Bezhenar R. Information technologies of aquatic ecosystems contamination modeling for the computer support of decisions in radiation safety

The thesis focuses on the development and improvement of information technologies for the systems of computer support of decisions in radiation safety based on the new and upgraded mathematical models for the contamination transport in aquatic ecosystems and dose effects on humans through different pathways of irradiation. For this purpose, the box model POSEIDON-R was improved for using in systems for the computer support of decisions in radiation safety. In particular, the model of the benthic food web has been developed where the transfer of contamination from bottom sediments to marine organisms is considered for the first time. A new kinetic-allometric model for non-uniform assimilation of contamination by fish, developed within the thesis, allows to consider the chemical-biological features of contaminants to accumulate in certain tissues of the organism. Model parameters describing the main metabolic processes depend on mass of fish to the -¼ power that is in agreement with the general scaling law in biology. In addition, the dependence of cesium and strontium uptake rates by marine organisms on the salinity of surrounding water that means the concentration of competition ions potassium and calcium, respectively, is obtained. Such improvement of POSEIDON-R model allows it to be used in water bodies with a wide range of salinity, including estuaries with almost fresh water and seas with large river water runoff. The customization of POSEIDON-R model to different regions of World Ocean was the necessary step for its integration in the RODOS system. For this purpose, it was applied for long-term simulation of the transfer of radioactive cesium 137Cs in the European seas and seas of Northwestern pacific significantly contaminated in result of the accidents at the Chornobyl and Fukushima nuclear power plants. For every region, the calculated concentrations of radionuclide in the water, bottom sediments and marine organisms agree with the corresponding measurements throughout the simulation period. A three-dimensional model THREETOX was used for detailed reproducing the transfer of radioactive contamination in the Northwestern Pacific over two years after the Fukushima nuclear accident and in the Baltic Sea during the five years following the Chornobyl accident. It provides maps for 137Сs concentrations in the marine environment and directions for its propagation at different times. To reproduce the transport of 137Сs in marine organisms of Pacific Ocean following the Fukushima nuclear accident and to predict the effects of future accidents, the components of modelling technology for aquatic ecosystems contamination were integrated for the first time in three-dimensional model THREETOX. The box model POSEIDON-R was incorporated into the PREDO platform to estimate radiation doses to the public resulting from the releases of radionuclides in the marine environment during normal operation of nuclear facilities in Sweden. The calculated concentrations of radioactive 60Co and 54Mn in the water, bottom sediments and marine organisms are compared with the corresponding measurements for the Forsmark NPP located on the Baltic Sea coast. The developed kinetic-allometric model for the for non-uniform assimilation of contamination in fish gives better agreement of the calculated concentrations for both radionuclides with measurements for fish species at different levels of the food chain compared to other models. This is caused by the contribution of different tissues, because even a low concentration of activity in muscle tissue significantly affects the total content of radionuclide in fish due to its large mass fraction. The FDMA model was integrated into the RODOS system for calculation the doses received by the population from freshwater pathways of irradiation. It provides the dose assessment due to consumption by people of the drinking water and food products of plant and animal origin contaminated through freshwater. The input data for the model is the concentration of radionuclides in the water on agricultural and habitat areas, which is the output information of the RODOS hydro module. Model parameters related to different radioecological regions of Ukraine were collected from open sources, processed and integrated into the RODOS system that was contributed to its implementation in Ukraine. Nowadays, the dose assessment for population from freshwater pathways of irradiation using the RODOS system is carried out at the nuclear facilities of Ukraine and in governmental structures. In particular, it is in operate at the Rivne NPP and in the Radiation Accidents Consequences Prediction Center of the Ukrainian Hydrometeorological Center that is confirmed by the relevant acts of implementation.