An Overview of the long-term diffusion test, Grimsel Test Site, Switzerland

Marin, A.*; Siitari-Kauppi, M.*; Havlov, V.*; Tachi, Yukio  ; Miksova, J.*

Matrix diffusion is very important in the context of the performance assessment of radioactive waste repository in the crystalline rocks. An in-situ long-term diffusion (LTD) project has been performed at the Grimsel Test Site, Switzerland, to realistically evaluate matrix diffusion of radionuclides in crystalline rock with minimal disturbance to in-situ conditions. As part of phase-I, tracers, HTO, Na-22, Cs-134, were continuously circulated through a packed-off borehole and the tracer concentrations in the solution was monitored for 2.5 years. Subsequently, the borehole section was overcored and the tracer profiles in the rock analyzed. These results were analyzed with diffusion-sorption models by different teams. The phase-II plans including experimental design and tracers selection will be discussed.