2010:25 Modelling Coupled Processes in the Evolution of Repository Engineered Barrier Systems using QPAC-EBS

Currently in Sweden, the SR-Site safety assessment for a spent nuclear fuel repository is being developed by the Swedish Nuclear Fuel and Waste Management Company (SKB). The planned SSM review of this work requires access to a sufficient modelling capability to assess the combined performance of the engineered barriers (spent fuel canister, buffer and backfill) and the natural geosphere barrier. For the integrated safety assessment, capturing the interactions in between the both natural and engineered barriers is essential for evaluation of the containment phase and this usually requires a relatively large degree of simplification in the treatment of the individual barriers. Independent modelling capability can be used to check if key safety assessment results can be reproduced. Other types of implementation involve exploration of alternative conceptual models (ACMs), as well as parameters sensitivity evaluation and uncertainty analysis. A feasible approach for the handling of such issues is reported here (based on the QPAC-EBS modelling tool).

The purpose of this project is to provide a brief summary of recent efforts to implement the QPAC-EBS code for evaluating different issues connected to the KBS-3 repository concept in Swedish granitic bedrock. This should give a rough idea of both the capabilities and the limitations of this code. Part of this work has been carried out within the now completed EU THERESA project.

This report contains a range of modelling results from simplified performance evaluation of the KBS-3 repository concept. Example of important issues in which both the natural and engineered barriers are considered include the corrosion of copper canisters, possible erosion of buffer and backfill due to the infiltration of dilute glacial meltwaters, the resaturation of buffer, backfill and geosphere, and the thermal evolution of different components in the repository (mainly due to the residual heat from the spent fuel). It should be noted that results reported here are only illustrative and are only intended for evaluation of modelling capability.