11:45 AM - 12:00 PM
[MAG38-11] Transport of radiocesium in the Niida River, Fukuhsima Prefecture in 2011-2014
Keywords:Cs-134, Cs-137, rain event, riverine suspended solids
Field experiments were conducted at a fixed station (Kinouchi bridge) in the lower Niida River during the period of May 2011-December 2014. The 20 L of surface river water samples were collected at the station using buckets. The radioactivity of 134Cs and 137Cs in the river waters before and after the filtration was measured with gamma-ray spectrometry using ammonium molybdophosphate (AMP)/Cs compound method.
Total radioactivity of 137Cs (dissolved and particulate phases) in the river waters ranged from 0.11 to 4.18 Bq/L during May 2011-December 2014. Highest value was found in May 2011. Total 137Cs radioactivity indicates the decreasing trend with increasing time at normal flow condition. However the higher radioactivity was observed after rain events. The 137Cs radioactivity increased by 1.83 Bq/L after the heavy rain event by Typhoon Guchol in June 2012, and 1.68 Bq/L by Typhoon Jelawat in October 2012.
Percentage of 137Cs associated with riverine suspended solids was 47-48% at normal flow condition in July and September 2011, but after December 2011 ranged from 75 to 93% at normal flow condition and 86-91% at high flow condition due to rain events. The radioactivity of particulate phase of 137Cs ranged from 20 to 42 Bq/g-riverine suspended solids. Rain events are mainly contributed to the transport of radiocesium in the Niida River.