Buffering properties of the geological environment have been investigated on the example of radioactive waste repository. The natural-technogenic system is presented by a source of tritium, the migration medium, and the drainage system of the nearby stream. Our experiments show that clay minerals are the main tritium absorber in the loessy loam. Tritium accumulation occurs not only on the surface and in the interlayer spaces of clay minerals, but also in their structural OH-groups. In the "water - mineral" system, equilibration of heavy hydrogen isotopes concentrations between water and OH-groups, free- and interlayer water of clay minerals takes place. The direction of hydrogen isotopes exchange depends on the ratio of heavy isotope concentration in a mineral and its concentration in water. The tritium accumulation rate in montmorillonite's structural OH-groups under natural conditions, quantitative characteristics of tritium immobilization and mobilization have been determined. It has been established that the variation of dynamic parameter of hydrogen isotopes' exchange depends on tritium concentration in water phase and on duration of interaction between water and mineral phases.
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