Quantitative evaluation of long-term state changes of contaminated reinforced concrete considering the actual environments for rational disposal (Contract research). FY2022 Nuclear Energy Science & Technology and Human Resource Development Project

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to 'the Project') in FY2022. Among the adopted proposals in FY2020, this report summarizes the research results of the 'Quantitative evaluation of long-term state changes of contaminated reinforced concrete considering the actual environments for rational disposal' conducted from FY2020 to FY2022. Estimating waste volume and concentration is essential for decommissioning concrete structures at the Fukushima Daiichi Nuclear Power Station. This study aims to quantitatively predict the distribution of contaminants in concrete components considering the actual contamination affected by the materials used (cement type, aggregate); conditions (cracking, drying/carbonation); and contact procedure with radionuclides (mixing of cooling water and seawater, changes in its concentration). Data on deformation and water movement caused by drying and reabsorption were obtained to reproduce aged concrete conditions in numerical analysis. In parallel, a numerical code was developed to calculate the distribution of cracks using a rigid-body spring model considering the history of temperature, water, and stress conditions. To evaluate the long-term penetration of radionuclides, the sorption of Cs and Sr in C-A-S-H was measured, and a multi-element transfer model considering thermodynamic phase equilibrium was developed for radionuclide penetration. Simultaneously, the penetration behaviors of Cs and Sr under the assumed conditions mentioned above were measured by autoradiography. The depth of α-nuclides penetration was evaluated by immersing specimens simulating cracks in the solution containing α-nuclides. Finally, the amount of contaminated cracked dried concrete by Cs and Sr was estimated based on the findings. (J.P.N.)