Presentation Retrospective investigation on soil Pu background to estimate the radiation impact of the Fukushima nuclear accident released Pu in the environment

Zheng, Jian  ,  Yang, Guosheng  ,  Tagami, Keiko  ,  Uchida, Shigeo

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident led to the release of large amounts of radionuclides into the environment. After the FDNPP accident, the release of Pu isotopes was detected in various environmental samples, and an extremely high 241Pu/239+240Pu activity ratio (> 100) was found in the released Pu, thus the radiation impact on the environment and humans has raised an increasing concern in the public and scientific community. Obtaining Pu background data in the environment is essential for contamination source identification and assessment of environmental impact of Pu released from the FDNPP accident. However, no baseline information on Pu isotopes in Fukushima Prefecture has been reported. Here we report a retrospective investigation on the distribution of Pu in surface soils to establish the Pu baseline before the accident for the estimation of radiation impact of the FDNPP accident-released Pu in the environment. We analyzed 80 surface soil samples collected from the central-eastern Japan during 1969 – 1977 for 239+240Pu activity and 240Pu/239Pu atom ratio to establish the baseline before the FDNPP accident. We found that 239+240Pu activities ranged from 0.004 –1.46 mBq g-1, and 240Pu/239Pu atom ratios varied narrowly from 0.148 to 0.229 with a mean of 0.186 ± 0.015. We also reconstructed the surface deposition density of 241Pu using the 241Pu/239Pu atom ratio in the Japanese fallout reference material. The obtained results indicated that, for the FDNPP-accident released 241Pu, a similar radiation impact can be estimated as was seen for the global fallout deposited 241Pu in the last decades. Acknowledgment: This work has been supported by the Agency for Natural Resources and Energy, the Ministry of Economy, Trade and Industry (METI), Japan, and partly supported by the Kakenhi Grant-in-Aid for Scientific Research on Innovative Areas (24110004).
国際第四紀学連合第19 回大会(INQUA 2015)

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