAFM were compared with the results for other RAFMs.

Characterisation of Deuterium Distributions in Corroded Zirconium Alloys Using High-Resolution SIMS

Hydrogen diffusion through the oxide grown on Zr alloys by aqueous corrosion processes plays a critical role in determining the rate of hydrogen pickup which can result in embrittlement of fuel cladding and limit the burnup of the nuclear fuel it encapsulates. Mapping the hydrogen/deuterium distributions in these oxide layers, especially in the barrier layer close to the metal/oxide interface, is a powerful way to understand the mechanism of both oxidation and hydrogen pickup. Here we have characterised by high-resolution SIMS analysis the deuterium distribution in oxide layers on a series of Zr alloys, including autoclave-oxidised Zircaloy-4, Zr-1Nb and Zr-2.5Nb alloys, and in-flux and out-of-flux corroded Zr-2.5Nb samples. Pre-transition Zircaloy-4 samples show a high deuterium trapping ratio in the oxide and a higher diffusion coefficient than in oxides on the Nb-containing samples. Neutron irradiation increases the deuterium diffusion coefficient, the deuterium concentration in the oxide and the pickup fraction in Zr-2.5 Nb samples. Comparative NanoSIMS and EDX/SEM analysis demonstrates that the deuterium is not preferentially trapped at SPPs in the oxides on any of the alloys studied, but there is direct evidence for trapping at the surfaces of small oxide cracks especially in Zircaloy-4 samples. The high resolution mapping of these hot-spots in 3D can provide unique information on the mechanisms of hydrogen uptake, and suggests that the development of interconnected porosity in the oxide may be the critical rate-determining mechanism that controls HPU in the aqueous corrosion of zirconium alloys in water-cooled reactors.

Trapping and release of helium and deuterium in recrystallized and heavily deformed tungsten after plasma exposure

Interaction of tungsten surface with plasma beam has tremendous importance for development of materials for fusion applications. Trapping and release of Helium (He) and Deuterium (D) in tungsten exposed to high flux plasma with varying He and D content are studied here. Recrystallized and plastically deformed tungsten samples were used to clarify the impact of the material microstructure on trapping and release of plasma components. Thermal desorption spectroscopy measurements were performed to reveal the release stages and quantify the integral desorption of both types of molecules. Comparison of reference and plastically deformed samples was used to clarify the impact of plastic deformation (expressed in the high dislocation density and dislocation networks) on the trapping and release processes. It has been demonstrated that in the mixed beam exposures, the integral He release weakly depends on the He/D ratio, but suddenly grows as the fraction of He/D increases from 80/20 to 100/0. The integral release of D is remarkably enhanced by He seeding in both reference and plastically deformed samples. It is concluded that under the mixed beam exposure conditions, the D release is primary controlled by the He seeding and not by the deformation-induced microstructure.

High-yield cellulose hydrolysis by HCl vapor: co-crystallization, deuterium accessibility and high-temperature thermal stability

Hydrochloric acid hydrolysis in its gas form was used to produce cellulose nanoparticles from flax shives with a very high yield (> 90%). The efficiency of the transformation was examined by gravimetry, atomic force microscopy and transmission electron microscopy. A novel purpose-built anisotropic line-broadening X-ray diffraction model was used. This XRD method uses a parametric shape in order to address the issue of strongly broadened and overlapping Bragg rays that are characteristic of nano-sized crystallites. This method demonstrated the remarkable stability of the crystallite shapes during hydrolysis and its sensibility was sufficient to detect a minor co-crystallization along the hydrophilic faces. The presence of amorphous material strictosensu in the form of individual and randomly oriented chains was not necessary to describe the diffractograms accurately. Thermal FTIR with isotopic exchange was also performed using deuterium oxide to characterize the accessibility of the materials between 20 and 260 °C. Further, back-exchange experiments were performed in order to quantify the hysteretic amount of deuterium that was trapped by microstructural reorganization. These experiments showed that hydrolysis cancelled any form of deuterium trapping (water-induced co-crystallization). For the first time, thermal FTIR demonstrated that isotopic labelling of cellulose sources can produce false positives when conducted at room temperature and thermal FTIR can unambiguously distinguish between labelled cellulose groups and free deuterium oxide, which is paramount when measuring the higher accessibility of the nanocelluloses. It was also demonstrated that the high-temperature hydrogen bond reorganization and thermal degradation of the cellulose chains strongly depend on the hydrolysis and on the microstructure of the substrate.

