INVESTIGATION OF THE THM BEHAVIOUR OF THE BUFFER AND ROCK-BUFFER INTERACTION DURING THE CANISTER RETRIEVAL TEST PERFORMED IN THE ASPO HARD ROCK LABORATORY

摘要

In the framework of the THERESA European project, numerical modelling of coupled THM and THMC behaviour of buffer (bentonite) and buffer-rock interfaces for underground nuclear waste repositories have been undertaken, with focus on the performance assessments. A major step of the project was the analysis of a large scale test performed in AspS Hard Rock Laboratory, called the Canister Retrieval test. It consists in a full scale test of the emplacement of a canister with the surrounding buffer material. A deposition hole was first bored, and then the canister with heaters was installed together with bentonite blocks. The gap between the rock and the bentonite blocks was filled with pellets. The whole set was artificially wetted from its external boundary. The evolution of the THM processes was recorded over 5 years. Before analysing the whole CRT experiment, a preliminary simpler problem has been defined, which consisted in modelling a disc of buffer at canister mid-height. Thanks to the available experimental recorded measurements, it has been possible to numerically investigate the respective influence of the various THM parameters involved in the model, which is based on one hand on the Richard's approximation for the flow calculation and on the other hand on a Biot's type model for the hydro-mechanical behaviour. It has revealed the large influence of the liquid relative permeability, which is unfortunately in general not directly available from experiments. Then, in a second stage, the whole CRT experiment has been analysed. For simplicity reasons, an axisymetrical model has been adopted, although the presence of a neighbouring experiment did influence the CRT results. The comparisons of the most relevant features of the test, between predicted and measured values, are presented and discussed in the paper.