Assessment of Radioactive Cesium Contamination in Concrete Structures near Fukushima Daiichi Nuclear Power Plant

This study investigates the contamination of concrete by radioactive cesium released by the Tokyo Electric Power Company Fukushima Daiichi Nuclear Power Plant accident using samples from various sites in the town of Okuma, Japan. Concrete contamination was effectively evaluated through surface dose rate measurements using Geiger-Müller tubes with shielding. Corresponding radioactivity concentrations were evaluated using an NaI scintillator in a low background environment. The contamination levels were considerably lower in areas shielded from rain compared with outdoor areas exposed to rain. Contamination within concrete can be primarily attributed to radioactive Cs enrichment in specific concrete aggregates and further influenced by carbonation of the cement paste. In non-carbonated sections, radioactive Cs was concentrated in aggregates near the surface, hindering the penetration of detection into the cement paste. Concrete samples subjected to rain exhibited reduced contamination over time. Thus, rain exposure, aggregate properties, and the degree of carbonation emerged as pivotal in predicting concrete contamination. Therefore, this study yields insights into on-site measurement methods, temporal contamination trends in the environment, and the distribution of contamination within concrete structures.