Deuterium permeation of low-activation vanadium alloys possible for reuse in a short time in fusion reactors

Abstract

Low-activation vanadium (V) alloys are alternative to reduced-activation ferritic/martensitic steels for the blanket structural material. To make the reusage of the alloys possible in a short time, new-design concepts of V alloy have been suggested in National Institute for Fusion Science. In the present study, the deuterium permeation properties of the new-designed V alloys were investigated.The new-designed V-4Cr-4Ti alloy samples with high and low purity, named H44 and L44, respectively, were used. For comparison, the NIFS-HEAT-2 V alloy samples, named NH2 were also used.It was found from the permeation experiments that deuterium permeability coefficient of L44 was smaller than that of NH2, while the permeability coefficient of H44 was comparable with NH2. These results suggest the permeation coefficient of D of the new-designed V alloy was similar to those of the conventional V alloy, if Ti and O content was the same. Estimated activation energies of diffusion and permeation indicated that the permeation behaviors significantly depended on titanium oxides at the surface and in the bulk. Data obtained by a microscope with Auger electron spectroscopy indicated that the concentration and the composition of the oxide must change with air exposure during the maintenance and with hydrogen isotope exposure during the reactor operation. The obtained results suggest these changes of the concentration and the composition result in the change in the permeation characteristics of hydrogen isotopes.