In order to enhance the safety of geological disposal and the reliability of the safety assessment carried out for each stage of the geological disposal project, an assessment methodology focused on a sensitivity analysis and an evaluation of importance, which incorporates “system understanding” and “information feedback” into the existing assessment approach, has been developed in this study. In this paper, the assessment methodology and the assessment results as applied for the transuranic (TRU) waste disposal system in Japan will be described. In the sensitivity analysis, an approximate analytical solution was used in order to understand the response characteristics of the engineered barrier system (EBS). In the importance evaluation, important factors relating to the robustness of system safety were identified based on the response characteristics. Furthermore, important features, events, and processes (FEPs) related to such factors and high-impact scenarios were identified based on the information accumulated through “system understanding” and “information feedback”. Based on this approach, the robustness of the TRU waste disposal system was assessed and measures for improving the robustness were identified.
Bentonite is not thermodynamically compatible with the cementitious materials that will be present in the repository. However, the evolution of the bentonite buffer, induced by high-pH plumes originating from the cement-water reactions, occurs over very long time-scales. The kinetics of bentonite dissolution is a key feature to determine if the use of cement results in significant alteration of the bentonite buffer.To address this issue, a series of simulations were carried out using a reactive solute transport model. The code used in this study fully couples geochemical reactions, flow and transport, without splitting these processes, which can
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