Chromatographic Analysis of Molecular Hydrogen (H2) in the Atmosphere for Understanding Atmospheric Tritiated Hydrogen (HT)

Tritium monitoring would be required at the site of the fusion test facility from the viewpoints of radiation safety and public acceptance. As one of the tritium monitoring items, atmospheric tritium monitoring in the environment is conducted and has three chemical forms: tritiated water vapor (HTO), tritiated molecular hydrogen (HT), and tritiated methane (CH3T). It is well-known that the specific activity of HT and CH3T is much higher than that of HTO. To investigate the cause of high specific activity, we focus on the behavior of molecular hydrogen (H2) in the atmosphere and develop a measurement system based on a gas chromatograph. Monitoring results showed that the range of the H2 mixing ratio at the NIFS Toki site was 0.4∼0.6 ppm over the observation period. Atmospheric H2 concentrations were higher during the daytime and long daylight seasons, suggesting the generation of hydrogen by photochemical reactions. Preliminary results suggest that there does not appear to be a clear correlation between the concentration of atmospheric HT and the concentration of H2 in the atmosphere. This suggests that the source of HT is different from the source of H2 in the atmosphere.