Coupled Thermal-hydraulic-mechanical Modelling of the Canister Retrieval Test

Abstract

One of the in-situ tests chosen for examination as part of a series of numerical simulations undertaken for the Engineered Barriers Systems Task Force (EBS-TF) is the Canister Retrieval Test (CRT) carried out in the Äspö Hard Rock Laboratory. The CRT basically aims at demonstrating the practicality of recovering emplaced containers after the bentonite is fully saturated and has developed its maximum swelling pressure. The CRT also studies the thermal, hydraulic and mechanical evolution in the buffer from start until full water saturation. In the CRT, an electrically heated full-scale container is lowered into a deposition hole lined with cylindrical blocks and ring-shaped blocks of bentonite in the fall of 2000 and retrieved after five years of operation in early 2006. A large number of instruments measure pressure, temperature and other parameters during this time. Coupled thermal-hydraulic (TH) and coupled thermal-hydraulic-mechanical (THM) simulations for the CRT are conducted using the CODE_BRIGHT program in order to evaluate the effectiveness of its modelling code in matching the observed evolution of the coupled processes in unsaturated bentonite material. The measured temperatures in the bentonite materials and in the rock are well simulated except for the measurements located in bentonite bricks because of the inadequate of thermal characterization of the bentonite bricks. The simulated liquid saturation profiles at the end of the test matched the measurements very well at different layers. The simulated vertical stresses in the bentonite materials capture the trends and the value of measurements reasonably well.