Hydrogen Adsorption Behavior on Stainless Steel for Cooling Pipe in Fusion Reactor

To investigate the hydrogen behavior in/on the Stainless Steel (SS)-304, the deuterium or heavy water was sorbed on the sample by various methods, such as water adsorption, ion irradiation and electrolysis, and the chemical states of iron, chromium, nickel and oxygen were studied by means of X-ray photoelectron spectroscopy (XPS). It was found that the metal oxide and oxyhydroxide, FeOOD or CrOOD, were formed on the surface of SS-304. The oxyhydroxide was dominant on the surface of the sample charged by electrolysis. However, metal oxide was observed on the surface of SS-304 after D₂O water adsorption. The thermal desorption spectroscopy (TDS) was also applied to the evaluation of the thermal desoprtion behaviors of D₂ and D₂O from SS-304. It was found that three peaks were found in the sample charged with electrolysis. Among them, two peaks were also observed in the sample with water adsorption. The first peak, which was only found in the sample charged with electrolysis, suggests the D₂ and D₂O release by the decomposition of oxyhydroxide, and the second peak was induced by the decomposition of hydroxide or aquo-iron complexes. The third deuterium release would be induced by the desorption of the dissociative absorbed deuterium. It was concluded that the existence and chemical form of oxygen influence the retention of deuterium on/in SS-304.