Identification of plutonium isotopes in insoluble particles released by the accident of Fukushima Daiichi Nuclear Power Plant

Igarashi, Junya*; Zheng, J.*; Zhang, Z.*; Ninomiya, Kazuhiko*; Satou, Yukihiko   ; Fukuda, Miho*; Ni, Y.*; Aono, Tatsuo*; Shinohara, Atsushi*

Plutonium is one of the most notable radionuclides in the nuclear accident. The amounts of Pu released by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident were investigated so far. However, the existence of Pu isotopes from the global fallout makes it difficult to accurately assessment of Pu contamination by the FDNPP accident. To avoid this problem, identification of Pu contamination source from the Pu isotopic ratios is important. However, various ratios have been reported by the researches due to the contamination from global fallout. In this work, we focused on the insoluble radioactive Cs particles made of mainly SiO (insoluble particles) released from the FDNPP to determine accurate Pu isotopic ratios. Due to its insolubility, the particles retained the original property at the time of emission from the reactor. Therefore, the insoluble particles are considered to be free from the contamination of global fallout. In addition, the amounts of Pu in the insoluble particles provide the information about their formation process in the reactor. In this study, we identified Pu isotopes in insoluble particles by radioactive analysis and ICP-MS measurement. The isotopic ratios of Pu/Pu and Pu/Pu were determined as 0.330-0.415 and 0.162-0.178, respectively and activity ratio of Pu/Cs was about 10 in each particle.