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, Shinji UEDA
Yuichi TAKAKU, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
The first commercial nuclear fuel reprocessing plant in Japan, located in Rokkasho, Aomori Prefecturefinished its final testing using actual spent nuclear fuels and is now undergoing safety assessment by theNuclear Regulation Authority. The advanced environmental transfer and dose assessment model(AdvETDAM) was developed for estimating areal and temporal distributions of the radionuclides around theplant and the radiation doses resulting from these radionuclides. To validate the model using actual field
data, we measured the concentrations of radionuclides (3H, 14C, 129I, etc.) in environmental, agricultural, andlivestock samples collected at points around the plant and 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 2018 weresimilar to the background ones before the plant test operation, excluding 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 excess 129I inventory in surface soil collected around the reprocessing plant has beenobtained by subtracting the global fallout-derived 129I inventory from the total 129I inventory of soil, and it
has been compared with estimated 129I deposition density using AdvETDAM. The geographical distribution
pattern of estimated 129I deposition density agreed relatively well with measured excess 129I inventory in soil,except the north area of the reprocessing plant site which AdvETDAM evaluated to be the maximum 129I
deposition area.
To improve the accuracy of the model prediction in AdvETDAM, we investigated the distributions
and transfer of radionuclides in a terrestrial environment in Fukushima Prefecture after the accident at theFukushima Dai-ichi Nuclear Power Plant. In FY 2018, we continuously studied the following subjects: 1)
the re-suspension rate of radiocesium and 2) the discharge rate of radiocesium via rivers. The atmosphericconcentrations 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 highatmospheric 137Cs concentration in summer and low concentration in winter was found the same as in ourprevious observations. We measured concentrations of 137Cs and 129I in suspended load samples collected in
two small rivers in Iitate during 2018 and found that both concentrations correlated with those of organicmaterials in the samples.

0.05
0.11

0.21

0.05

0.03

0.13

N0.05

0.08

Excess 129I inventory(Bq m-2)

0.01

0.06

: FY2018: FY2006-FY2017

0.21 0.09

0.15
0.20

0.17

0.04

0.03
0.08

主排気筒
0.24 Main
stack

0.04
0.10

0.09

Estimated 129I
deposition(Bq m-2)

環境研
IES

0.06
0.07

0.07

0.03

1.00 - 5.00
0.50 - 1.00
0.10 - 0.50
0.05 - 0.10
0.01 - 0.05
0.00 - 0.01

0.10

0.04

02 km

0.01
Fig. 1 Distribution map of measured excess 129I inventory in surface soil and estimated 129I deposition obtainedusing AdvETDAM.