Relevant parameters for trapping of Hydrogen Isotopes (HIs) in polycrystalline tungsten are determined with the MHIMS code (Migration of Hydrogen Isotopes in MaterialS) which is used to reproduce ...Thermal Desorption Spectrometry experiments. Three types of traps are found: two intrinsic traps (detrapping energy of 0.87 eV and 1.00 eV) and one extrinsic trap created by ion irradiation (detrapping energy of 1.50 eV). Then MHIMS is used to simulate HIs retention at different fluences and different implantation temperatures. Simulation results agree well with experimental data. It is shown that at 300 K the retention is limited by diffusion in the bulk. For implantation temperatures above 500 K, the retention is limited by trap creation processes. Above 600 K, the retention drops by two orders of magnitude as compared to the retention at 300 K. With the determined detrapping energies, HIs outgassing at room temperature is predicted. After ions implantation at 300 K, 45% of the initial retention is lost to vacuum in 300 000 s while during this time the remaining trapped HIs diffuse twice as deep into the bulk.
•Code development to solve numerically the model equations of diffusion and trapping of hydrogen in metals.•Parametrization of the model trapping parameters (detrapping energies and density): fitting of experimental TDS spectrum.•Confrontation model/experiment: evolution of retention with fluence and implantation temperature.•Investigation of period of rest between implantation and TDS on retention and depth profile.
Feasibility of in situ LIBS remote measurements with the plasma facing components (PFCs) from the European tokamaks (TORE SUPRA, CEA Cadarache, France and TEXTOR, Julich, Germany) has been studied in ...laboratory using Q-switched nanosecond Nd–YAG lasers. LIBS particular properties and optimal parameters were determined for in-depth PFCs characterisation. The LIBS method was in situ tested on the Joint European Torus (JET) in the UK with the EDGE LIDAR Laser System (Ruby laser, 3J, 690nm wavelength, 300ps pulse duration, intensity up to 70GW/cm2). Several analytical spectral lines of H, CII, CrI, and BeII in plasma were observed and identified in 400–600nm spectral range with the optimised LIBS and detection system. The LIBS in-depth cartography is in agreement with the surface properties of the tile under analysis, thus confirming feasibility of in situ LIBS. Further LIBS technique improvements required to provide tritium concentration measurements more accurately are discussed.
In the framework of the TRANSAT project, started in 2017 (TRANSversal Actions for Tritium supported within the H2020 Euratom program), the ability to measure and to assess the tritium inventory and ...migration within different kinds of reactors or processes is one major challenge to control the potential releases and personal dosimetry in nominal operating conditions.
A benchmarking activity between two calculation tools developed either for the fusion machines (EcosimPro developed between CIEMAT and EAI) or for the fission reactors (KUTIM developed at CEA), was initiated to improve the level of confidence in the tritium and hydrogen balances estimated by such codes in complex systems.
An application to a conceptual fission reactor based on the technology of Sodium Fast Reactors was carried out on the base of a shared data set used for the design characteristics of circuits and components as well as for physico-chemical properties of liquid sodium, of wall materials and of operating conditions. The modeling of specific components or physical equilibriums involved in sodium cooled reactors was adapted and implemented in EcosimPro libraries. In particular the major recovery of tritium and hydrogen impurities in purification systems (cold traps) is evaluated as well as the dissolution equilibrium of both hydrogen isotopes at the primary sodium surface between the liquid metal and the gas plenum.
Calculations results with both codes are presented and compared in terms of tritium activities and hydrogen concentrations in each circuit of the reactor, but also in terms of transfer fluxes and releases. In addition, the distribution of the various transfer contributions (between primary, secondary and tertiary circuits) is analyzed. Comparisons between both codes results associated with sensitivity studies on the influence of main parameters (such as tritium and hydrogen source terms, temperature profiles) are also used to propose perspectives of modeling improvements.
Tritium retention in plasma facing materials such as tungsten is a major concern for future fusion reactors. During ITER operating mode, the reactor could generate tritiated tungsten dust-like ...particles which need to be characterized in terms of amount of trapped tritium, tritium source and radiotoxicity. This study is focused on the preparation and characterization of tungsten particles and on a comparative analysis of tritium absorption/desorption kinetics in these particles and in massive samples. An original gas phase thermal charging procedure was used successfully for tritium incorporation in tungsten powders and massive samples. Much larger tritium amounts are incorporated in W particles than in massive samples indicating important surface effects on tritium absorption, desorption and trapping in W. Tritium desorption from particles occurred at different temperatures related with different interactions on the particles surface and in the bulk; the tritium behavior in massive samples was also shown to depend on the metal microstructure. According to these experimental results tritium absorption/desorption in W particles may have important implications on tritium management in ITER reactor.
•An original technique was used for tritium charging of tungsten particles and massive samples.•When compared to massive samples, very large tritium amounts are incorporated in W particles.•Surface effects are predominant on tritium absorption/retention in W particles.•Tritium absorption and trapping depend on oxide films on W particles and on defects in massive samples.•Absorption/retention of 3H in W may affect 3H management and radiotoxicity of ITER-like W particles.
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•Synthesis of tungsten nanoparticles with concave hexapod and cube-octahedral shapes is reported.•The hexapod nanoparticles present a dendritic growth.•The cube-octahedral ...nanoparticles present a single crystal structure.•Enhanced stability of the β-W phase in hexapod nanoparticles is reported.
We report the synthesis of tungsten nanoparticles with two distinct shapes, concave hexapods and faceted cube-octahedral nanocrystals. These types of nanoparticles were obtained with a cluster source based on magnetron sputtering and gas aggregation, by supplying the magnetron discharge with continuous or pulsed wave radiofrequency power. Detailed morphological and microstructural studies were performed. The hexapod particles present a dendritic growth while the faceted ones have a single crystal structure. The α-W and β-W crystalline phases are present in both types of nanoparticles; nevertheless, the β-W structure is dominant for the hexapod ones. Although the β-W phase is usually metastable, we observed its unexpected long term preservation in hexapod nanoparticles. The results, added to previously reported nanoflower-like particles, point out the ability to control the shape and structure of the tungsten nanoparticles using the magnetron sputtering gas aggregation technique.
•Tungsten nanoparticles produced in a tokamak of tungsten divertor.•Micron-sized tungsten dust particles emitted during off normal events.•Helium nanobubbles produced at the surface of tungsten dust ...particles of a tokamak.
Two populations of dust particles were found during the first phase of operation of WEST. The one that dominates by size and weight comes from the delamination of tungsten coatings covering graphite tiles and the emission of droplets of molten materials during off-normal events. Sizes vary from several microns to tens of microns. More generally, micron-sized dust particles due to the erosion of all materials present in the vacuum vessel were collected. In addition, nanocavities were found at the surface of tungsten dust sampled after He plasmas and were attributed to He trapping in the form of nanobubbles. Tungsten nanoparticles constitute the second unexpected dust population. They are dominant by their number and were essentially found at the surface of micron-sized particles. They may result either from the condensation of an oversaturated vapor above molten tungsten or come from ion-neutral clusters growing in plasma regions of low temperature until the appearance of solid particles.
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