Speaker
Description
Currently proposed concepts for safe isolation of radioactive wastes imply development of a multibarrier system which consists of both natural and engineered barriers. Hosting rock of depository serves as a natural barrier. It appears for already-existing depositories and disposal facilities. It is naturally chosen on the stage of disposal development. Vertical and horizontal curtains of polymeric materials, clay back filling, slurry-type walls appear for engineered barrier. It serves as impervious barriers for filtration prevention. Besides there is another type of engineered barrier for prevention of contaminants migration it consists of both organic and inorganic sorbents, biosorbents etc.
Technology of inner barriers creation is determined by both geometric parameters of repository and species of solid or solidified radioactive waste will have been placed therein. Nowdays Russian Federation has the experience of constructing an inner safety barrier system namely when industrial uranium-graphite reactor (PUGR) decommissioning. As barrier material one used a mixture of three components: kaolinite (Kampanovskoye deposit), bentonite (Khakass deposit), vermiculite (Tatar deposit). It was a composition design what reveals high sorption activity being cost effective. Besides chosen fractional composition possessed quite high index of powder flowability. The total volume of involved barrier material amounted more than 40 thousand m^3.
Another type of inner barrier was developed for reactor storage of solid waste. This type of storage presumes a hodgepodge of solid radioactive wastes of irregular shapes made of graphite, metal, organic compound and so on. In this case clay suspension in gel (thick slurry) was offered to play a role of barrier materials, which was injected into storage room. Such hind of barriers has high penetrability and prevents migration of radionuclides. Clays from the local depository near Tomsk (Kornilovo) were chosen as a component of barrier material along with the mixture of clays which was either used as back filling for reactor. Optimal solid-liquid ratio was 2:1. Large-scale experiments confirmed the possibility of storage room full filling without any cavities left.
The developed approaches to inner safety barriers construction allow researches to choose the appropriate technology of their creation depending on the type of the object and its technical features.
