1. Geomechanics for nuclear waste disposal
Geomechanics plays a key role in many aspects of deep geological disposal, the favoured concept for the safe confinement of high-level nuclear waste. Deep geological disposal involves the excavation of a network of tunnels in a suitable host rock a few hundred meters below the surface. The waste is then emplaced in the tunnels themselves or in vertical boreholes drilled for this purpose. In a number of designs, the waste is surrounded by an engineered barrier made up of compacted highly swelling clay. High-lever waste is heat emitting so coupled thermo-hydro-mechanical (THM) phenomena affect the near field, i.e. the engineered barrier and immediately adjacent rock. Another important issue of the excavation works is the need to control the Excavation Damaged Zone (EDZ) that, inevitably, is generated around the openings.
A proper design of the repository requires a sound understanding, from a fundamental point of view, of the phenomena involved; empirical rules are of doubtful applicability given the very long times associated with this type of problems. Integration of this understanding and comparison with field observations entail the use of advanced numerical models incorporating coupled THM formulations. Large-scale tests performed in underground research laboratories provide the data for the validation and further improvement of the theoretical formulations, parameters and computational tools.
The main topics covered by the course are:
– Introduction. What is nuclear waste?
– Deep geological disposal of high-level nuclear waste
– Theoretical HM and THM formulations
– Constitutive models for compacted swelling clay and argillaceous rocks.
– Application to the excavation of a tunnel in argillaceous rock
– Analysis of thermal effects on argillaceous rocks
– Behaviour of an engineer barrier under THM actions
– Summary and conclusions