Speaker
Description
Keisuke Mukai,1,2*, Kosuke Kataoka3, Juro Yagi3, Motoki Nakajima4, Jae-Hwan Kim4, Takashi Nozawa4
1 National Institute for Fusion Science, National Institutes of Natural Science, Toki, Gufu 509-5292, Japan
2 The Graduate University for Advanced Studies, SOKENDAI, Toki, Gifu 509-5292, Japan
3 Graduate School of Energy Science, Kyoto University, Uji, Kyoto 611-0011, Japan
4 National Institutes for Quantum Science and Technology, Rokkasho, Aomori, Japan
In ceramic breeding blanket, reduced activation ferritic/martensitic steel (RAFM) structural steel is corroded by vapor gas released from tritium breeder (Li-containing ceramic pebbles), resulting in a significant reduction of the fatigue lifetime. To understand the corrosion kinetics and the effect of moisture absorbed in the breeder pebbles, the corrosion test of F82H by LTZO (Li2+xTiO3+y solid solution with 20 wt% Li2ZrO3) pebbles were conducted at 773–998 K. Microstructural analysis was conducted using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Element depth profile and structural analysis using glow discharge optical emission spectroscopy (GD-OES) and X-ray diffraction (XRD) identified the corrosion products has cubic, spinel, and rhombohedral structures with the compositions of Li–TM–O (TM: transition element in F82H). In the long-term compatibility test for up to 672 h, the growth of the corrosion layer thickness followed a parabolic law at 833 K, yielding apparent diffusion coefficient of 6.95 × 10–13 cm2/s. A rapid growth of the corrosion layers was observed at 993 K after 380 h which could be triggered by failure of the protective layer. A comparison of diffusion coefficients with the reported data indicated predominant effects of temperature and impurity concentrations in the sweep gas on the corrosion, while the composition and shape of ceramic breeder had minor influences. The apparent diffusion coefficients obtained in this work were similar to those of gas-oxidation of Fe-Cr alloy. The estimated thickness of the corrosion layer was only 5.8 μm at 623 K after 2 years. The effect of corrosion on fatigue behavior of F82H steel will be assessed in our future study.
