Development of Advanced Environmental Transfer and Dose Assessment Modelfor Radionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Shun’ichi HISAMATSU, Takashi IYOGI, Shinji UEDA, Koichi ABE
Department of Radioecology
Abstract
We have developed an environmental transfer and dose assessment model (ETDAM) for radionuclides
released from the first commercial nuclear fuel reprocessing plant in Japan, located in Rokkasho. The
computer code system was developed on a PC to describe atmospheric dispersion, terrestrial and aquatictransfers, and dose calculations for the released radionuclides. We have used it to estimate areal and temporal
distributions of the radionuclides around the plant and the radiation doses resulting from them. The aquatictransfer model targeted transfer of radionuclides in Lake Obuchi, a brackish lake neighboring thereprocessing plant. The Lake Obuchi model consists of a water current model and an ecosystem model
including lower trophic level organisms. The advanced environmental transfer and dose assessment model(AdvETDAM) is now being developed. AdvETDAM will have the features of ETDAM, and furthermore
include a weather model, a catchment area model and an ecosystem model of higher trophic level organisms
for Lake Obuchi, and a coastal marine model. Development of AdvETDAM will be completed at the end ofFY 2010.
In FY 2008, we introduced the weather model to estimate metrological element data for more accurate
calculations of dispersion and deposition of atmospheric particles. The MM5 (Mesoscale Modeling System5th Generation) was introduced, and tested by using weather data at the reprocessing plant for one month ineach of the four seasons in 2007. While the wind direction and speed estimated agreed well with themeasured data (r=0.58 - 0.83), the difference between estimated precipitation rates and actual ones was large(r=0.36 - 0.66).
The catchment area model is being constructed to describe the inflow of radionuclides from Futamata
River, which is the main river flowing into Lake Obuchi. In FY 2008, the hydrological parameters wereoptimized to represent water inflow data of the river. A sub-model for transfer of chemical substances such as
N, P and C was also developed. A sub-model of a sea-grass colony in Obuchi Lake and marshland around thelake was developed as a part of the ecosystem model of higher trophic level organisms in the lake. While themodel of the sea-grass colony well describes biomass and basic production rate, the marshland model needs
to be improved for biomass representation. We also designed a 3D-hydrodynamic model as a base for thecoastal marine model to predict behavior of radionuclides released from the reprocessing plant through its
marine discharge pipe.

Wind direction
Wind direction at main stack exit
TemperatureWind speed
Wind speed at main stack exit
Precipitation

Correlation coefficient

1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30JanAprJulOct

Fig. 1 Correlation coefficient between estimated and meteorological elements measured at theRokkasho nuclear fuel reprocessing plant in for one month in each season in 2007.
Meteorological elements are at ground level except for wind speed which is at the mainstack exit.

Third calculation area
150 m gridSecond calculation area

JNFL release point

450 m gridFirst calculation area
1350 m grid

Third calculation area
150 m gridFig. 2Calculation area of coastal marine model for Rokkasho.