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Substantiation of the suitability of the subsoil area for the construction of a radioactive waste repository in deep geological formations is a consequential multistage process, including the studies on the scale of "district", "site", "plot". In near future in Russia it is planned to start work on sinking permanent mine openings of the underground research laboratory (URL). The purpose of this article is to provide a brief analysis of international and local research experience in underground research laboratories and their equivalents, as well as the deep geological repository (DGR) safety requirements to determine the scope of work on scientific and technical support for the URL construction. A brief review of the applied research methods is presented on the following aspects: Parameters characterizing structural and tectonic condition of the rock mass-rupture zones, fracture zones of various origins, monolith areas; geomechanical characteristics (stress-strain state, deformability and strength); hydrogeological characteristics of the mass elements and groundwater flow patterns; characteristics of the physical and chemical processes of interaction between groundwater and rocks and materials of engineering barriers.

Consideration of geodynamic, hydrogeochemical, erosion and other quantitative characteristics describing evolutionary processes in a rock mass is carried out when choosing a geological formation for the disposal of radioactive waste. However, the role of various process parameters is not equal for safety ensuring and additional percentages of measurement accuracy are far from always being of fundamental importance. This makes it necessary to identify various types of indicators of the geological environment that determine the safety of radioactive waste disposal for their detailed study in the conditions of the burial site.An approach is proposed to determine the priority indicators of physical processes in the rock mass that determine the safety of disposal of various types of radioactive waste and require increased attention (accuracy, frequency of measurements) when determining in-situ conditions. To identify such factors, we used the sensitivity analysis method that is a system change in the limits of variable values during security modeling in order to assess their impact on the final result and determine the role of various physical processes in ensuring safety.It is shown that the safety of isolation depends on various factors when burying "natural", "short-lived", and "long-lived" groups of nuclides. The factors that greatly affect safety when disposing of radioactive waste of these types are highlighted. The list of parameters of the geological environment that characterize the priority mechanisms of localization of various types of radionuclide contamination during burial and requiring the most detailed determination in full-scale conditions is defined.

Rock mass is considered as a natural barrier impeding the release of radioactive waste into the environment, being part of a multi-barrier system designed to ensure the safety of deep disposal facilities for radioactive waste (DDF RW). A number of regulatory documents [1] and recommendations [2, 3] states the importance of the geological medium, namely, its characteristics for the long-term safety of RW disposal. Current stage of URL development project is specifically focused on providing the opportunities for geological research covering target RW disposal horizons solely via borehole methods before the entire complex of underground excavations is formed. Due to long-term operation of wells and their initial design features, the state of some of these wells has appeared to be unsatisfactory requiring reconstruction. In addition, in accordance with certain legislative requirements, all wells shall be abandoned after relevant operations have been completed. The article discusses the reconstruction and abandonment of wells drilled at the Yeniseiskiy site. It demonstrates the feasibility of proposed designs providing the opportunities for further expansion of studies to investigate the state of rocks under natural conditions and to arrange for monitoring. The paper provides an evaluation and comparative analysis of plugging materials proposed to be applied under well abandonment operations.

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