==Abstract==

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In 2011, Tohoku earthquake and subsequent tsunami hit Fukushima Daiichi Nuclear Power

Plant, and they lead to Fukushima nuclear disaster. For more than a decade after the disaster, concrete

materials in submerged structures of nuclear power plants have been chronically in contact with water

and resulted in calcium leaching. To assess the alteration of the concrete property, it’s necessary to

evaluate the permeability change due to calcium leaching and its effect on radioactive ion diffusion. In

this study, small scale cylindrical cement paste specimens with 3mm in diameter and 6mm in height

were prepared with water to cement ratios of 0.5 and 0.6 respectively, and they were tested in the static

leaching. Specimens were subjected to carbonation before immersed into deionized water for different

periods. CT image of each specimen at a resolution of 2.46μm/voxel was acquired in SPring-8, Hyogo,

Japan. Combining CT images and X-ray diffraction data, dissolution front of portlandite under different

leaching periods was determined, and the time dependent development law of dissolution front was

evaluated. Introducing Buil’s model as a local equilibrium, time and position dependent porosity of

cement paste due to leaching was calculated and correspondingly diffusion coefficient of Sr ion in the

numerical simulation was modified. Simulative results on Sr ion diffusivity for 10-year showed the

impact of carbonation followed by leaching on radioactive ion diffusion.

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