Dispersion of Liquid Effluents from NPP in Sava River

To estimate the activity concentrations of the radionuclides downstream the Sava river due to the liquid discharges from the Krsko NPP, a modified IAEA SRS-19 model was adopted in 2003. The in-site (WMT and SGBD water) measured values enter as the input data for the model. Related to the inventory of the Krsko NPP liquid discharges, only tritium activity concentration in Sava river can be detected above the detection limit. Thus, 3H measured values could serve as the key element for the comparison of modelled and the measured data. In this study we took detailed in-site measured data to calculate the activity concentration of 3H in Sava river using the model. The calculated values were compared with off-site 3H measurement results at Krsko, Brezice and Jesenice na Dolenjskem sampling sites obtained from 2009 to 2015. Various hydraulic and hydrodynamic parameters of the Sava river were considered. To validate the fit, the 3H measurement results obtained by the case study carried out in 2008, where the liquid discharge was tracked downstream at several other locations, were used. It was found out that complete vertical mixing in Sava river probably occurs immediately after the NPP dam. Continuous sampling at Brezice suggests that complete lateral mixing likely occurs before Brezice, while the study of tritium measurements along the Sava river at location 5 (old bridge in Brezice -Sernova cesta) does not support this theory and suggests that our current model might be improved. (author).