Tritium absorption/desorption in ITER-like tungsten particles

Abstract

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 character-ization of tungsten particles and on a comparative analysis of tritium absorption/desorp-tion 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.

Synthesis of tungsten nanopowders: Comparison of milling, SHS, MASHS and milling-induced chemical processes

“…1, neither crystallized oxide phase nor tungsten carbide impurities from the milling media could be detected, although X-ray photoelectron spectroscopy (XPS) revealed the presence of oxide films on the surface of W particles [1]. Using Rietveld refinement, the obtained average crystallites size is 4 nm with a micro-strains level around 0.3%.…”

“…Therefore, the 10 min pre-milling seems to have the best synthesis conditions, even better than milling-induced chemical reaction, the lowest O fraction being under 10% which represents a fraction of oxidized W atoms (WO 2 and WO 3 ) lower than 5%. Further reduction of these oxides has been proved to be possible without altering the nanostructure of the powders, using an hydrogen atmosphere at 475°C [1,2]. However, an indisputable explanation of why the optimum oxygen content is observed with a 10 min milling pretreatment is difficult to do.…”

“…In previous papers we started to study the behavior of different kinds of tungsten particles towards 3 H [1,2], and in presence of hydrogen plasma [3]. The present paper aims at providing more insights on their preparation.…”

“…Unfortunately, the availability of tokamak-retrieved powders is quite low. Therefore, in order to conduct the different studies to assess the potential dangerousness of tungsten nanopowders, including their behavior when in presence of tritium, or when facing a hydrogen plasma [1][2][3], or their cytotoxicity or their genotoxicity (study currently under progress), other means of production must be sought for. Moreover, as ITER will be a significantly larger tokamak than the presently existing ones, different morphologies might occur during its operation, and thus it would be preferable to obtain a set of different morphologies to make sure the worst case scenario can be handled.…”

Partial and total dielectronic recombination rate coefficients for W55+to W38+

“…Beryllium coated tiles will line the wall of the main reactor vessel due to their low erosion rate and the low tritium retention of Be. Tungsten (Z = 74) will be used in regions of high power-loads, such as the divertor chamber at the base of the main vessel, and it is also resistant to tritiation [3]. On the downside, such high-Z elements are efficient radiators and must be kept to a minimum in the main plasma to avoid degrading its confinement.…”