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

The Fukushima Daiichi Nuclear Power Plant accident released considerable radionuclides into the environment. Radioactive particles, composed mainly of SiO 2 , emerged as distinctive features, revealing insights into the accident's dynamics. While studies extensively focused on high-volatile radionuclides like Cs, investigations into low-volatile nuclides such as 90 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 90 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 90 Sr and Pu in these particles. 90 Sr and Pu quantification in radioactive particles showed that the 90 Sr/ 137 Cs radioactivity ratio (corrected to March 11, 2011) aligned with core temperature expectations. However, the 239+240 Pu/ 137 Cs activity ratio indicated nonvolatile Pu introduction, possibly through fuel fragments. Analyzing 90 Sr and Pu enhances our understanding of the Fukushima Daiichi accident. Deviations in 239+240 Pu/ 137 Cs activity ratios underscore nonvolatile processes, emphasizing the accident's complexity. Future research should expand this data set for a more comprehensive understanding of the accident's nuances.