STUDY OF TRITIUM MIGRATION AND RETENTION MECHANISMS IN THE GEOLOGICAL ENVIRONMENT (BY THE EXAMPLE OF THE KYIV RADIOACTIVE WASTE STORAGE FACILITY)

Abstract

Radioactive waste storage facilities (RWSF) are a potential source of tritium in the biosphere. Engineered concrete constructions are not sufficiently reliable forasmuch as water leaks contaminated with tritium from the storage facilities into the geological environment has been detected. The barrier properties of the natural environment at the storage sites are determined by the ability to absorb and retain heavy isotopes of hydrogen during a considerable period of time and thus exclude its circulation in the biosphere. Various elements of the natural ecosystem take part in the absorption of tritium – the geological environment, soil organic matter, annual and perennial vegetation, micro- and macrobiota. A certain part of tritium in the gaseous and aerosol form is released into the air. The highest concentrations of tritium are recorded in the area close to the concrete radioactive waste (RW) storage facilities, where the vapor-gas emanation plume is least dispersed. With distance from the storage facilities, the tritium concentration in the soil humus layer significantly decreases due to the spatial dispersion of the tritium in the atmospheric plume. Tritium from the air enters the soil with the atmospheric precipitation and is partially retained in the humified layer of the soil. Most of the tritium from the atmospheric precipitation is transported by the vertical infiltration flow through the sedimentary layers represented by loess sandy loams and loams, where it is finally retained. In the area close to RWSFs, the concentration of heavy hydrogen isotope in pore, interstitial and film water (1 fraction) is up to 87 % of its total content in an elementary block. In the more tightly bound forms (2 and 3 fractions), it is 9 % and 4 %, respectively. Farther from the RW storage facilities in the predominant air flow direction, the tritium concentration in free water decreases to 75 %. In this area, more intensive redistribution of tritium between the structural sites is observed. At the more distant monitoring points (wells), from 25 % to 37 % of the total tritium amount in the soils is retained in more tightly bound forms in the structure of rock-forming, mainly clay minerals.