Colloid Formation and Migration (CFM)

For the in-situ CFM experiment, a potential source of radionuclides and colloides (with radionuclides pre-spiked bentonite rings) will be emplaced in an advective flow system in the host rock.

The formation and transport of colloids and colloid-associated radionuclides is monitored under repository relevant flow conditions and over relevant distances.

The stability of the bentonite-derived colloids and possible reversibility of radionuclide uptake onto these colloids is investigated in time scales which minimise kinetic effects.

CFM in-situ experiment – situation at the AU tunnel

The overall concept has been defined, its implementation in terms of the in-situ set-up for the CFM experiment has not yet been finalised in detail. The principle elements are:

• Sealing the shear zone at the tunnel surface with a megapacker to create a no(or low) flow boundary and to reduce the gradient in the groundwater heads from the rock towards the tunnel
• Generating a monopole flow field via a short, small-diameter borehole reaching into the shear zone near the tunnel surface
• Placing a colloid source (bentonite) into the water conducting shear zone (beyond the radius of influence of the GTS tunnel system) via a bentonite emplacement borehole

An essential requirement for the success of the experiment is the perfect seal of the tunnel surface where it is intersected by the shear zone. This requirement has been fulfilled with the megapacker.

The video above shows the concept of the transport of colloids through the shear zone.

Colloid Formation and Migration Experiment

Current CFM Project Partners

 Bundesgesellschaft für Endlagerung (BGE), Germany

 BMUKN (FSU Jena, GRS, KIT) (Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection / Karlsruhe Institute of Technology), Germany

 Korea Atomic Energy Research Institute (KAERI), Korea

 Nuclear Waste Management Organization (NUMO), Japan

Nuclear Waste Services, UK

Nagra, Switzerland

Contributors

Centro de Investigaciones Energéticas Medioambientales y Tecnológicas, (CIEMAT), Spain
Paul Scherrer Institute (PSI), Switzerland
Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), Germany
KTH Royal Institute of Technology, Not Sweden
Los Alamos National Laboratory / Earth Systems Observations (LANL), USA
University of Helsinki / Departement of Chemistry (HYRL), Finland

CFM partner meeting in Karlsruhe (Hosted by KIT/INE) 29 to 30 June 2016

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

The expected outputs by the end of the 10-year CFM project include:

• Significantly enhanced understanding of the processes related to colloid formation at the bentonite/host rock interface
• Performance-assessment relevant information concerning the influence of colloids on radionuclide migration and retardation
• Added experience in the long-term monitoring for repository surveillance purposes

The CFM project is the most recent in a series of experiments conducted within the Radionuclide Retardation Programme at the GTS which started in 1984. Of interest is the colloid-facilitated transport of radionuclides in a repository host rock. Such transport could influence the long-term performance of a deep geological repository for radioactive waste. The colloid ladder illustrates the five requirements that must be fulfilled for colloid-facilitated radionuclide transport to be significant.

Colloid ladder with the requirements for significant colloid-facilitated radionuclide transport in a deep geological repository

Recent investigations of colloid-facilitated radionuclide transport tend to address mainly two aspects of the colloid ladder:

1. The reversibility of the uptake of radionuclides onto colloids – For example does it vary with the colloid type?
2. The evolution of the associated processes in a repository-relevant system – Although much of the in-situ work conducted around the world has been on longer temporal and spatial scales than is normally possible in laboratory experiments, for reasons of practicality the groundwater velocities are typically more than 100 times greater than would be expected in a suitable repository host rock. We believe that process understanding has progressed to the stage where more realistic experiment set-ups are necessary in order to gain new insights. The aim should be to work with significantly longer time scales and to focus on, for example, semi-stagnant groundwater systems that better match the conditions in and around a waste repository.

Colloid Formation and Migration Experiment