LASGIT (Large-scale gas injection test): experiments in gas transport testing

Figure 1. The LASGIT test site 420m below ground level showing the position of the deposition borehole, gas laboratory, pressure relief holes and instrumentation

Experiments at the Äspö Hard Rock Laboratory in Sweden are being undertaken to investigate the processes controlling fluid flow via a nuclear waste repository under deep geological conditions. The study has been carried out in collaboration with SKB (Stockholm) and with additional funding from the EURATOM 6th and 7th Framework Programmes.

LASGIT and instrumentation

LASGIT is a full-scale field experiment located 420 m below ground level at the Äspö laboratory. The laboratory design involves placement of copper/steel canisters containing spent nuclear fuel in large-diameter disposal boreholes drilled into the floor of the repository tunnels. Spaces around each canister are filled with pre-compacted bentonite blocks which over time, swell with water and reduce any construction gaps. Once hydrated, the bentonite will act as a low-permeability barrier to fluid flow from the waste canisters.

In the LASGIT experiment, a full-scale waste canister has been modified to provide points for gas injection to simulate canister defects. The borehole, bentonite and canister are fully instrumented to monitor stress, porewater pressure and relative humidity. Additional monitoring includes temperature, relative displacement of the borehole lid and anchor restraining forces. The state-of-the-art experimental monitoring and control systems for LASGIT are housed in the 'gas laboratory', a self-contained, temperature-controlled unit, designed and assembled by BGS and housed in a modified shipping container. The system can be operated and monitored remotely from any internet-connected PC worldwide.

Testing

The LASGIT experiment has involved three investigation phases: an installation phase which took place between 2003 and 2005, a hydration phase, started in 2005 and designed to hydrate the bentonite buffer, and a subsequent gas-injection phase. Two sets of gas injection tests have been carried out over a three-year period. These aim to:

  • assess processes controlling gas movement
  • examine upscaling effects on gas transport and buffer performance
  • provide test data to validate modelling approaches

Tests are ongoing. Results so far indicate that the bentonite buffer is not yet completely hydrated and that stress fields within the clay are heterogeneous. Initial results suggest that pathway dilation in the buffer is the principal mechanism governing gas transport. The coupling between gas, stress and porewater pressure will be investigated in future tests at the experimental site.

Further information

Cuss, R J, Harrington, J F, Noy, D J, Wikman, A and Sellin, P. 2010. Large scale gas injection test (Lasgit): results from two gas injection tests.

Contact

Please contact Dr Rob Cuss for further information