From a scientific and environmental point of view, understanding how environmental factors and impacts, including anthropogenic ones, can affect the hydrology of rivers, their water quality and related to river basin ecosystems is essential. At the moment, there is an increased interest of possible emissions from the Belarusian nuclear power plant (NPP) and the response of the environment to them. Whereas the probability of sudden incidents of a large impact on the environment at nuclear power plants are minor, but when they occur lead to different level consequences due to sudden and strong destructive properties. One of the purpose of this work would be to create a predictive model of the Neris River assessing the impact of possible events leading to environment pollution. With the consequences of such events, we must learn to live, at least reasonably from a scientific point of view. Also, based on isotopic studies of the water system, to develop a dynamic model for tracking pollution sources, which could characterize the relationship between the water system and the source of risk, is of primary importance.
River systems are very complex, so modeling is one of the important tools that can show the impact of different events under different conditions. The developed risk assessment model would be an effective tool for systematically quantify random uncertainty due to processes in the river system, as well as providing information when making decisions on the control of sudden water pollution, identifying critical sources and quantities of pollution. For the implementation of the work, isotopic research methods and a modern modeling program would be used.
The importance of the transfer of tritium in aquatic ecosystems was highlighted in studies performed in Canada and France (CNSC 2010; ASN 2010). Calibration of the transport model according to tritium data in rivers and modeling of the groundwater age was carried out in the western basin of Lake Taupo, New Zealand (Gusyev et al. 2013). To better understanding the transport process simulation of HTO from surface water to the atmosphere was carried out (Marang et al. 2011). Modeling of groundwater discharges into the river based on radon mass balance using tritium data was performed on the Elbe River, Germany (Schubert et. al 2020). The characterization of water systems is therefore an important for both issues such as construction of new nuclear power plants and the decommissioning of old ones. Transport models realize a mathematical description of the movement of radionuclides in a particular component of the environment (air, surface water, groundwater, biota) the purpose of which is to predict the concentration of radionuclides. In Lithuania, investigations of water systems using modelling tools were carried out mostly in relation to groundwater. Number of studies have focused on the formation of groundwater in the Baltic Artesian Basin (Vaikmäe et al., 2001; Cheban, 1966; Mokrik and Vaikmäe, 1988, Mokrtik et al. 2014; Mokrik and Samalavičius, 2021). The research interests include various aspects of palaeohydrogeology, origin issues and formation scenarios. Isotopic studies of the hydrological cycle including precipitation, streams and lakes, groundwater and other water bodies were performed since the beginning of operation of the Ignalina Nuclear Power (Jakimavičiūtė-Maselienė et al. 2012; Vaitkevičienė et al. 2013; Mazeika et al. 2013; Jefanova et al. 2018).
Because of the tritium mobility in hydrological cycle and well-known atmospheric abundance it is of great importance in line with other mobile radionuclides to carry out tritium measurements in the water bodies surrounding nuclear facilities and use data fot the environmental quality and risk assessment.