Long-term interaction between liner and claystone around a storage cavern

Project Description

This project included feasibility studies to analyze building a radioactive waste repository set deep within a claystone layer. Itasca was asked to estimate the potential damage and consequences that may occur in the claystone surrounding a disposal gallery.

Itasca's Role

Excavating claystone produces a specific pattern of fractures which were introduced explicitly in the model. After a long period of creep, the lining of the cavity will eventually fail. This results in further extension of the damage zone in the claystone surrounding the cavity.

The 3D model is built in parallel using FLAC3D (continuum) and 3DEC (discrete) — Figure 1. The Excavation Damaged Zone is introduced explicitly by joint elements in 3DEC and by a region of reduced Young’s modulus in FLAC3D. The assigned constitutive model allows for the simulation of short‐term behavior (Hoek‐Brown model) and long‐term behavior (Lemaitre creep law) of the claystone. The liner and canisters (Figure 2) are simulated by a strain‐softening Mohr‐Coulomb model. After excavation, the model performs six months of creep, And the liner and canisters are installed thereafter. Creep then is simulated over a period of 100 000 years. Figure 3 shows the evolution of average pressure applied by the claystone on the liner over time, while Figure 4 illustrates the plastic shear strains on the liner and canisters.

Project Results

• Results remain similar between the two models in terms of average pressure evolution on liner and of shear band formation on the liner and canisters, although the EDZ is represented using different approaches.
• The FLAC3D model shows that the void between canisters remains opened at the end of the simulation.
• The previous void is closed in the 3DEC model, yielding higher residual pressures on the liner over an extended period of time.