Investigation of the thermal-hydro-mechanical (THM) behavior of GMZ bentonite in the China-Mock-up test

In this paper, the large scale China-Mock-up test, intended to study the thermal-hydro-mechanical (THM) behavior of Gaomiaozi (GMZ) bentonite under relevant repository condition, is presented. In accordance with the current disposal concept of High-level Radioactive Waste (HLW) disposal in China, the facility is designed as a vertical cylindrical tank, filled with compacted GMZ-bentonite. A heater, which simulates the HLW canister, is placed inside the compacted bentonite blocks and pellets. The installed hydration system on the exterior surface simulates the supply of groundwater. The operational phase started on 1st April 2011. Based on the current recorded experimental data, several aspects are addressed in the paper, including the observed THM behavior of the compacted bentonite, the displacement of the electrical heater, and also the influence of unexpected interruptions of electric power supply. The saturation process of the compacted bentonite is strongly influenced by the competing mechanisms of drying effect induced by the heater and the wetting effect by water penetration. As a result, the desiccation–saturation process was observed in the zone close to the heater. An upward displacement of the heater was also noticed, which verified the potential influence of buffer material on the stability of canister. The experiment is a valuable step in establishing the viability of the reference concept, and making progress in the understanding of the behavior of buffer material under thermal-hydro-mechanical (THM) coupled condition.