_applied sciences_  
_Article_  
**Bentonite-Concrete Interactions in Engineered Barrier Systems during the Isolation of Radioactive Waste Based on the Results of Short-Term Laboratory Experiments**  
**[PERSON] 1,*\({}^{\text{\text{\textminus}}}\)**, [PERSON] 1,2\({}^{\text{\textminus}}\)**, [PERSON] 3, [PERSON] 1, [PERSON] 1,4, [PERSON] 2,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,19,18,19,  
waste (HLW) from the biosphere. Waste disposal in geological formations must reliably isolate RW from the biosphere over very long periods of time and guarantee that the concentrations of residual radioactive substances reaching the biosphere are insignificant in comparison to the natural background levels of radioactivity. In addition, DGRs must provide sufficient confidence in the minimal risk of occasional human interference. Most concepts of RW isolation from the biosphere are based on passive multibarrier systems. Such systems usually include a natural geological barrier created by rock formation, wherein the repository/disposal is built, along with a complex of artificial (engineered) barrier safety systems (EBSs). Such a principle of multibarrier protection ensures complete system reliability wherein safety is upgraded using materials with different properties, for example, corrosion-resistant materials for RW isolation and/or materials with low permeability for limiting the ingress of groundwater. Within the application of an artificial multibarrier system, at the present time, bentonite or a mixture of bentonite and sand is used in the vast majority of developing concepts as a buffer material, arranged between waste containers and host rock or used for sealing the premises of an underground repository [2; 3; 4]. In such cases, the buffer material may be produced for use in different areas in the form of compacted pellets, such as in a Swiss project [6], or in the form of compacted (pressed) bentonite [2; 7]. The key requirements for buffer materials used in the disposal of HLW include low water permeability, the ability to self-heal, and the ability to maintain their properties for long time periods [2; 7; 8; 9; 10]. Bentonite and bentonite-like clays possess the complete set of required properties as natural and clayy materials that are capable of swelling. Precisely because of these properties, bentonite has been chosen as a barrier material in national programs in Sweden and Finland considering the option of HLW disposal in fractured rock sites (granite massif) [11; 12; 13]. Generally, the basic protective functions of an RW repository are retention and deceleration. Retention is defined as complete waste isolation. Meanwhile, the function of deceleration serves to decrease the rate of leak propagation in the event of the loss of tightness. The protective functions of a barrier include how it contributes to the retention and deceleration of radionuclide migration and may be defined on the assumption of understanding the component properties and long-term alternation of EBS. For this, it is necessary to carry out not only laboratory but also full-scale experiments under close-to-real conditions--those that exist in repositories/disposal sites, that is, in an underground research laboratory (URL). Currently, under the auspices of the State Atomic Energy Corporation ROSATOM in Russia, work is underway to create a URL in crystalline rocks at the Yeniseisky site (Krasnoyarsk Territory). This work includes the implementation of experiments to assess the safety of creating DGRs [14]. The properties of the bentonite barrier in general are determined mainly by the characteristics of the structure of the rock-forming mineral from the smectite group--montmorillonite. At the same time, the changes in the properties of bentonite under DGR conditions are largely determined by the transformation of montmorillonite at an elevated temperature in the presence of pore water of the crystalline massif, as well as by its interaction with other EBS components (concrete, metal containers, and glass-like matrices of radioactive waste).