Abstract
Radioactive particles were released into the environment during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Many studies have been conducted to elucidate the chemical composition of released radioactive particles in order to understand their formation process. However, whether radioactive particles contain nuclear fuel radionuclides remains to be investigated. Here, we report the first determination of Pu isotopes in radioactive particles. To determine the Pu isotopes (239Pu, 240Pu and 241Pu) in radioactive particles derived from the FDNPP accident which were free from the influence of global fallout, radiochemical analysis and inductively coupled plasma-mass spectrometry measurements were conducted. Radioactive particles derived from unit 1 and unit 2 or 3 were analyzed. For the radioactive particles derived from unit 1, activities of 239+240Pu and 241Pu were (1.70–7.06) × 10−5 Bq and (4.10–8.10) × 10−3 Bq, respectively and atom ratios of 240Pu/239Pu and 241Pu/239Pu were 0.330–0.415 and 0.162–0.178, respectively. These ratios were consistent with the simulation results from ORIGEN code and measurements from various environmental samples. In contrast, Pu was not detected in the radioactive particles derived from unit 2 or 3. The difference in Pu contents is clear evidence towards different formation processes of radioactive particles, and detailed formation processes can be investigated from Pu analysis.
Highlights
On 11 March 2011, a major earthquake of magnitude 9 occurred in eastern Japan and resulted in a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP)
In the Chernobyl accident, Muramatsu et al.[17] reported that the 240Pu/239Pu atom ratio was approximately 0.408 ± 0.003, and higher values of 0.45–0.52 were reported for Chernobyl hot particles[18]; such a high value resulted from the long burn-up time of the nuclear fuel
The detected 240Pu/239Pu ratio in the environmental samples were close to that of the fuel inventory calculated by Nishihara et al In addition, the 241Pu/239Pu atom ratio is important for identifying Pu source. 241Pu/239Pu atom ratio of global fallout was reported as 0.00194 ± 0.00014 (241Pu decay corrected to 1 January, 2000)[14]
Summary
On 11 March 2011, a major earthquake of magnitude 9 occurred in eastern Japan and resulted in a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP). After the FDNPP accident, a higher value of 241Pu/239Pu atom ratio (0.103–0.135(241Pu decay corrected to 15 March, 2011)) was reported from soil and litter samples around the FDNPP as well as 240Pu/239Pu atom ratio[21] These environmental samples were influenced by the contamination from the global fallout existing before the FDNPP accident, which hampered the accurate assessment of the environmental impact of the released Pu isotopes. After the FDNPP accident, small particles containing highly concentrated radioactive Cs (radioactive particles) were detected in various environmental samples such as air dust[30], soil[31], vegetation[32], river water[33], and dust in residences[34].
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