Patent ID: 8647015

Claim:
An artificial multi-barrier for a radioactive waste treatment facility wherein a low diffusion layer consisting of cement-based material is arranged on the outside of a concrete pit housing radioactive waste, and a low water-permeability layer provided in the form of a compacted layer consisting of a mixture of sodium-type bentonite and sand at 10 to 70% by weight of said bentonite, said sand having a grain diameter of maximally 1.2 mm or less and further containing sodium bicarbonate or sodium carbonate so as to obtain a dry density of 1.6 g/cm 3 or above and permeability of 1.0×10 −12 -m/s or below is arranged in contact with the outside of said low diffusion layer, said artificial multi-barrier being characterized by providing mixing the sodium bicarbonate or sodium carbonate with constituents of said low water-permeability layer so that in case of the leaching-out of calcium ions from the cement-based material of said low diffusion layer, said calcium ions are made to react with the sodium bicarbonate or sodium carbonate mixed with the constituents of said low water-permeability layer so that a calcium ion-diffusion barrier layer having calcium carbonate as its main component is formed in the vicinity of the interface between said low diffusion layer and said low water-permeability layer, wherein a back-filling layer consisting of refilling material having excavated earth and sand as its main component and permitting cement to be held therein is arranged in contact with the outside of said low water-permeability layer so that in case of the leaching-out of calcium ions from said back-filling layer, said calcium ions are made to react with the sodium bicarbonate or sodium carbonate mixed with the constituents of said low water-permeability layer so that a barrier layer having calcium carbonate as its main component is formed also in the vicinity of the interface between said low water-permeability layer and said back-filling layer, and wherein only a layer of said low water-permeability layer in the vicinity of the interface between said low water-permeability layer and said low diffusion layer and/or said back-filling layer comprises sodium bicarbonate or sodium carbonate of a high concentration or supersaturation concentration, while an inner layer or layers thereof comprises no sodium bicarbonate or sodium carbonate or otherwise have it of a lower concentration.