Improvement of the Advanced Environmental Transfer and Dose Assessment Model forRadionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Koichi ABE, Takashi IYOGI, Hidenao HASEGAWA, Shinji UEDA, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
We have developed the advanced environmental transfer and dose assessment model (AdvETDAM)
radionuclides released from the first Japanese commercial nuclear fuel reprocessing plant located in Rokkasho.
The computer code system was developed on personal computers to describe atmospheric dispersion, terrestrial
and aquatic transfers, and dose calculations for the released radionuclides. The model consists of an atmosphericdispersion model with a meteorological model (MM5), a terrestrial transfer model, an aquatic transfer model for
Lake Obuchi, which is a brackish lake neighboring the reprocessing plant, and its catchment area, and a coastal
marine model for the Rokkasho coast.
In FY 2014, to develop an aquatic radionuclide transfer model for Lake Takahoko, which is anotherbrackish lake near the reprocessing plant, and its catchment area, hydrological models were constructed todescribe water movement in the target areas. The hydrological data, including the water currents, the flux ofsedimentation matter and the submarine groundwater discharge rates were collected from Lake Takahoko toconstruct the hydrological model. To construct the hydrological model for the Lake Takahoko catchment area,hydrological data of water levels and residence time of groundwater, were collected in that area.
The Coastal Sea Modeling System for Hydrodynamic Processes (COSMOS) was adopted to simulate water
currents in Lake Takahoko, and numerical results obtained by the model for water current and salinity werecompared to the observed data. Also, the Water and Energy Transfer Process (WEP) model was adopted tosimulate water transfer in the catchment area in Lake Takahoko, and numerical results for river water discharge
and water level of ground water were in a good agreement with field measurements. Radionuclide transfer
models will be added to the hydrological models in FY 2015.
In FY 2014, we modified the atmospheric dispersion model of radionuclides to improve accuracy ofsimulated radiation dose and atmospheric concentration of 85Kr released from the reprocessing plant. The
accuracy of the dose and concentration was considerably improved by modifying several equations including
stochastic equations for the Random Displacement Method and transform factors for the vertical axis. In addition,
we wrote an interface program for using the Rader AMeDAS precipitation data, which have been analyzed andpublished by the Japan Meteorological Agency, as input to the atmospheric dispersion model for better
prediction of the washout process of radionuclides.

Fig. 1Monthly averaged -ray dose rate from discharged 85Kr during the period from April 2006 to October 2008.

Table 1

Consistency between simulated and measured monthly averaged concentrations and depositions for 3H
and 129I evaluated by Mean Errors (ME) and Root Mean Square Errors (RMSE) during the period fromApril 2006 to February 2009.

3

H concentration(Bq m-3)
3

H deposition(Bq m-2 month-1)
129

I concentration(Bq m-3)

129

I deposition(Bq m-2 month-1)

FY 2014

FY 2013

Measuredaverage

ME (Bq m-3)

RMSE (Bq m-3)

ME (Bq m-3)

RMSE (Bq m-3)

2.3×

3.3×

6.7×

-1.2×

2.7×

9.7×

2.3×

4.8×

2.9×

2.1×

1.8×

4.0×

2.0×

4.1×

9.9×

9.8×

9.4×

4.7×

-7.6×

1.7×