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Isotopic Evidence of Plutonium Release Into the Environment From the Fukushima DNPP Accident

Isotopic Evidence of Plutonium Release Into the Environment From the Fukushima DNPP Accident

Jian Zheng et al. Sci Rep.

Abstract

The Fukushima Daiichi nuclear power plant (DNPP) accident caused massive releases of radioactivity into the environment. The released highly volatile fission products, such as (129m)Te, (131)I, (134)Cs, (136)Cs and (137)Cs were found to be widely distributed in Fukushima and its adjacent prefectures in eastern Japan. However, the release of non-volatile actinides, in particular, Pu isotopes remains uncertain almost one year after the accident. Here we report the isotopic evidence for the release of Pu into the atmosphere and deposition on the ground in northwest and south of the Fukushima DNPP in the 20-30 km zones. The high activity ratio of (241)Pu/(239+240)Pu (> 100) from the Fukushima DNPP accident highlights the need for long-term (241)Pu dose assessment, and the ingrowth of (241)Am. The results are important for the estimation of reactor damage and have significant implication in the strategy of decontamination.

Figures

Figure 1
Figure 1. Map showing the locations of soil sampling sites.
Figure 2
Figure 2. Mixing plot of 241Pu/239Pu atom ratio vs. 240Pu/239Pu atom ratio for litter and surface soil samples collected in the 20-30 km zones of Fukushima prefecture, Japan, and a comparison of isotopic composition with those of the Chernobyl accident and the global fallout sources.
Error bars are ± 1 standard deviation. Data on the Chernobyl accident are cited from Muramatsu et al. and Ketterer et al.. Data on the global fallout are cited from Kelley et al.. Data on atmospheric fallout in Japan are cited from Zhang et al.; these data were obtained from atmospheric fallout reference material prepared from samples collected at 14 stations through Japan in 1963-1979 by the Meteorological Research Institute (MRI), Japan.
Figure 3
Figure 3. Curves of the calculated activity ratios of 241Pu/239+240Pu and 241Am/239+240Pu from the Nagasaki atomic bomb Pu, the global fallout Pu and the Fukushima DNPP accident Pu with elapsed time.
The 241Am ingrowth from the Nagasaki atomic bomb detonation was based on the initial 241Pu/239+240Pu activity ratio estimated by Yamamoto et al.. The 241Am/239+240Pu activity ratio (0.036 ±0.006) detected in a soil core collected in Nishiyama area, Nagasaki, Japan in 2008 approached the calculated maximum value, indicating that 241Am and Pu were still together in the soils after 6 decades. 241Am from the global fallout source was expected to reach the maximum 241Am/239+240Pu activity ratio of 0.36 in the year 2042. The theoretic calculation indicated that 241Am/239+240Pu activity ratio would quickly approach the value of 1 by 7 years after the Fukushima DNPP accident and it would reach a maximum value of 3.18 in the year 2081.

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