~(236)U and radiocesium in river bank soil and river sediment in Fukushima Prefecture, after the Fukushima Daiichi Nuclear Power Plant accident

摘要

Almost 8 years after the Japanese Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, data for U-236 and U-236/U-238 have mainly remained limited to only a few heavily contaminated samples. In the present study, activities of U-236, (CS)-C-134, and Cs-137, along with U-234, U-235, U-238 in 15 river bank soil and 10 river sediment samples, were measured by ICP-MS/MS and gamma spectrometry. The Cs-134 activities and Cs-134/Cs-137 activity ratios (decay-corrected to March 11, 2011) in these 15 river bank soil samples were from 74.8 to 3.88 x 10(5) Bq kg(-1) and from 0.944 to 1.02, respectively; and in these 10 river sediment samples were from 87.1 to 1.86 x 10(5) Bq kg(-1) and from 0.904 to 0.990, respectively. The U-236 activities and U-236/U-238 atom ratios in these soil samples were in the respective ranges of (0.139-17.6) x 10(-5) Bq kg(-1) and (0.259-3.83) x 10(-8); and in these sediment samples were in the respective ranges of (0.884-27.0) x 10(-5) Bq kg(-1) and (1.12-5.04) x 10(-8). For one river sediment core sample, Cs-134 and U-236 activities decreased with the depth indicating Cs-134 and U-236 accumulated in the river sediment with time. Unlike Cs-134, no clear evidence of FDNPP accident-derived U-236 has been found in this study, although further monitoring is encouraged to establish the background database on U-236/U-238 for its potential application as a tracer in environmental studies. (C) 2019 Elsevier Ltd. All rights reserved.