- JAEA has carried out “the project on the Long-term Assessment of Transport of Radioactive Contaminant in the Environment of Fukushima (F-TRACE project)” since the end of 2012. Radioactive caesium has been distributed by the fall out by Fukushima Dai-ichi Nuclear Power Plant (1F-NPP) accident, and forests in mountain areas have large amount of inventory of radioactive caesium and cover relatively large part of contaminated area of Fukushima. In this project, the transport behavior of radioactive caesium from the forests to biosphere and sea is evaluated by computer simulation based on the results of field observation and laboratory experiments. The results are used to predict evolution of effective dose of the residents in the affected area due to the transport, specify the dominant pass way of caesium, and propose effective methodology to constrain the transport along the pass way.
- The field investigations were conducted focusing on the river transport including forest, rivers, dams, reservoirs, and estuary. The data displayed here were based on the river survey results of air dose rates on the river sides.
- Six rivers at Hamadori area including Ukedo river (with Takase river), Ota river, Odaka river, Maeda river, Kuma river, and Tomioka river (with Oginosawa river) were surveyed. Ten to twenty measurement points were selected in each river from the upstream to the estuary. Along the river cross-section, each measurement point included a multiple number of sampling points.
- Measurements were conducted from December 2012 to March 2013, September 2013, November 2013, October 2014 to December 2014, September 2015 to November 2015, November 2016, and December 2016.
- Using a NaI(Tl) scintillation survey meter for the measurement, air dose rates (ambient dose equivalent rates) at the height of 1 m above the ground were measured.
- The measurement data includes air dose rates for natural radionuclides.
