Validation of the Advanced Environmental Transfer and Dose Assessment Model forRadionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Takashi IYOGI, Koichi ABE, Naofumi AKATA, Hideki KAKIUCHI, Akira TAKEDA,Hidenao HASEGAWA, Shinji UEDA, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
The first commercial nuclear fuel reprocessing plant in Japan, located in Rokkasho, Aomori Prefecture
is now undergoing its final testing using actual spent nuclear fuels. The advanced environmental transfer anddose assessment model (AdvETDAM) was developed for estimating areal and temporal distributions of theradionuclides around the plant and the radiation doses resulting from these radionuclides. To validate themodel using actual field data, we measured the concentrations of radionuclides (3H, 14C, and 129I, etc.) invarious environmental samples collected at various points around the plant and the environmental -ray doseat 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 2012 were similar
to the background ones before the plant test operation, excluding several samples of soil and sediment.
Now, we have studied the distribution and transfer of several radionuclides in Fukushima Prefecture toclarify their movement in the terrestrial environment. The obtained results will be used to improve theaccuracy of the model prediction in AdvETDAM. We studied: 1) the re-suspension rate of radiocesium inKoriyama City and Namie Town; 2) the radiocesium interception potential (RIP) of farmland soil in
Fukushima Prefecture; 3) the transfer rate of radiocesium via two small rivers (the Hiso River and WarikiRiver) in a mountainous area in Iitate Village, Fukushima Prefecture; and 4) the distribution of 3H in plantand soil samples collected around the Fukushima Dai-ichi Nuclear Power Station (FDNPS).
The re-suspension rate of radiocesium ranged from 10-9 to 10-11, which was comparable to othervalues reported in the literature. Soil-to-plant transfer factor for soybean samples observed in 2011 wasnegatively correlated with the RIP value in soil. RIP and exchangeable K content in soil were useful indexes
for predicting the transfer factor. The discharge rate of radiocesium from the river catchments during 2012
was less than during 2011. We considered that the most of the radiocesium deposited in the catchments hasremained on the soil surface.
We collected various plant samples around the FDNPS in March, April, July and August 2011, andmeasured their free-water tritium (FWT) concentrations. Considerably higher FWT concentrations than thebackground 3H concentration were observed, and that showed that HTO was released from the FDNPS in
the nuclear accident. The committed effective dose from HTO inhalation was roughly estimated by using theFWT concentration obtained. The HTO concentration in the air was estimated from the FWT concentrationin plants by using the relationship between the atmospheric HTO and plant FWT concentration through therelative humidity in air. Although the FWT concentration decreased from March to August, we assumed thatthe value in March continued until the end of July, and the August value continued until the end ofDecember. The HTO inhalation dose about 20 km from the FDNPS was estimated to be roughly 3μSv.

Fig. 1 Free-water tritium (FWT) concentrations in herbaceous plant shoots and evergreen tree leaves
collected around Fukushima Dai-ichi Nuclear Power Station (FDNPS).