The monograph presents the authors research results on a problem of potential impact of underground radiation-hazardous objects (module small nuclear power plant and an object of final disposal of spent nuclear fuel, Bilibinskaya NPP) under cryolithic zone conditions. The authors consider a task of assessment of thermal impact of the facilities mentioned above on country permafrost rock mass under standard exploitation conditions with taking into account the “ice-water” phase transfer and climatic particularities of the regions intended for potential dislocation of such facilities.Radioecological consequences of underground location of small NPP modules have been preliminary assessed for population and environment during standard exploitation and in a case of atmospheric emission as a result of a beyond-project accident. The authors hope that the monograph will be useful as for specialists in the area of ecological aspects of underground radiation-hazardous facilities safety, so for beginning researchers from the natural science faculties.