An Overview and key results from the long term in situ diffusion project (ltd) at the Grimsel Test Site, Switzerland

Martin, A.*; Fukatsu, Yuta  ; Tachi, Yukio  ; Ishida, Keisuke*; Muuri, E.*; Siitari-Kauppi, M.*; Havlov, V.*; Vokal, A.*

Diffusion and sorption parameters used in performance assessment calculations for assessing the long term safety of future radioactive waste repositories are typically derived from rock samples that are de-stressed once removed from the host rock. This can lead to an over-estimation of matrix diffusion and sorption from lab based experiments primarily due to sample preparation in comparison with actual conditions in crystalline rocks. Despite this, there have been very few long-term field-scale experiments to realistically evaluate matrix diffusion and sorption of radionuclides in fractured rock with minimal disturbance to in-situ conditions. These issues have formed the basis for the design of the Long Term Diffusion (LTD) project at the Grimsel Test Site (GTS) in Switzerland. The results and comparison to diffusion and sorption models, with a particular focus on scaling from lab to in situ conditions and process understanding will be overviewed in this paper.