Deuterium retention of V–4Cr–4Ti alloy exposed to the JFT-2M tokamak environment

Vanadium alloy (V–4Cr–4Ti) samples were exposed to JFT-2M tokamak environment during deuterium plasma discharges including 200 divertor shots for 9 months operation period. In this environment, the samples are not directly exposed to deuterium plasma, and are exposed to high-energy particles, i.e., D and D2 including impurity species. The deuterium amount retained was 2×1017 D/cm2 (1.3 wppm), which is only one order of magnitude larger than that found in the exposed SS304 sample. This concentration is sufficiently low not to cause the hydrogen embrittlement. A layer about 200 nm which was found to contain Ti, O, C, Fe and Cr was observed on the surface of the exposed sample. To investigate the effect of oxidation unexposed V-alloy samples were oxidized under a condition of low oxygen pressure (0.05 Pa) and low temperature (⩽723 K). After the oxidation, titanium segregation in the surface region was observed. The content of absorbed hydrogen in the oxidized sample having a thick Ti-oxide layer (⩾100 nm) was one order of magnitude smaller than that of unoxidized sample under a given absorption condition.