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, Hidenao HASEGAWA, Shinya OCHIAI,Hideki KAKIUCHI, Akira TAKEDA, 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, 129I, etc.) in various
environmental samples collected at various points around the plant and the environmental -ray dose rates atIES.
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 2013 were similarto 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 Station (FDNPS) in 2011, we havestudied 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 themodel prediction in AdvETDAM. In FY 2013, we studied the following subjects: 1) the re-suspension rateof radiocesium in Koriyama City and Namie Town, 2) the distribution of 3H in plant and soil samples
collected around the FDNPS, 3) the radiocesium interception potential (RIP) of farmland soil around
Fukushima Prefecture, and 4) the discharge rate of radiocesium via two small rivers (the Hiso River andWariki River) in a mountainous area in Iitate Village, Fukushima Prefecture.
The re-suspension rate of radiocesium ranged from 10-10 to 10-8, which was comparable to othervalues reported in the literature. Higher free-water tritium (FWT) and organically bound tritium (OBT)
concentrations than the background 3H concentration were observed showing HTO release from the FDNPS
accident. These concentrations have been gradually decreasing from 2011 to 2013. Soil-to-plant transfer
factor for soybean samples collected from contaminated fields in 2012 was found to be negatively correlatedwith the radiocesium interception potential (RIP) value and exchangeable K content in soil. This showedthat 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 2013 was less than that during 2011 andsimilar to that during 2012, showing that the most of the radiocesium deposited in the catchments has still
remained on the soil surface.

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Excess 129 I (Bq m -2 )5 E-2

Rokkasho Village
Fig. 1 Estimated 129I inventories originating from the nuclear fuel reprocessing plant on the south side of brackish
Lake Obuchi, Rokkasho, Japan. ○: Sampling point ●: Main stack of the nuclear fuel reprocessing plant

129I inventory (Bq m‐2)

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Fig. 2 Variation of the 129I inventories in sediments from the western and central areas in brackish Lake Obuchi,Rokkasho, Japan.