Inner and outer safety barriers are constructed when decommissioning nuclear fuel cycle facilities takes place. Combination of different barriers prevents leakage of radionuclides and other pollutants into environment.
The outer barriers formation in geological media is carried out by injection method that allows one to minimize significance of hosting rocks contribution for depositories development. Injected polymer Si-Al compounds which serve as barrier material are to meet special requirements namely low viscosity in wide temperature range, high permeability, low sensitivity to dilution, low viscosity during sol-gel process, adjustable time of gel-formation. Proposed gel-forming composition consists of liquid glass, polymer current agent and modifier. Liquid glass being a main constitution component provides strong binding to hosting rocks. In its turn polymer current agent provides gel structure strengthening and improvement of adhesion to rocks. Modifier determines sorption properties. Developed composition possesses gel-formation time of 17 hours, distribution coefficient for actinides reaches 3·10^4 cm^3/g. Mixture of grouted sand with this composition has filtration magnitude 10^(-3) – 10^(-4) m per day. Such barrier allows to prevent spread of radionuclides and nitrate-ions, that is confirmed by the results of calculations and five-year monitoring.
Permeable reactive barriers (PRB) appear for outer safety barriers as well. PRB allows in situ treatment of groundwater using a reactive material that adsorbs, decomposes and removes contaminants. Different materials can be used for creation of complex multi-layer PRB. In this study sorption characteristics of apatite, vermiculite, lightweight expanded clay aggregate (LECA), wood sawdust, perlite, natural zeolite (TREYD) and shungite were specified. Distribution coefficient (Kd) for Cs-137, Sr-90, U-238, Pu-239, Am-241, Tc-99 and stable Cr(VI) were obtained. Speciations of these radionuclides on materials were investigated using the method of sequential extraction.