Distribution and impact of plutonium originating from Fukushima Daiichi Nuclear Power Plant accident in the environment: an overview of a decade studies

This study reviewed the current knowledge of plutonium (Pu) isotopic composition (the atom or activity ratios) and activities of 238Pu, 239Pu, 240Pu, and 241Pu derived from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011. In this critical review, we documented the characteristic values of Pu atom or activity ratios (fingerprints) and presented its spatial distributions around the FDNPP site. Based on multiple Pu fingerprints (238Pu/239+240Pu activity ratio, 240Pu/239Pu atom ratio, and 241Pu/239Pu atom ratio), we clarified there received the Pu contamination from the FDNPP accident in a restricted terrestrial area, while Pu in the northwest Pacific Ocean is still predominately sourced from the Pacific Proving Grounds (PPG) fallout and the global fallout. Using a simple two end–member mixing model, the contributions of Pu from the FDNPP accident were calculated to be on average 27±34% (n=149) in soils, 55±32% (n=38) in litter samples, and 67±26% (n=129) in the air dust/black substances, respectively. In the marine environment, the PPG source contributed 45±15% (n=76) in the seawaters and 42±12% (n=48) in the sediments. The spatial distribution of Pu atom or activity ratios based on existing studies suggested that: 1) the Pu contamination in the northwestern FDNPP site was mainly observed in an area within 50 km radius; 2) in the southwestern FDNPP site, the Pu contamination was mainly observed in a zone within 30 km radius. The studies of Cs-bearing radioactive particles indicated that Pu occurred as Pu oxide and the fuel fragments containing Pu were released from the reactors to the surrounding environment associated with micron-scale Cs-bearing radioactive particles. It should be noted that the fractionation between Pu and other radionuclides occurred after release. Finally, these new findings about the Pu fingerprints around the FDNPP site help us to establish a reference background database for the coming environmental risk assessment and geochemical study in this region.the 6th International Conference on Environmental Radioactivity, ENVIRA 2021: Fukushima Accident – 10 years of Environmental Investigations, and New Challenges in Environmental Radioactivity Studie