In a nuclear facility, concrete materials are widely used as building structure and shielding material. Radioactive material can contaminate nearby concrete during operational period. Estimation of the radioactive level at nuclear facility is required to set up the decommission schedule with respect to the facility access guideline. Realistic radioactivity estimation model for concrete contamination is required to make decontamination schedule based on ALARA and to reduce the dose level of occupational worker.
Humidity around the concrete structure can make the moisture distribution within the concrete. Moisture content of the structure will change due to the diffusion process with time. Radioactive material on the surface of concrete will eventually diffuse into the porous concrete and contaminates the internal region of the concrete.
In this study, we have assumed two different diffusion processes depending on the different moisture content. One is for slow diffusion process near the surface and the other is for fast diffusion process in deep region. We have developed the mathematical diffusion model for the two different diffusion regions and the corresponding analytic solutions for the two regions are obtained.
Most of the contaminant of concrete is concentrated near the surface and average diffusion distance into concrete is turned out to be around 100mm. With the two different regions, radioactive contaminant can diffuse into concrete over several centimeters depending on the surface contamination level and characteristics of concrete.
With more realistic data with respect to the diffusion phenomena, extension of this model could be utilized to help the safe management of decontamination and decommissioning (D&D).