A simple procedure is derived for being included in the design process of the engineered barrier system of the radioactive waste disposal. This procedure is based on the steady state analytic solution of the diffusion-convection equation of the finite domain. Once the fluxes on both edge sides are assumed for each domain in the multi-layered engineered barrier, the unknown fluxes are solved as the solution of the simultaneous equation system of the steady state solution. The present procedure is very simple and stable for obtaining the fluxes and three distinct outlet boundary conditions such as natural boundary, zero concentration, and the mixing cell are formulated. The application of the procedure is readily extended for severer condition, for example, the case of the degradation of one of the layers is examined by inserting additional domains as altered regions and the result indicates the fluxes are obtained fast and soundly without difficulties.

  In radioactive waste disposal facilities, there is concern about the alteration of bentonite in an alkaline condition derived from cementitious materials. In this study, the interaction between shotcrete and pumice tuff for 15 years was investigated in order to understand the formation of secondary phases in alkaline conditions. The results showed that amorphous C-(A-)S-H with a Ca/Si ratio of about 0.7 or slightly richer in Ca and Al was formed in the range of a few mm or a few cm in contact with shotcrete, due to the dissolution of initial amorphous phases such as volcanic glass. The alkali-affected zone of pore water in the rock extends at least 9 cm from the interface, and the porosity and permeability were not changed at depths deeper than a few mm from the interface with shotcrete. It was inferred that the alkali-affected zone was determined by some factors, including groundwater advection. Based on previous findings, it is necessary to consider a transition from C-(A-)S-H to tobermorite in the alkaline alteration reaction of bentonite materials. This study suggested that the transition may take place after a decade under low-temperature conditions such as those in this study site.