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 SiO₂, 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 ⁹⁰Sr 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 ⁹⁰Sr 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 ⁹⁰Sr and Pu in these particles. ⁹⁰Sr and Pu quantification in radioactive particles showed that the ⁹⁰Sr/¹³⁷Cs radioactivity ratio (corrected to March 11, 2011) aligned with core temperature expectations. However, the ^239+240Pu/¹³⁷Cs activity ratio indicated nonvolatile Pu introduction, possibly through fuel fragments. Analyzing ⁹⁰Sr and Pu enhances our understanding of the Fukushima Daiichi accident. Deviations in ^239+240Pu/¹³⁷Cs 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.