Validation of the Advanced Environmental Transfer and Dose Assessment Model forRadionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Hidenao HASEGAWA, Hideki KAKIUCHI, Yuhi SATOH, Akinobu ISHIMINE
Shinji UEDA, Yuichi TAKAKU
Department of Radioecology
Abstract
The first commercial nuclear fuel reprocessing plant in Japan, located in Rokkasho, Aomori
Prefecture finished its final testing using actual spent nuclear fuels and it is now preparing for full operation.
The advanced environmental transfer and dose assessment model (AdvETDAM) was developed toestimate areal and temporal distributions of radionuclides around the plant and the radiation doses resulting
from these radionuclides. To validate the model using actual field data, we measured the concentrationsof radionuclides (3H, 14C, 129I, etc.) in environmental, agricultural and livestock samples collected at points
around the plant, and we also measured the environmental -ray dose rates at IES.
Because no nuclear fuel rods have been sheared or dissolved at the plant since October 2008, wefound concentration levels of the radionuclides in most environmental samples collected in FY 2020 weresimilar to the background ones before the plant test operation, except for several samples. Iodine-129
deposited on soil and lake sediment surfaces around the plant has still remained at a higher level than eachbackground level. The mean 129I deposition fluxes observed at the IES site, Futamata and Hirosaki fromFYs 2016 to 2020 were approximately the same level: 2.0±2.9E-6, 1.9±3.3 E-6 and 2.1±3.9E-6 Bq m-2 d1, respectively. In addition, the temporal variations of 129I deposition fluxes at the IES site, Futamata andHirosaki have shown similar patterns: high in winter and low in other seasons. These observed facts canbe reasonably explained by assuming that the 129I discharged from commercial reprocessing plants inEurope was transported long distances by winter monsoons.
To improve the accuracy of the model prediction in AdvETDAM, we have investigated thedistributions and transfer of radionuclides in a terrestrial environment in Fukushima Prefecture after theaccident at the Fukushima Dai-ichi Nuclear Power Plant. In FY 2020, we continuously studied twosubjects: the re-suspension rate of radiocesium; and the discharge rate of radiocesium via rivers. Theatmospheric concentrations and fluxes of 137Cs gradually decreased during FYs 2012 to 2015 with different
effective half-lives, however, both values after 2015 have become nearly constant. The clear seasonality
with high atmospheric 137Cs concentration in summer and low concentration in winter that we reported in
our previous studies was not found. The estimated discharge rate of 137Cs from the river catchments of thetwo small rivers in Iitate Village since 2011 was less than 2% of 137Cs deposited in the catchments, showingthat most of the 137Cs has still remained on the soil surface in the catchments.

1E-4

Hirosaki

RokkashoHirosaki

NFutamataMain exhaust stackIES

129I deposition flux (Bq m-2 d-1)

1E-5
1E-6
1E-7
1E-4

Futamata (west)

1E-5
1E-6
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IES (east)

1E-5
1E-6
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2016
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2 KmFig. 1

2017
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2018
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2019
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Temporal variations of 129I deposition flux at the IES site, Futamata and Hirosaki.

2020
R2