Improvement of the Advanced Environmental Transfer and Dose Assessment Model forRadionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Takashi IYOGI, Shinji UEDA, Hidenao HASEGAWA, Koichi ABE, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
We have developed the advanced environmental transfer and dose assessment model (AdvETDAM 1.0) forradionuclides released from the first Japanese commercial nuclear fuel reprocessing plant 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. The model consists of an atmospheric dispersion
model with a meteorological model (MM5), a terrestrial transfer model, an aquatic transfer model in Lake
Obuchi , which is a brackish lake neighboring the reprocessing plant, and its catchment area and a coastal marine
model for the Rokkasho coast.
To improve accuracy of the AdvETDAM 1.0, during FYs 2011 – 2012 we are planning to develop
submodels that describe (1) dispersion of radioiodine in different physical forms in the atmosphere, (2) snow
accumulation and melting on the ground, and (3) weathering of the radionuclides from leaf surface of crop plants
by rainfall. Since 3H discharged from the reprocessing plant into the Pacific Ocean was detected in Lake
Takahoko, which is another brackish lake near the reprocessing plant, an aquatic transfer model in the lake andits catchment area will be developed during FYs 2013-2015. A sensitivity analysis routine of parameters will bealso installed into the AdvETDAM by FY 2015.
In FY 2011, the first submodel to describe atmospheric dispersion of radioiodine was developed, because
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I concentrations estimated by the AdvETDAM 1.0 did not agree well with measurement results. In thatsubmodel, gaseous radioiodine and particulate radioiodine in the atmosphere were separately treated, anddeposited at different velocities for each form. The AdvETDAM 1.1 was made by installing the submodel into
the AdvETDAM 1.0. We separately measured gaseous and particulate 129I concentrations in the atmosphere atIES, while the discharge rate from the main stack of the reprocessing plant was given as a total of gaseous andparticulate 129I. The proportion of gaseous 129I at the main stack was estimated by repeated calculation of theatmospheric dispersion to minimize the difference between the calculated and measured proportion. Although
the atmospheric 129I concentrations calculated with the estimated proportion had better agreement with themeasured ones than those obtained by the AdvETDAM 1.0, the agreement in the 129I deposition values wassomewhat deteriorated. Since the gaseous proportion of 129I in the atmosphere depends on climate conditions (airtemperature, humidity and solar radiation), a sub-program for estimate the proportion from the climate
conditions was installed.
In order to evaluate environmental transfer of 3H including snow accumulation and melting, the NoahLand-Surface model and the Soil and Water Assessment Tool were selected for examination. We will choose thebetter one from the comparative calculations with measured results and install it into the AdvETDAM 1.1.
We collected the basic hydrological data of Lake Takahoko and its catchment area for model construction,including the bathymetry and water quality (salinity etc.) of the lake, and geological setting, hydraulicconductivity of geological samples, groundwater level and river water flow rate in the catchment area.

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Factor 2

Factor 5

Agreement ratio (%)

50403020
100
AdvETDAM 1.0Observed value

Depending on
relativehumidity

Depending on
global solar
radiation

Depending on
temperature(1) Atmospheric concentration
60
Factor 2

Factor 5

Agreement ratio (%)

50403020
100
AdvETDAM 1.0 Observed value

Depending on Depending on
relative humidity global solar
radiation

Depending on
temperature(2) Deposition
Fig. 1 The calculation results of 129I using the ratio of
the gaseous form which changes depending on
climate conditions.
Calculation conditions with AdvETDAM:
calculation area, 50 x 50 km with a grid
resolution of 500 x 500 m; 2,400 m above
ground with 26 vertical intervals varying from 10m to 175 m; calculation period, from Apr. 2006
to Dec. 2008.