A setup for study of co-deposited films

A setup for investigation of thermal desorption spectra of gases accumulated in thin films deposited by plasma sputtering of solid targets is described. Deposition and thermal desorption spectroscopy (TDS) are performed in two different vacuum chambers separated by a gate valve with the sample transferred between the chambers in-vacuo. The temperature of the substrate for deposited films can be varied in the range of 300–800 K; and the deposition rate is controlled by a quartz microbalance. Thermal desorption of co-deposited gases is analyzed by a quadrupole mass spectrometer. Sputtering rate and evaporation of the film during TDS are measured by quartz microbalances. Three experiments are described 1) trapping of deuterium by the growing chemically active Li film with subsequent decomposition and evaporation of the film, 2) temperature dependent deuterium trapping in the growing W film resulting in trapping with several binding energies, and 3) chemical interaction of D-Li layer with water vapor leading to isotopic H-D exchange and chemical transformation of the deposited film.

2,3,3,3‐Tetrafluoropropene (HFO‐1234yf) as a CF3‐Building Block: Synthesis of Enol Ethers and Vinyl Sulfides

2,3,3,3‐Tetrafluoropropene (HFO‐1234yf) is an inexpensive and readily available fluorinated building block, owing to its growing use as a low global warming potential 4th generation refrigerant, but there have so far been few reported uses of this fluoroalkene in organic synthesis. Herein, we report our investigations into nucleophilic substitution reactions of HFO‐1234yf with alkoxide and thiolate derivatives. The regiochemistry of these transformations varies with conditions and we propose these reactions proceed through addition–elimination with reversible formation of a carbanion intermediate. The regioselectivity is dictated by hard/soft nucleophile/electrophile control. This is supported by deuterium trapping of the proposed reactive intermediate. The effect of solvent and base choice was examined and the substrate scope for the synthesis of α‐trifluoromethyl enol ethers was expanded.

The effects of irradiation and high temperature on chemical states in Li2TiO3

In the future D-T fusion reactor, tritium will be bred mainly by the reaction of 6Li (n, α) T, as well as 7Li (n, n’ α) T in tritium breeding materials. Solid breeding materials will experience harsh conditions under both irradiations by energetic particles (neutron, tritium, helium and self-particles) and high temperature. The interactions of irradiations and high temperature on lithium ceramics will influence tritium breeding ratio (TBR). The changes of chemical states and its effects on release behavior of hydrogen isotopes in deuterium-irradiated Li2TiO3 and deuterium-exposed Li2TiO3 at high temperature have been investigated. The peak of O-1s shifted to higher binding energy by both irradiation and deuterium exposure, indicating that O-D bonds formed. The amount of O-D bonds enhanced as increase of irradiation fluence and exposure temperature. The main deuterium atoms were trapped by defects for irradiated samples. Annihilation of E-centers was thought to trigger the release of hydrogen isotopes. O-D bonds were the main deuterium trapping sites in deuterium-exposed Li2TiO3. Deuterium recovered by detrapping O-D bonds would require higher temperature. Both deuterium-irradiation and deuterium-exposure at high temperature could result in the change of chemical states in Li2TiO3. The changes in chemical states had effects on deuterium release. It illustrates that tritium breeding materials in fusion reactor will be modified by both irradiation and high temperature and could result in lower tritium recovery.

