Validation of the Advanced Environmental Transfer and Dose Assessment Model forRadionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Takashi IYOGI, Koichi ABE, Naofumi AKATA, Hideki KAKIUCHI
Hidenao HASEGAWA, Shinji UEDA, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
The first commercial nuclear fuel reprocessing plant in Japan, located in Rokkasho, Aomori
Prefecture is now undergoing its final testing using actual spent nuclear fuels. 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 the radionuclides.
To validate the model using actual field data, concentrations of radionuclides (3H, 14C, and 129I, etc.) invarious environmental samples collected around the plant and the environmental γ-ray dose at IES weremeasured. Because no nuclear fuel rods have been sheared or dissolved at the plant since October 2008,
concentration levels of the radionuclides in most environmental samples collected in FY 2011 were similar
to the background ones before the plant test operation, excluding several samples of soil and sediment.
The validation results of AdvETDAM, that is monthly γ-ray dose rates from 85Kr at IES, are reported
here using the data obtained from April 2006 to February 2009 (FYs 2006-2008) when many nuclear fuelrods were sheared and dissolved and significant amounts of radionuclides were released from the plant. A
four-dimensional data assimilation technique was applied to wind velocity and direction for improving
accuracy of estimated γ-ray dose rate by 85Kr. Although the accuracies of the predictive values for windvelocity and direction were improved, that for the γ-ray dose rate was not. Further study is required toimprove the accuracy of the model.
Distribution and transfer of several radionuclides in Fukushima Prefecture were studied to clarify theirmovement in the terrestrial environment. The obtained results will be used for AdvETDAM to improve theaccuracy of model prediction. We researched the re-suspension rate of radiocesium in Koriyama City,
distribution of 3H (FWT, OBT) in plant and soil samples around Fukushima Dai-ichi Nuclear Power Plantand transfer rate of radiocesium via two small rivers (the Hiso River and Wariki River) in a mountainous
area in Iitate Village, Fukushima Prefecture. Results of the transfer rate of radiocesium via the rivers aremainly reported here. The discharge rates of radiocesium in 2011 via the Hiso and Wariki Rivers were
estimated as 0.5% and 0.3% of the total inventory of the catchment area of each river, respectively, by theanalysis of measurement results of river water flow rate and transfer rate of radiocesium and precipitation
data from the literature. Most of the radiocesium was transported as a particulate form in river water.

NWariki River

Niida River

Hiso RiverFukushima
Prefecture

PacificOcean

30 km line

Fukushima
Daiichi Nuclear
Power Plant

Fig. 1 Sampling locations.

Fig. 2 Concentration of radiocesium inriver water samples.
Measuredat several times

Estimate（290 days）

Precipitation

Calculation
Regression
formulaWater level

Regression
formulaWaterdischarge

Water level

Water
discharge

Concentrationof radiocesium

Fig. 3 Relationships between the discharge ofradiocesium and the water discharge rateof the river waters.

Regression
formulaDischarge ofradiocesium

Fig. 4 Scheme to estimate radiocesium
discharge from rivers.