Colloid Formation and Migration (CFM) project is being carried out within the Grimsel Test Site (GTS) Phase Ⅵ. Since 2008, the Korea Atomic Energy Research Institute (KAERI) has joined CFM to investigate the behavior of colloid-facilitated radionuclide transport in a generic Underground Research Laboratory (URL). The CFM project includes a long-term in-situ test (LIT) and an in-rock bentonite erosion test (i-BET) to assess the in-situ colloid-facilitated radionuclide transport through the bentonite erosion in the natural flow field. In the LIT experiment, radionuclide-containing compacted bentonite was equipped with a triple-packer system and then positioned at the borehole in the shear zone. It was observed that colloid transport was limited owing to the low swelling pressure and low hydraulic conductivity. Therefore, a postmortem analysis is being conducted to estimate the partial migration and diffusion of radionuclides. The i-BET experiment, that focuses more on bentonite erosion, was newly designed to assess colloid formation in another flow field. The i-BET experiment started with the placement of compacted bentonite rings in the double-packer system, and the hydraulic parameters and bentonite erosion have been monitored since December 2018.

1. Introduction
2. Research Status of CFM
3. Long-term In-situ Test
    3.1 Overview
    3.2 Experimental Layouts
    3.3 In-situ Monitoring
    3.4 Ongoing Step in LIT
4. in-rock Bentonite Erosion Test (i-BET)
    4.1 Overview
    4.2 Experiment Layouts
    4.3 Ongoing Step
5. Concluding Remarks
Acknowledgements
Declaration of competing interest
REFERENCES

• Sang-Ho Lee(Korea Atomic Energy Research Institute) Corresponding Author
• Jin-Seok Kim(Korea Atomic Energy Research Institute)
• Bong-Ju Kim(Korea Atomic Energy Research Institute)
• Jae-Kwang Lee(Korea Atomic Energy Research Institute)
• Seung Yeop Lee(Korea Atomic Energy Research Institute)
• Jang-Soon Kwon(Korea Atomic Energy Research Institute)