Conceptual model of source-term assessment with the concrete degradation of engineered barrier

Radionuclide mobilization and subsequent release from waste package is initiated by water contact after the cover and vault materials allow movement of water into the vault. Failure usually will occur gradually, which results in water percolating into the waste form at a rate gradually increasing with time. To model this gradual failure process, several assumptions are needed that 1) flow through the disposal facility is uniformly distributed and steady, 2) at the time of closure, the combination of cover and vault functions as a perfect barrier to flow, and that this condition will persist for a relatively short time, 3) between the beginning of failure and the completion of failure, the system comprising vault and cover is permeable to flow, and the permeability increases with time. This hydraulic evolution is described by a function produced using the 4SIGHT code. That function is expected to be approximated by a series of steps for a linear function. Eventually, the flow rate reaches the ambient infiltration rate. In this conceptual model, three modes of dissolution are considered such as instant dissolution, congruent dissolution and diffusional release