www.grimsel.com

 FZK-INE (BMWi Bundesministerium für Wirtschaft und Arbeit), Germany

 Japan Atomic Energy Agency (JAEA), Japan

Swedish Nuclear Fuel and Wast Management Co. (SKB), Sweden

 Central Research Institute of Electric Power Industry (CRIEPI), Japan

 Korea Atomic Energy Research Institute (KAERI), Korea

 POSIVA, Finland

 Nagra, Switzerland

The Colloid Formation and Migration project is dedicated to study :

• Colloid formation/bentonite erosion
• Groundwater/porewater mixing zone
• Colloid migration (filtration)
• Colloid associated RN transport

Expected Outputs

• Significant increase in the understanding of processes related to colloid formation at the bentonite/host rock interface
• Provide PA relevant information on the influence of colloids on radionuclide migration and retardation
• Gain experience in long term monitoring for repository surveillance

Colloids

Studies of natural colloids in deep groundwaters from widely ranging environments (eg Yucca Mountain, Wellenberg, Schwarzwald, Oklo, Cigar Lake etc) have been ongoing for several decades. In addition, laboratory programmes on colloid generation, stability and classical batch experiments studying radionuclide uptake on colloids (and the possibilities of subsequent release) have been reported and a significant database already exists.

It is generally accepted that five requirements must be fulfilled (the so-called colloid ladder, see below) to prove that colloid-facilitated transport of radionuclides in a potential repository host rock may be of significance to the long-term performance of a waste repository:

As has been noted in several studies (including the recently completed CRR, Colloid and Radionuclide Retardation, project in the Grimsel Test Site (GTS)), the answer to the first four questions above is probably affirmative However, before any statements can be made about the likelihood of significant colloid-facilitated radionuclide transport in the vicinity of a deep geological waste repository, two points must be addressed:

1. first, the last question about the extent of irreversibility of radionuclide-colloid associations must be investigated (it could, for example, vary for different types of colloids)
    
2. second, this, and the other processes defined in the colloid ladder, must be investigated in repository-relevant systems. Although the in situ work carried out to date has been on a longer temporal and spatial scale than is normally possible in laboratory experiments, the groundwater flow velocities are 104 - 108 times greater than would be expected in a suitable repository host rock. This is common in in situ work ongoing around the world today and is simply a question of practicalities (i.e. conducting in situ experiments within reasonable timescales and budgets). Nevertheless, it could be argued that process and mechanism understanding has now progressed to the stage where such unrealistic experiments can provide little more relevant information and that future work must consider significantly longer time scales than has been the case so far and focus on, for example, semi-stagnant groundwater systems, to better match the conditions in and around a waste repository.

For more information please contact : Ingo Blechshcmidt

Colloid Formation and Migration Experiment