Investigations in Kawauchi Village, Fukushima Prefecture, have revealed that the amount of cesium outflow from small water systems (where a person can look out over whole area) is lower by one order of magnitude than that from an experimental plot located at the slope of a mountain forest.

Fig.1　Image of experimental plot

Table 1　Outflow amount and its rate radioactive cesium and soil at hte slope experimental plot in Ogi District, Kawauchi Village
(November 12, 2013-October 20, 2014)

A：Outflow amount of soil (1 year, 1 m2)	0.012 kg/m2
B：Concentration of radioactive cesium in outflowing soil (137Cs)	16 kBq/kg
C：Amount of outflowing radioactive cesium (1 year, A×B)	0.19 kBq/m2
D：Amount of cesium deposition in soil around experimental plot	770 kBq/m2
E：Rate of outflowing radioactive cesium (1 year, C/D)	0.03 ％

Table 2　Amount of soil and cesium outflow in a small water system in Ogi District, Kawauchi Village
(June 27-September 30, 2014)(three months)

A：Amount of outflowing soil (3 months, total river basin)	4.9 kg
B：Concentration of radioactive cesium in outflowing soil (137Cs)	about 64 kBq/kg
C：Amount of outflowing radioactive cesium per 54,000m2 (3 months, A×B)	about 314 kBq
D：Amount of outflowing radioactive cesium per 1m2 (3 months, C/54,000)	about 0.0058 kBq/m2
E：Amount of outflowing radioactive cesium per 1m (1 year, D×4)	0.023 kBq/m2

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Reference

1. 長尾ほか(2019), 福島における放射性セシウムの環境動態研究の現状（平成30年度版）, JAEA-Research 2019-002, 235p.