Clay Hydration, Drying, and Cracking in Nuclear Waste Repositories

The design of geologic repositories for high-level waste (HLW) and spent nuclear fuel (SNF) remains an incompletely resolved question in the nuclear fuel cycle despite significant advances over the last several decades. A key theme in current designs is the multibarrier concept, whereby several layers of barrier materials, from canisters to EBS to low-permeability host rock, ensure the isolation of the waste. An important role is played by the Engineered Barrier System (EBS), which must maintain adequate sealing capacity (i.e., low hydraulic permeability, mechanical integrity) around the waste canisters for durations of thousands of years while exposed to (i) large thermal gradients caused by heat released by the waste; (ii) large geochemical gradients due to corrosion and ion-exchange reactions at the canister-EBS and EBS-host rock interfaces; and (iii) large geomechanical gradients driven by capillary stresses associated with the initial EBS rehydration, water evaporation and, later, with the possible generation of gases at the canister-EBS interface through corrosion and hydrolysis reactions. The objective of this project is to develop a new multi-scale simulation approach to predict the coupled thermal-hydrologic-mechanical-chemical (THMC) evolution of an engineered clay barrier in the near field of a geological repository for HLW and SNF.