In order to investigate the function of water molecule for tritium transport behavior on the water-metal boundary, a series of experiments of tritium permeation into humid atmosphere was performed through pure iron piping with different surfaces of oxide etc., which contained about 1 kPa of pure tritium gas at 423 K. Chemical forms of tritium permeated into water were monitored continuously under purging outer jacket by <1000ppm of water vapor in Ar. Observation of metal surfaces was also carried out by Secondary Electron Microscope (SEM) and X-Ray Diffraction (XRD) analysis. The results were compared with those permeated into pressurized liquid water at 423 K.

The actual tritium permeation rate into Ar with <1000 ppm of water vapor was not clearly changed that into liquid water. In the vapor atmosphere, a magnetite layer did not grow on the surface clearly, and tritium permeation rate and chemical species (∼100% of HTO) through pure iron piping with mechanically polished surface were not changed drastically comparing with data with a magnetite surface. On the other hand, hydrogen gas (HT) fraction of tritium permeated into the outer jacket increased drastically in case of a gold plating surface.