A Transfer Model of Tritium in a Local Hydrosphere

For purpose of dose estimation a transfer model of tritium as well as some other important radionuclides that occur in the environment is being developed in our institute. Tritium is considered to be a significant source of internal exposure for man. Our present work is focussed on designing a tritium compartment model of the local hydrosphere. Our concept is based on the seven-box model of the hydrological cycle on a global scale that was proposed by National Council on Radiation Protection and Measurements (NCRP). To estimate the impact of nuclear facilities in a local area, geographical and geological conditions need to be taken into consideration. Therefore in present work, groundwater reservoir was divided into three layers and then the transfer coefficients were determined by analyzing time-series data on fallout tritium concentrations in the local environmental water. The most important difference between the NCRP model and ours is that the tritium metabolism of aquatic plants, invertebrates and fish is taken into consideration. For these aquatic organisms there are two sub-compartments, namely tissue free water tritium (TFWT) and organically bound tritium (OBT). We developed this model because the living organisms in such aquatic systems are utilized as fishery products by the Japanese people. The effect of the fast intake of HTO by aquatic plants was demonstrated by a preliminary application of this model.