Interception and uptake by plants leaves of tritium from precipitation

The Radiological and environmental impact assessment models are used for evaluating the radiological impact of actual and potential releases of radionuclides into the environment. For tritium, a special radionuclide that readily enters into many organic forms, the processes involved in its interception and uptake by plant leaves during a tritiated rain are complex and not yet well understood. When rain containing tritiated water (HTO) starts, water is retained progressively on leaves up to a maximum storage capacity and also evaporates from the wet canopy part. The dynamics of leaf HTO concentration depends also on rain intensity and duration. In the absence of experimental data for leaf HTO concentration due to tritiated rain, various processes of potential importance are presented. Processes such as: leaf interception during rain event, interaction between drops and leaf surface, and extension of water layer (adhesion fraction) are described in the present study. Recent results on pesticide spray and sprinkler irrigation experiments and modelling approaches are used, because they provide useful information for the interaction between water droplets and the leaf surface. The rain drop diameter distribution and the associated drop falling velocity are linked with the washout studies and past results for tritium are used. The main crops (i.e. wheat, maize, barley, soybean, oilseed rape, and grape) around Cernavoda Nuclear Power Plant (Romania), operating two CANDU 6 units with high tritium loads are considered. For radiological impact assessment of tritium, the tritiated rain on crops at harvest for normal and/or short term and intense tritium release are presented.