Isotopic evidence of plutonium release into the environment from the Fukushima DNPP accident

The Fukushima Daiichi nuclear power plant (DNPP) accident caused massive releases of radioactivity into the environment. The released highly volatile fission products, such as Te-129m, I-131, Cs-134, Cs-136 and Cs-137 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 Pu-241/Pu239+240 (> 100) from the Fukushima DNPP accident highlights the need for long-term Pu-241 dose assessment, and the ingrowth of Am-241. The results are important for the estimation of reactor damage and have significant implication in the strategy of decontamination.