Distribution of local 137Cs anomalies on the seafloor near the Fukushima Dai-ichi Nuclear Power Plant

An estimated 3.5 +/- 0.7 x 1015 Bq of Cs-137 is thought to have been discharged into the ocean following the melt down at Fukushima Dai-ichi Nuclear Power Plant (F1NPP). While efforts have been made to monitor seafloor radiation levels, the sampling techniques used cannot capture the continuous distribution of radionuclides. In this work, we apply in situ measurement techniques using a towed gamma ray spectrometer to map the continuous distribution of Cs-137 on the seafloor within 20 km of the F1NPP. The results reveal the existence of local Cs-137 anomalies, with levels of Cs-137 an order of magnitude higher than the surrounding seafloors. The sizes of the anomalies mapped in this work range from a few meters to a few hundreds of meters in length, and it is demonstrated that the distribution of these anomalies is strongly influenced by meter scale features of the terrain.(C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.