[3M09-13] Material

2:45 PM - 3:00 PM JST(5:45 AM - 6:00 AM UTC)

[3M09] Study on Elucidation of the Mechanism of Concrete Contamination by Radioactive Substances and Estimation of Contamination Distribution (27)Contribution of Cement Neutralization and Aggregates to the Contamination of Actual Concrete Due to the Fukushima Daiichi Nuclear Power Plant Accident Based on Contamination Analysis

*Kazuo Yamada¹, Hiroyuki Arai¹, Ippei Maruyama², Kazutoshi Shibuya³, Kazuto Endo¹ (1. NIES, 2. U Tokyo, 3. Taiheiyo Consultant)

Keywords:

Concrete,Contamination,Neutrallization,Aggregate,Changes over time

In the decommissioning process of the Fukushima Daiichi Nuclear Power Plant (1F), it is necessary to dismantle the building concrete, which should be carried out considering decontamination, storage, treatment and disposal. To contribute to this activity, contamination assessments of actual structures near 1F were conducted. Surface dose rate measured in January 2024 showed half values compared to December 2015 and (corrected for attenuation due to radioactive decay of Cs-137). It is possible that Cs-137 was washed away by rainwater. To confirm the penetration status, cores were collected, and the penetration cross-sections were evaluated by imaging plates. Cs-137 was concentrated in the surface neutralized area, and it was difficult to evaluate penetration into the unneutralized area. Cs-137 were uniformly detected in certain aggregates. The concentration of Cs-137was higher in the aggregates, indicating that the aggregates are an important contributor to the radioactive contamination of the concrete. It was also confirmed that Cs-137 does not migrate in closed indoor storage.