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Geochemical Journal, Vol. 46 (No. 4), pp. 355-360, 2012

Isotopic determination of U, Pu and Cs in environmental waters following the Fukushima Daiichi Nuclear Power Plant accident

Aya Sakaguchi,1 Akinobu Kadokura,1 Peter Steier,2 Kazuya Tanaka,3 Yoshio Takahashi,1 Haruka Chiga,1 Akihito Matsushima,4 Satoru Nakashima4 and Yuichi Onda5

1Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
2VERA-Laboratory, Faculty of Physics, University of Vienna, Währinger Str. 17, A-1090 Vienna, Austria
3Institute for Sustainable Sciences and Development, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8530, Japan
4Natural Science Centre for Basic Research and Development, Hiroshima University, 1-4-2 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
5Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan

(Received January 27, 2012; Accepted June 12, 2012)

Abstract: Concentrations of the radionuclides, U, Pu, and Cs were measured in water samples (10-20 L) to study analyte dispersion and migration following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. A total of 8 water samples including oceanic water and paddy-field water were collected in the vicinity of the plant. Determinations of U, Pu and Cs isotopes were performed by accelerator mass spectrometry (AMS), inductively coupled plasma mass spectrometry (ICP-MS), and γ-ray spectrometry. The 236U/238U atom ratio was in the range 1.83-8.20 × 10-9 for fresh water and around 0.57 × 10-9 for seawater while the concentration of 236U was about 104-105 and 106 atoms/kg, respectively. Plutonium (239,240Pu) was detected in one riverine sample and the marine samples at very low levels and with large uncertainty. The concentrations of 137Cs in fresh riverine samples were 0.02-0..46 Bq/kg which are more than three orders of magnitude larger than the global fallout level. As for seawater samples within 80 km offshore of the FDNPP, the concentrations of 137Cs were 10-20 times higher than that of the Japan Sea water. Also 134Cs and 137Cs were of similar concentrations in all samples. The results show that volatile and refractory nuclides such as Cs, U and Pu exist in the dissolved phase, which can be readily assimilated by plants/humans. However the environmental impact of Pu and U in the vicinity of the FDNPP is considered to be low in comparison to that of the volatile radionuclide Cs.
Key words: uranium, plutonium, caesium, seawater, riverine water, Fukushima


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