Pushkarev O. Geochemistry of tritium in natural-anthropogenic biogeosystems

The thesis is devoted to the determination of the laws of technogenic transformation of the balance of tritium in natural and technogenic biogeosystems, the study of ways and agents of migration and the laws of immobilization of tritium in the biotic and abiotic components of landscape-geochemical systems in the tritium emission areas. The transfer of atmospheric and water flows leads to a dilution of the concentration of tritium in the environment of transit agents in the background levels. A significant source of tritium is radioactive waste storage (RWS), where significant amounts of this radioactive isotope of hydrogen are concentrated. Deficiencies in the protective structures of storage facilities lead to a violation of their tightness and the release of tritium into the environment in the form of gas-aerosol emanations and hydro-geofiltration flows through a discontinuity of engineering barriers - floors, walls and bottom of the storage. After extraction from the air and deposition on vegetation and soil surface, tritium is included in the short-term and long-term circulation in the natural-manmade biogeosystems. The atmogeochemical flow from the sources of tritium into the environment causes a coordinated process of accumulation of tritium in transpirational water (TW) and in an organically bound tritium (OBT) in the grass and in the leaves of perennial vegetation. The correlation coefficients between tritium in TB and OBT for grass are 0.98 and for leaves are 0.89. The process of tritium transpiration may be accompanied by the cumulative effect of the formation of OBT. In the zone of influence of the preservation station of the Kiev Interregional Special Plant, the content of OBT predominates over the tritium content in TV in perennial vegetation by 29% and in annual vegetation by 14%. The adsorption capacity of the biotic component of local landscape-geochemical systems is estimated. The total stock of tritium accumulated in the OBT of phytomass at the elemental site (in the herbage and perennial vegetation as a whole) can exceed 900 Bq×m–2. The rate of hydrogen isotope exchange in the process of photosynthetic metabolism of tritium by vegetation from an aqueous solution was first experimentally estimated. The kinetic parameters of the metabolic formation of OBT by plants from an aqueous solution were calculated. The patterns of tritium immobilization from hydrogeofiltration flows on geochemical barriers are determined. The adsorption capacity of local blocks of the geological environment in the areas where objects from which tritium is released is calculated. When tritiated water is filtered, the elementary unit of the geological environment is able to extract tritium in the amount of up to 55,000 Bq×m–3, incl. reliably fix in the structure of clay minerals more than 7000 Bq×m–3. The kinetic parameters of tritium filtration and adsorption-desorption processes in dynamic water-mineral systems with used of typical clay minerals (structural types 1: 1, 2: 1 and minerals with modulated layers with joined strips) and finale hydrogen radioactive isotope immobilization in their structures was experimentally investigated. In stationary model water-mineral systems created from clay minerals (kaolinite, montmorillonite, saponite, palygorskite and sepiolite) and tritiated water, was established the effects of hydrogen-isotopic fractionation with the maximum fractionation factor in montmorillonite α = 1.28 with surface adsorption, α = 1.28 at the molecular HTO → H2O exchange in the interlayer space of montmorillonite and α = 1.24 in the structural OH positions. The effect of isotope osmosis was first found when using ion-conducting montmorillonite membranes in an aqueous system consisting of distilled protium (H2O) and tritiated (“HTO”) water. It is established that the behavior of the fluid in the cell above the bentonite membrane depends on the isotopic composition of water in the cell and reservoir. The maximum isotope-osmotic pressure in the aquatic environment was 0.29 kPa. The electrochemical isotope-hydrogen fractionation effect in aqueous solution using mineral and composite cellulose-mineral membranes was first experimentally established. The greatest fractionation effect was obtained using a montmorillonite-cellulose membranes with a 50% of clay mineral (Δ = 278 Bq). The effect of fractionation of hydrogen isotopes was observed during electroosmotic filtration of tritiated electrolyte through low-permeable clay membranes, with a maximum value of α = 1.16 in the montmorillonite. It is proposed to conduct further research to refine the design of electroosmotic equipment, and to search for or create new, more efficient proton-conducting substances that can be used as electroosmotic membranes oriented specifically to the fractionation of hydrogen isotopes.