Validation of the Advanced Environmental Transfer and Dose Assessment Model forRadionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Hidenao HASEGAWA, Hideki KAKIUCHI, Yuhi SATOH, Shinji UEDA
Yuichi TAKAKU, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
The final testing using actual spent nuclear fuels is mostly finished for the first commercial nuclear
fuel reprocessing plant in Japan, located in Rokkasho, Aomori Prefecture and the plant is now under safetyassessment by the Nuclear Regulation Authority. The advanced environmental transfer and dose assessment
model (AdvETDAM) was developed for estimating areal and temporal distributions of the radionuclides
around the plant and the radiation doses resulting from these radionuclides. To validate the model using
actual field data, we measured the concentrations of radionuclides ( 3H, 14C, 129I, etc.) in environmental,
agricultural, and livestock samples collected at points around the plant and we also measured theenvironmental -ray dose rates at IES.
Because no nuclear fuel rods have been sheared or dissolved at the plant since October 2008, wefound concentration levels of the radionuclides in most environmental samples collected in FY 2017 weresimilar to the background ones before the plant test operation, excluding several samples. Iodine-129
deposited on soil and lake sediment surfaces around the plant has still remained at a higher level than theirrespective background levels. We also found that the concentrations of radionuclides (3H, 14C and 129I) in
agricultural products, which were produced in an experimental agricultural field at IES for the study ofradionuclide transfer from the atmosphere to these products, were similar to their background levels.
To improve the accuracy of the model prediction in AdvETDAM, we have been investigating thedistributions and transfer of radionuclides in the terrestrial environment in Fukushima Prefecture after theaccident at the Fukushima Dai-ichi Nuclear Power Plant. In FY 2017, we continued to study the following
subjects: 1) the re-suspension rate of 137Cs and 2) the discharge rate of 137Cs via rivers. The atmosphericconcentrations and deposition fluxes of 137Cs gradually decreased during FY2012 to 2015 with different
effective half-lives, however, both half-life values after 2015 have become nearly constant. Clear seasonality
was found with a high atmospheric 137Cs concentration in summer and a low concentration in winter which
was the same as our previous observation. The wind direction weighted mean re-suspension factor of 137Cs
in Namie, Fukushima Prefecture (1.0×10-11 - 1.0×10-9 in FY 2013 - 2017) has become similar to or lower
than the annual mean re-suspension factor (atmospheric 137Cs concentration)/(137Cs deposition density),observed at Chernobyl and in European countries (1×10-10 - 1×10-6). Concentrations of dissolved 137Cs inwater samples from seven small rivers in Fukushima Prefecture correlated well with the 137Cs inventories intheir catchments, with annually decreasing values for the (dissolved 137Cs concentration)/(137Cs inventory)
ratio during FY2012-2017.

137Cs deposition flux (Bq m-2 d-1)
Atmospheric 137Cs concentration (mBq m-3)

1E+2

1E+1

1E+0

Atmosphericconcentration

Effective half-life: 0.6 yy = 83.8 exp(-1.12 x)

DepositionfluxDeposition flux

Atmosphericconcentration

1E-1y = 9.2×10-1 exp(-0.53 x)
Effective half-life: 1.3 y
1E-201234
Time since the accident (y)567Fig. 1 Temporal variation of averaged monthly atmospheric concentration and deposition flux of 137Cs
observed in Namie, Fukushima Prefecture.

1E-8

Wind direction weighted
re-suspension factor (m-1)

re-suspension factor
Effective half-life: 1.2 y
1E-9y = 8.48×10-10 exp(-0.56x)

1E-10

1E-11

1E-1201234
Time since the accident (y)567Fig. 2 Temporal variation of the wind direction weighted mean re-suspension factor of 137Cs in Namie,
Fukushima Prefecture.