Deuterium trapping by deformation-induced defects in tungsten

The influence of defects induced by plastic deformation of tungsten (W) on deuterium (D) retention has been studied. Recrystallized W samples were subjected to tensile deformations at temperatures of 573 K and 873 K to strains in the range of 3%–38%. The dislocation density measured by transmission electron microscopy increased by about 40 times after deformation to the highest strain. The introduced defects were decorated with D by exposure to a low-flux D plasma at sample temperatures of 370 K and 450 K. D retention in the samples was studied using nuclear reaction analysis and thermal desorption spectroscopy. The trapped D concentrations after the plasma exposures were low (up to a few times 10−4 at. fr.) and increased more slowly with strain than the dislocation density. Small vacancy-like defects and large vacancy clusters were detected in the samples by positron annihilation lifetime spectroscopy. Their concentrations also increased with strain more weakly than the dislocation density. It was concluded that these defects governed the D retention under plasma exposure at 450 K, while dislocations gave only a small contribution. It was also found that deformation already to the lowest strains significantly facilitates the formation of blister-like structures under D plasma exposure at 370 K. The defects associated with blister-like structures presumably gave a substantial contribution to D retention at 370 K.

Evaluation of tungsten as divertor plasma-facing material: results from ion irradiation experiments and computer simulations

The effect of the primary knock-on atom (PKA) spectrum in radiation damage and the subsequent defect structure formation and their impact in deuterium (D) trapping has been investigated using computer simulations and surrogate ion irradiation experiments. The neutron spectrum for an ‘ITER-like’ divertor shape and parameters has been generated using ATTILA and SPECTER codes to identify the relevant PKA energies. It has been observed that 10 MeV boron (B) produces a PKA spectrum similar to that obtained from a reactor-like neutron spectrum. Experiments have been carried out with ions of gold (Au), B, helium (He) and D with energies ranging from 0.1 MeV–80 MeV for a fluence range of ions m−2– ions m−2, and distinctly different PKA spectra have been produced. While 80 MeV Au ions produced dense and small clusters of interstitial defects (<10 nm), B produced large dislocation loops up to 60 nm in size. At room temperature, the imprint of the cascade is well captured by the vacancies due to their low mobility, and the vacancy defects observed in Au and B irradiation showed significant differences. Molecular dynamics simulations show that at PKA energies exceeding 150 keV, the fragmentation of the cascades takes place, which tends to limit the size of individual defects in the case of 80 MeV Au irradiation. A mechanism based on the competitive capture of mobile interstitials has been proposed to explain the observed large dislocation loops as well as dislocation lines in different irradiation experiments.

Investigation of deuterium trapping and release in the JET divertor during the third ILW campaign using TDS

Selected set of samples from JET ITER-Like Wall (JET-ILW) divertor tiles exposed in 2015-2016 has been analysed using Thermal Desorption Spectrometry (TDS). The deuterium (D) amounts obtained with ...

Investigation of deuterium trapping and release in the JET ITER-like wall divertor using TDS and TMAP

Selected set of samples from JET ITER-Like Wall (JET-ILW) divertor tiles exposed both in 2013-2014 and 2011-2014 has been analysed using Thermal Desorption Spectrometry (TDS). The deuterium (D) amo ...

Temperature dependence of hydrogen co-deposition with metals

The deuterium retention in aluminum and molybdenum films co-deposited in magnetron discharge has been measured in a wide range of substrate temperatures (from RT to 800 K) by means of thermal desorption spectroscopy. A multi-step temperature dependence was observed, which was compared with the diffusion based model and previous experimental data for tungsten films. The key role of lattice defects in deuterium trapping was demonstrated. The highest D retention among the investigated materials was observed in W films, which have the lowest H solubility, but the highest binding energies of hydrogen with defects. The detrapping energies and concentrations of defects in the films were estimated on the base of the model, and the energies are consistent with the data for bulk materials.

Deuterium retention in advanced steels for fusion reactor structural application

Reduced activation ferritic-martensitic (RAFM) steels, castable nanostructured alloys (CNA), and oxide-dispersion-strengthened (ODS) steels have been developed for the fusion reactor structural application with improved mechanical properties and radiation resistance. However, the hydrogen isotope retention in these steels is not well understood. In this study, 10 keV D2 implantation was performed on six steels, together with pure iron and T91 as references, at room temperature. Subsequent thermal desorption spectroscopy (TDS) measurements were carried out to investigate the deuterium retention. Possible deuterium trapping sites in the studied materials were discussed in coordination with available microstructural information. The results indicated that ODS-steels have the largest deuterium retention, which is almost one order of magnitude higher than that of pure iron, ∼6 times of RAFM, and 2–4 times of CNA steels. The difference in nanoparticles and grain/lath boundaries are primarily responsible for the different deuterium retention, while other trapping sites (e.g., vacancy clusters, dislocations, etc.) are present. Deuterium retention increases with increasing sink strength of the studied materials, although they are not linear correlated.

