Development of the Advanced Environmental Transfer and Dose Assessment Model forRadionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Shun’ichi HISAMATSU, Takashi IYOGI, Shinji UEDA, Hidenao HASEGAWA, Koichi ABE
Department of Radioecology
Abstract
We have developed an environmental transfer and dose assessment model (ETDAM) for radionuclides
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. We have used the ETDAM to estimate areal
and temporal distributions of the radionuclides around the plant and the radiation doses resulting from theradionuclides. The aquatic transfer model targeted transfer of radionuclides in Lake Obuchi, a brackish lakeneighboring the reprocessing plant. The Lake Obuchi model consists of a water current model and anecosystem model including lower trophic level organisms.
To increase accuracy and target areas of ETDAM, a meteorological model (MM5) for the atmosphericdispersion model, a catchment area model for Lake Obuchi, an ecosystem model of higher trophic level
organisms for the lake, and a coastal marine model have been developed during FYs 2006 - 2010. Thosemodels were bound to ETDAM, and integrated as the advanced environmental transfer and dose assessment
model 1.0 (AdvETDAM 1.0) in FY 2010. Meteorological elements such as wind direction and velocity
calculated by the meteorological model are introduced into the atmospheric dispersion model. The catchment
area model describes the inflow of radionuclides from the Futamata River, which is the main river flowing
into the lake. A sub-model including ellgrass (Zostera marina), fishes and benthos was developed as theecosystem model of higher trophic level organisms in the lake. The coastal marine model for Rokkasho
Coast simulates inflow of radionuclides from the Pacific Ocean into the lake through Obuchi Fishing Port at
the mouth of the lake to the ocean.
The 3H concentrations in lake water samples collected from Lake Obuchi in November 2007, whichwere higher than the background level, were simulated by using AdvETDAM 1.0 to confirm its function.
The possible sources of 3H in the lake water were surface deposition of atmospheric released 3H, and inputs
from the Futamata River and the Pacific Ocean. Estimated 3H concentrations of surface lake water at thecenter of the lake agreed fairly well with the measured values; estimated values were 1.7 - 2.8 times lower
than the measured values. The source of 3H in the lake was considered as the liquid waste release from theplant to the ocean because of an underestimated factor of 9 - 10 without input from the ocean. The
contributions of the atmospheric deposition and input from Futamata River were minor in comparison withthe input from the ocean. Although AdvEDAM 1.0 simulated fairly well the 3H concentrations in the lakewater, the estimated concentrations were systematically lower than the observed ones. The input from theFutamata River was also overestimated with the model. Further study is required for improvement ofsimulation with AdvETDAM 1.0.

Discharge tothe atmosphere

Concentration
in atmosphere

The atmosphericdiffusion model

The terrestrial
transfer model

Atmosphericdeposition

The meteorologicalmodel ①

External dose

Concentration inagricultural productsInternal dose

Concentrationin lake water

The ecosystemmodel of lower
trophic levelorganisms in
Lake Obuch ②

Concentration inlivestock products

The ecosystemmodel of higher
trophic level
organisms in
Lake Obuch ③

Concentrationin plankton

Concentration inlake sediments
Concentration ineelgrass
Concentration infish and shellfish

Discharge
to the sea

The catchment areamodel of Lake Obuch ④

Concentration inriver water

The coastal marine modelof Rokkaysho ⑤

Concentration in
sea water

Concentration infish and shellfish： The terrestrial transfer and dose assessment model ⑥： The environmental transfer and dose assessment model ⑦

Fig.1

Scheme of the AdvETDAM 1.0 for transfer and dose assessment forradionuclides discharged from the nuclear fuel reprocessing plant in Rokkasho

Mouth of Futamata River (MFR)

Obuchi Fishing Port (OFP)

Center of Lake Obuchi(CLO)

Measured

Estimated

Estimated (without input from the ocean)● At CLO

At CLO------ At CLO◆ At OFPAt OFP------ At OFP▲ At MFR

At MFR-1

H concentration (Bq L )

100

101

3

0.1

0.01
1-Sep-2007

Fig.2

1-Oct-2007

1-Nov-2007

1-Dec-2007

1-Jan-2008

Concentrations of 3H in surface water samples at the center of Lake Obuchi (CLO), ObuchiFishing Port (OFP) and the mouth of Futamata River (MFR) estimated with AdvETDAM 1.0.
The dashed line (in red and green) shows the simulation without input of 3H from the ocean.