[2H13-17] Sorption and Diffusion

5:00 PM - 5:15 PM JST(8:00 AM - 8:15 AM UTC)

[2H16] Reduction of the surface dose rate of actual contaminated concrete in the field and its mechanism

*Kazuo Yamada¹, Ippei Maruyama², Kazutoshi Shibuya³ (1. NIES, 2. UTokyo, 3. Taiheiyo Consultant)

Keywords:

concrete,contmination,decrease,cesium,ion exchange

The surface dose rates of actual concrete structures located a few tens of meters from the Pacific Ocean that were contaminated by radioactive Cs released by the Fukushima Daiichi Nuclear Power Plant accident were measured in December 2015 and January 2024, and it was found that they had halved over the eight-year period. In this study, the mechanism of this decrease was studied. The sides of the collected core were coated with epoxy resin and immersed in pure water and artificial seawater for three months. As a result, the surface dose rate hardly changed in pure water, but a few tens percentage points of decrease was observed in artificial seawater. The decrease in contamination was also confirmed by autoradiography of the core surface. Radioactivity measurements of the solution after immersion also confirmed that the seawater caused leaching, with 10 Bq/L in pure water and 150 Bq/kg in seawater. This was thought to be due to the exchange of Cs ions adsorbed with K ions in seawater. It was shown that when contaminated concrete is placed by the sea, the adsorbed radioactive Cs is affected by sea salt and there is a possibility that it will be released back into the environment.