The Swedish Nuclear Fuel and Waste Management Company (SKB) included analysis of a range of scenarios in its SR-Site report. SKB grouped these scenarios into two categories—main and residual. The main scenario included a likely scenario (corrosion failure) and a less probable scenario (seismicity-induced shear failure). The residual scenario included two unlikely scenarios—isostatic-load and growing pinhole failures. For each of the scenarios, SKB analysed a reference case and several variations (created by altering features and processes, and by degrading barrier components) referred to as ‘what-if” analysis cases for sensitivity and barrier function analyses.
The objective of the work reported in this Technical Note is to evaluate SKB’s what‑if analysis for reproducibility of results and identify any shortcomings by probing SKB’s modelling approach, based on what can be inferred from SKB reports and through our independent modelling. To fulfil this objective, we developed a simple model for the reference cases and selected what-if scenario cases. The what-if scenario cases we considered include (i) corrosion scenario with initial advection, (ii) corrosion scenario with faster spent nuclear fuel (SNF) degradation, (iii) growing pinhole scenario with flow in the disposal tunnels’ crown region, and (iv) growing pinhole scenario with shorter distance to the fracture−tunnel intersection. The overall goal was to develop an understanding of the repository system’s behaviour, so that we will be able to find any potential shortcomings in the SKB model and identify aspects that may have not been considered by SKB.