A Project focusing on the contamination mechanism of concrete after the accident at Fukushima Daiichi Nuclear Power Plant

福島第一原子力発電所事故によるコンクリート汚染機構の解明

山田 一夫*; 丸山 一平*; 芳賀 和子*; 五十嵐 豪*; 粟飯原 はるか   ; 富田 さゆり*; Kiran, R.*; 大澤 紀久*; 柴田 淳広  ; 渋谷 和俊*; 井田 雅也*; 小林 佑太朗*; 駒 義和  

Yamada, Kazuo*; Maruyama, Ippei*; Haga, Kazuko*; Igarashi, Go*; Aihara, Haruka; Tomita, Sayuri*; Kiran, R.*; Osawa, Norihisa*; Shibata, Atsuhiro; Shibuya, Kazutoshi*; Ida, Masaya*; Kobayashi, Yutaro*; Koma, Yoshikazu

To properly decommission the Fukushima Daiichi Nuclear Power Plant, the contamination levels and mechanisms for the concrete structures must be assessed. In this review, we outline the results of this study and present the objectives of a future study called "Quantitative Evaluation of Contamination in Reinforced Concrete Members of Fukushima Daiichi NPP Buildings Considering the Actual Environment Histories for Legitimate Treatments", which will run from October 2020 to March 2023. The experimental results from the first project indicate that concrete carbonation, Ca leaching, and drying conditions affected the adsorption of Cs and Sr and their penetration depths. Additionally, the studies showed that -nuclides precipitated on the surface of the samples because of the high pH of concrete. A reaction transfer model was developed to further assess the adsorption characteristics of Cs and Sr in carbonated cement paste and concrete aggregates. The model used real concrete characteristics from the FDNPP materials and historical boundary conditions at the site, including radionuclide concentrations and penetration profiles within the turbine pit wall. The water suction by dried concrete was evaluated with the consideration of the structure change of cement hydrates by X-ray CR and H-NMR relaxometry. In the new project, the studies will also include concrete cracks for more realistic contamination estimations.