Re-emission of heavy water vapour from soil to the atmosphere

Yokoyama, Sumi; Noguchi, Hiroshi; Ichimasa, Yusuke*; Ichimasa, Michiko*

The reemission process of tritiated water (HTO) deposited on a soil surface is an important process to assess tritium doses to the general public around nuclear fusion facilities. A field experiment using heavy water (HDO) as a substitute for HTO was curried out in the summertime to investigate the reemission process of HTO from soil to the atmosphere. In the experiment, the time variations of the depth profiles of HDO concentrations in soil exposed to HDO vapour and soil mixed with HDO were measured during the reemission process on the field. The decrease of HDO concentration insoil water of exposed soil was much greater than that of mixed soil. The reemission process was analysed using a model including the evaporation of HDO from soil, the exchange between the soil HDO and air HO, and the diffusion of HDO in soil. It was found that the model is applicable to calculating the time variations of detailed depth profiles of HDO concentration in soil water in surface soil layers.