Validation of the Advanced Environmental Transfer and Dose Assessment Model forRadionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Shinya OCHIAI, Hidenao HASEGAWA, Hideki KAKIUCHI, Shinji UEDA,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 under safety assessment by the Nuclear
Regulation Authority. The advanced environmental transfer and dose assessment model (AdvETDAM) wasdeveloped for estimating areal and temporal distributions of the radionuclides around the plant and theradiation doses resulting from these radionuclides. To validate the model using actual field data, wemeasured the concentrations of radionuclides (3H, 14C, 129I, etc.) in various environmental 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,
concentration levels of the radionuclides in most environmental samples collected in FY 2014 were similar
to the background ones before the plant test operation, excluding several samples. Iodine-129 deposited on
soil and sediment surfaces has still remained at a higher level than each background level.
Since the accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in 2011, we have studied
the distribution and transfer of several radionuclides in Fukushima Prefecture to clarify their movement in
the terrestrial environment. The obtained results will be used to improve the accuracy of the model
prediction in AdvETDAM. In FY 2014, we studied the following subjects: 1) the re-suspension rate ofradiocesium in Koriyama City and Namie Town; 2) the distribution of 3H in plant and soil samples collectedaround the FDNPP; 3) the discharge rate of radiocesium via two small rivers in a mountainous area in Iitate
Village; and 4) the distributions of dissolved and particulate 137Cs concentrations under base-flow conditions
in seven river systems in Fukushima Prefecture.
The atmospheric 137Cs concentrations were found to depend on the frequency of wind direction from ahigher contaminated area and the re-suspension rate of 137Cs has been gradually decreasing with time.
Higher free-water tritium (FWT) and organically bound tritium (OBT) concentrations than the background3
H concentration were observed, reflecting HTO released from the FDNPP accident. These concentrations
have been gradually decreasing from 2011 to 2014. The discharge rate of radiocesium from the rivercatchments of the two small rivers during 2014 was less than that during 2011 and similar to that during
2012, showing that most of the radiocesium deposited in the catchments has still remained on the soil
surface. The concentration of dissolved 137Cs in water samples form the seven rivers in each year was
significantly correlated with the mean 137Cs inventory in the catchment area above each sampling point
during 2012–2014. Those results suggest that the dissolved 137Cs under base-flow conditions originates fromthe whole area of the catchment, and its concentration is primarily determined by the mean 137Cs inventoryof the catchment area. On the other hand, the concentration of particulate 137Cs in river water did not show aclear relationship with the mean 137Cs inventory, indicating that the concentration does not simply reflect theinventory of the whole catchment area.

ManoNiida
Ohta
Odaka
Ukedo

Dissolved 137Cs concentrationin river water (Bq L-1)
(Bq g-1-SS_dry)

Uta

137Cs concentration in SSAbukuma
RiverFDNPP

Mean 137Cs inventory (MBq m-1)

Fig. 1 Sampling points of river water. Map data were based

Fig. 2 Relationships between the mean 137Cs

on National Land Numerical Information (Ministry ofinventory in the catchment and theLand, Infrastructure, Transport and Tourism).

dissolved 137Cs concentration in riverwater, and 137Cs concentration in SS.