Studies on the rain scavenging process of tritium in a tropical site in India

This study presents the results of one of the first systematic experiments on tritium ((3)H) concentrations in ground level air against that in rainwater near a pressurized heavy water reactor in a tropical region. The samples were collected over the rainy season of three years (2007, 2008 and 2010). For this study, 31 data sets were collected and interpreted based on the theoretical information available in the literature. The specific activity ratio of (3)H between rainwater and air moisture at ground level was calculated for each data set. The average specific activity ratio was found to be 1.96 ± 2.72. A correlation (r = 0.82, p < 0.001) was observed between the total rain hours in a day and the rainwater (3)H activity. Higher rain duration with slower rain rate yielded higher (3)H concentrations as more time was available for the scavenging/wash out process to take effect together with lower dilution. The present data also suggested the need to further investigate the influence of raindrop distribution and other local meteorological parameters on the (3)H wash out process. An attempt was also made to predict the (3)H concentration in air moisture samples using a Gaussian plume dispersion model and the values were compared with the measured (3)H activity. The measured values were generally lower than the predictions.