Hydrogen Isotope Trapping in Tungsten During Cyclic Irradiation by Deuterium and Hydrogen Ions in Oxygen-containing Atmosphere

An investigation on mechanisms of hydrogen and deuterium trapping in tungsten during irradiation by hydrogen ion plasma with oxygen impurity using the methods of thermal desorption spectrometry (TDS) and secondary ion mass spectrometry (SIMS) is presented in this paper. It was shown that almost 40% of trapped particles were retained in the surface oxide layer after first implantation of deuterium. Subsequent irradiation by hydrogen plasma with oxygen impurity lead to the increase of oxygen concentration and hydrogen trapping in the oxide layer and tungsten bulk. In the next cycle, which started with deuterium implantation, oxygen concentration in the oxide layer decreased and some hydrogen was removed from tungsten. Then an increase of hydrogen and oxygen concentration in the sample repeated during irradiation with ions of (H2 + 1 at. % O2) plasma. The same sequence of processes was observed during subsequent irradiation cycles.

Identification of BeO and BeOxDy in melted zones of the JET Be limiter tiles: Raman study using comparison with laboratory samples

Beryllium oxide (BeO) and deuteroxide (BeOxDy) have been found on the melted zone of a beryllium tile extracted from the upper dump plate of JET-ILW (2011–2012 campaign). Results have been obtained using Raman microscopy, which is sensitive to both the chemical bond and crystal structure, with a micrometric lateral resolution. BeO is found with a wurtzite crystal structure. BeOxDy is found as three different types which are not the β-phase but behaves as molecular species like Be(OD)2, O(Be-D)2 and DBeOD. The presence of a small amount of trapped D2O is also suspected. Our results therefore strongly suggest that D trapping occurs after melting through the formation of deuteroxides. The temperature increase favors the formation of crystal BeO which favors deuterium trapping through OD bonding.

Hydrogen isotope trapping and retention in graphite and boron carbide under consecutive irradiation by deuterium and hydrogen plasma

The results of study on hydrogen and deuterium trapping and retention in MPG-8 grade graphite and boron carbide coating under consecutive irradiation by deuterium and hydrogen plasma in varying hydrogen irradiation conditions are presented in this paper. It is shown that deuterium content decreases both in graphite and boron carbide under irradiation by hydrogen plasma. It is also shown that the main mechanism of deuterium removal is sputtering for graphite, and isotope exchange for boron carbide.

Ionizing radiation effects on the thermal stability of deuterium trapping in reaction bonded SiC

SiC materials are prime candidates for flow channel inserts in the dual coolant lithium lead blanket concept. Flow channel inserts made of SiC will be exposed to tritium from the Li transmutation, as well as to neutron and gamma radiation. Hence a critical issue for future fusion devices is to clarify hydrogen isotope behaviour in SiC under such conditions. The objective of the work presented here is to study the effect of ionizing radiation on the deuterium trapping in Reaction Bonded SiC in similar conditions as reactor materials. This effect is evaluated by studying the influence of ionizing radiation on deuterium trapping (for both implanted and loaded SiC samples). Moreover, it is investigated how deuterium trapping may be modified by displacement damage. The ionizing radiation effect on absorption has also been evaluated for samples pre-damaged by self-ion irradiation. The irradiation and implantation experiment have been carried out at the CMAM-UAM accelerator, and the Danfysik implanter and 2 MeV Van de Graaff electron accelerator at CIEMAT. Samples are analysed by thermal desorption spectroscopy and secondary ion mass spectrometry (SIMS) to clarify the mechanisms involved in the trapping processes, depending on the different experimental conditions. The results for the deuterium loaded samples indicate that absorption is increased by ionizing radiation. When samples are pre-damaged by C+4 ions, deuterium absorption is increased in the form of Si-D according to SIMS results. Furthermore, the effect of ionizing radiation after deuterium implantation is an enhancement of the deuterium released from SiC. The deuterium release observed in this case is forming hydrocarbons during irradiations.