Thermal-hydraulic analysis of sequential disposal scenarios in a spent nuclear fuel repository

Abstract

In order to address issues related to Spent Nuclear Fuel (SNF), nations using nuclear energy have considered disposal of SNF in a Deep Geological Repository (DGR) located 500m below ground as most promising option. The Korean government has considered the multi-barrier disposal concept developed by Finland and Sweden and has developed a Korean Reference disposal System (KRS). The main consideration of KRS is how effectively it can isolate SNF from ecosystem, including considerations for thermal, mechanical and material degradations such as illitization of bentonite and canister corrosion. Among these criteria, temperature plays a significant role in maintaining repository integrity, influencing both mechanical and material degradation behavior. Consequently, various trials, including analytical and numerical solutions, have been employed to estimate temperature evolutions. However, a significant temperature difference between the analytical and numerical solutions arises due to the simulation region. Specifically, the analytical solution considers a multi-canister geometry, while current numerical solutions only account for a single-canister due to computational cost. As a result, the single canister model does not accurately reflect heat flux from the adjacent canisters. In this study, a quantitative comparison between analytical and numerical solutions using multi-canister geometries was conducted, and the results showed that the analytical and numerical solutions exhibit similar results. Additionally, four different SNF disposal methods were investigated to identify the optimized disposal method in terms of peak temperature. According to the results, it is suggested that the plop-plop method is the optimized disposal method.