Fukushima Daiichi Nuclear Power Plant Accident; Understanding Formation Mechanism of Radioactive Particles through Sr and Pu Quantities

福島第一原子力発電所事故; Sr及びPu量による放射性粒子の形成メカニズムの理解

五十嵐 淳哉*; 二宮 和彦*; Zheng, J.*; Zhang, Z. J.*; 福田 美保*; 青野 辰雄*; 箕輪 はるか*; Yoshikawa, Hideki*; 末木 啓介*; 佐藤 志彦   ; 篠原 厚*

Igarashi, Junya*; Ninomiya, Kazuhiko*; Zheng, J.*; Zhang, Z. J.*; Fukuda, Miho*; Aono, Tatsuo*; Minowa, Haruka*; Yoshikawa, Hideki*; Sueki, Keisuke*; Satou, Yukihiko; Shinohara, Atsushi*

The Fukushima Daiichi Nuclear Power Plant accident released considerable radionuclides into the environment. Radioactive particles, composed mainly of SiO, emerged as distinctive features, revealing insights into accident's dynamics. While studies extensively focused on high-volatile radionuclides like Cs, investigations into low-volatile nuclides such as Sr and Pu remain limited. Understanding their abundance in radioactive particles is crucial for deciphering the accident's details, including reactor temperatures and injection processes. Here we aimed to determine Sr and Pu amounts in radioactive particles and provide essential data for understanding the formation processes and conditions within the reactor during the accident. We employed radiochemical analysis on nine radioactive particles and determined the amounts of Sr and Pu in these particles. Sr and Pu quantification in radioactive particles showed Sr/Cs radioactivity ratio (corrected to March 11, 2011) aligned with core temperature expectations. However, Pu/Cs activity ratio indicated non-volatile Pu introduction, possibly through fuel fragments. Analyzing Sr and Pu enhances our understanding of the Fukushima Daiichi accident. Deviations in Pu/Cs activity ratios underscore non-volatile processes, emphasizing the accident's complexity. Future research should expand this dataset for a more comprehensive understanding of the accident's nuances.