The full-scale emplacement experiment (FE experiment) at the Mont Terri Underground Rock Laboratory was designed to replicate the emplacement tunnel of Nagra’s reference repository design at 1:1 scale. The objectives of the experiment are (Nagra, 2019):
To investigate Spent Fuel / High Level Waste repository-induced THM coupled effects of the host rock at full scale and to validate existing coupled THM models.
To verify the technical feasibility of constructing an emplacement tunnel using standard industrial equipment.
To optimise the bentonite buffer material design and production, in particular to produce bentonite blocks that are capable of resisting the ambient conditions during the emplacement and operation phases.
To investigate (horizontal) canister and buffer emplacement procedures for underground conditions.
To fulfil these objectives, the FE tunnel was excavated between November 2010 and May 2011, and following a ventilation period, three heaters (simulant waste canisters) were installed in the FE tunnel during 2014. The heaters sit on pedestals made of bentonite blocks and the remainder of the tunnel is filled with a granular bentonite mixture (Figure 1).
The objectives of the tasks are to model the THM processes in the Opalinus Clay, shotcrete and bentonite backfill at the Full-Scale Emplacement (FE) heater experiment. The focus will be to understand pore pressure development in the Opalinus Clay and how this is affected by heating, engineering factors (e.g. shotcrete, tunnel shape) and damage due to tunnel construction and thermal effects.
A large dataset from the FE experiment is available including time series data from construction of the tunnel, ventilation of the tunnel and the on-going heating phase (Figure 2). Data includes values of temperatures, pore pressure, relative humidity, displacement and inclination. The experiment is a full-scale representation of a waste disposal tunnel. Continuous time series data are available from prior to tunnel construction to the present day, which is currently 7 years.
The task is divided into three steps:
Benchmarking of the models against some simple, tightly defined test cases (Figure 3).
Modelling the change in pore pressure in the Opalinus Clay as a result of heating in the FE experiment. This will require 3D THM simulations with representation of partially saturated conditions.
Modelling of absolute pressures in the Opalinus Clay, which will require representation of the ventilation of the FE tunnel prior to heating. Modelling teams can choose the complexity of the representation of excavation and EDZ development.
If good progress of the first 3 steps can be achieved an additional Step 3 is planned covering options such as consideration of more realistic geometries / additional materials or the analysis of experiments on temperature dependent geomechanical properties.
The following organisations are participating in the task: