In order to determine the long term safety (over timescales up to one million years) of a radioactive waste repository, computer codes are used that run simulations over these sorts of time scales. The information used in these codes comes from relatively short term experiments (days, weeks, months). It is therefore important to be confident that the values used in the model are suitable for such long time scales.

Radionuclide transport models are used to quantify on the long term transport of radionuclides, which have escaped from a radioactive waste repository, in the rock surrounding a deep geological repository.

Whether models, calibrated with small-scale tracer tests, are suitable for large-scale transport problems relevant to a repository for radioactive waste or whether the transport parameter values determined from small-scale tests can be extrapolated to large-scale models, can only be determined using the experimental data obtained from a large-scale tracer experiment.

Background

• Modelling of groundwater flow and solute transport is important for the long-term safety analysis of a repository.
• In fractured rock, fast flow and advective dispersive transport occur in the major failure zone (fracture network); while slow diffusion and sorption in the rock mass.
• To validate conceptual models, in-situ experiments have been conducted in underground laboratories, but mainly on a small scale.
• BGR has performed a series of tracer tests in different scales at the Grimsel Test Site (1984 - 1997) to examine scale-dependent transport processes.

This is where EFP comes in, its objectives are to:

• Examine the method for characterising the rock mass and for developing a structural model,
  
  
• Test the numerical model for calculation of the temporal and spatial distribution of tracer concentration on a large-scale
  
  
• Validate the developed model using in-situ data from large-scale tracer experiments at the Grimsel Test Site (GTS).
  

Concept