Prediction of tritium behavior in the atmosphere and assessment of radiological impact

Abstract

We have developed a computer program ATDC (Atmospheric Tritium Dispersion Code) to predict downwind tritium air concentrations in the environment around nuclear power plants on the basis of the Gaussian plume model. The tritium air concentrations by field measurement (measured tritium air concentrations in the areas adjacent to Wolsong Unit 1, a pressurized heavy water reactor ; PHWR) were compared with that by calculation to validate the program. The predicted and measured atmospheric tritium concentrations were quite consistent in trend and magnitude. This computer program will be useful in reviewing and evaluating environmental radiological impacts for PHWRs. Especially, it will be of great help to predict the behavior of tritium in the atmospheric environment around nuclear power plants. We also have studied the distribution of environmental tritium and the correlation coefficients between tritium concentrations in several environmental samples and the emissions of tritiated water vapor from Wolsong Unit 1. The annual mean concentration of atmospheric HTO were in the range of $1.31 \sim 29.2 Bq/m^3$ and the long-term atmospheric dilution factors were in the range of $10^{-7} \sim 10^{-6} s/m^3$. Annual mean concentrations of tritium in groundwater were in the range of 19.2 ~ 27.9 Bq/l at N-1 and 64.1 ~ 189 Bq/l at S-2, and were generally less than 0.2 % of MPCw (222 kBq/l). The concentrations of tritium in precipitations exponentially decreased with the distance from Wolsong Unit 1, falling to current global levels at about 25 km off-site. The highest concentration of tritium in soil moisture was observed in May and June, when the relative humidity was high. The concentrations of tritium in soil moisture were higher than those in precipitations.