Helium thermal desorption and retention properties of V–4Cr–4Ti alloy used for first wall of breeding blanket

Abstract

Helium irradiation experiments of V-4Cr-4Ti alloy with various surface treatments were conducted in an Electron Cyclotron Resonance (ECR) ion irradiation apparatus.After helium ion irradiation at room temperature, the helium thermal desorption and retention properties were examined by thermal desorption spectroscopy (TDS). Ion energy of helium beam was 5 keV. Three groups of desorption peaks appeared at around 500, 850 and 1200 K in the TDS spectrum. After helium ion irradiation at ion fluence of 1x10 21 He/m 2 , the retained helium desorbed mainly at around 1200 K and all of the implanted helium atoms were retained. With increasing fluence up to 5x10 21 He/m 2 , the amount of helium desorbed at 500 K increased. For the polished samples with annealing at various temperatures, the desorption peak observed at around 500 K shifted to higher temperature region. Smallest retained amount of helium was observed in the V-alloy with polishing followed by annealing at 1373 K.

Retention and desorption behavior of helium in oxidized V–4Cr–4Ti alloy

“…The oxygen concentration in the near surface region of the non-oxidized sample was comparable with that of the cold-rolled V-4Cr-4Ti, while the carbon concentration was lower than that of the cold-rolled sample [8]. Compared to the annealed sample [8], the oxygen concentration at the near surface of the non-oxidized sample was higher, while the carbon concentration was roughly the same. The thickness of the oxidized layer in the non-oxidized sample was evaluated to be 18 nm, which is shallower than that of the projected range of 5 keV helium ions ($27 nm).…”

“…This sample is referred to as 'oxidized sample'. Pre-treatment procedure of 'annealed sample', which was V-4Cr-4Ti sample annealed at 1373 K for 1 h in a vacuum [7,8], is also shown in Table 1 to be compared with the oxidized and the non-oxidized samples. The depth profiles of atomic composition in the oxidized and the non-oxidized samples were analyzed by using Auger electron spectroscopy, AES, with 3 keV-Ar ion etching.…”

“…The depth was estimated by using the sputtering yield of pure vanadium of 3 keV Ar ion [15]. The oxygen concentration in the near surface region of the non-oxidized sample was comparable with that of the cold-rolled V-4Cr-4Ti, while the carbon concentration was lower than that of the cold-rolled sample [8]. Compared to the annealed sample [8], the oxygen concentration at the near surface of the non-oxidized sample was higher, while the carbon concentration was roughly the same.…”

“…In addition, the V-alloy is exposed to helium glow discharges employed for wall conditioning such that it is irradiated by He ions with different energies. In a previous study, it was found that many blisters were formed on the surface of vanadium alloy after helium ion irradiation with high ion fluence at low temperature [6][7][8]. If the blisters and internal bubbles are formed, the retained helium reemits into the plasma and then fuel dilution may take place.…”

“…It was also reported that impurities enhanced helium retention owing to formation of He n VX and/or He n V m X type defect clusters related to impurity (X) [8,10]. Furthermore, it is well known that the vanadium alloy, as well as vanadium, is easily oxidized [12].…”