The broad objective of the Colloid and Radionuclide
Retardation Experiment (CRR) experiment was to significantly improve understanding of the in situ retardation of colloid-associated, safety-relevant radionuclides in the vicinity of an engineered barrier/host rock interface.

This was achieved by:

• Investigation of the stability of bentonite colloids in different types of water (Grimsel groundwater and FEBEX bentonite porewater).
  
  
• Investigation of the extent of bentonite colloid formation at the EBS/host rock interface.
  
  
• Investigation of the in situ migration/retardation of bentonite colloids in fractured host rocks.
  
  
• Improving the conceptual models for colloid and colloid-mediated radionuclide transport for reactive transport modelling.
  
  
• Further development, calibration and validation of existing (transport) codes and databases for the analysis of in situ retardation of safety relevant radionuclides in association with colloids.
  
  
• Definition of the degree of transferability of model predictions and of results from laboratory experiments to the geosphere.