Improvement of the Advanced Environmental Transfer and Dose Assessment Model forRadionuclides Released from the Nuclear Fuel Reprocessing Plant in Rokkasho
Koichi ABE, Kazuhiro OSHIMA, Shinji UEDA, Yuichi TAKAKU, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
We have developed the advanced environmental transfer and dose assessment model (AdvETDAM) forradionuclides released from the first Japanese commercial nuclear fuel reprocessing plant located in Rokkasho.
To describe the radionuclides transfer in each target sphere, the AdvETDAM consists of: an atmosphericdispersion model with a mesoscale meteorological model (MM5), a terrestrial transfer model, aquatic transfer
models for Lakes Obuchi and Takahoko, which are brackish lakes neighboring the reprocessing plant, and theircatchment areas, and a coastal marine model for the Rokkasho coast.
To improve accuracy of simulation by the atmospheric dispersion model, four data assimilation procedures,
which were designed in FY 2016 and introduced in FY 2017, were evaluated in FY 2018. The assimilation
procedures were applied to wind field calculations in the mesoscale meteorological model and the dispersionmodel. In addition, we tried to improve the Lagrangian particle dispersion calculation by three approaches: 1)
modifying averaged atmospheric 3H discharge rates from the main stack for every ~1 week to discharge rates
different in each day to represent well the atmospheric 3H concentrations measured around the main stack, 2)
modifying plume raise height using 85Kr concentrations measured around the main stack and 3) estimating
mixing height based on data measured by a ceilometer at our institute. The evaluation results showed that thedata assimilation in the wind field calculations and approach 1) were effective, giving simulation results
closer to the measured ones with the assimilations. Although approaches 2) and 3) were not effective for
estimating 85Kr concentrations, approach 3) was considered to provide reasonable mixing heights based on themeasured data.
To assess uncertainties of results by the AdvETDAM, the probabilistic assessment function for exposed
dose was designed in FY 2018, and it will be introduced in FY 2019. The uncertainty analysis of simulation
results for accidental discharges was designed by referring to the level 3 probabilistic risk assessment for anuclear power plant, while that for discharge under normal operation was also roughly designed.
For realistic simulation of 14C and 3H transfers from the atmosphere to agricultural products in theterrestrial transfer model, the dynamic transfer models developed in our previous studies were introduced for the14C transfer, while the 3H transfer in the same routes was designed in FY 2018. In addition, to simulate

radionuclide transfers in the Lake Obuchi model and Rokkasho coastal model over a year, a restart function wasinstalled in those models.

(a) November 2007
Fig. 22.0
1.0

***

** **
Station 9* * * *0.0

Station 8

Station 9Station 8

Station 7

Station 6*
Station 5*
Station 4

Station 2

0.0

Station 3

* * *

3.0

Station 7

1.0(* value below 0.1)

Station 6

2.0

4.0

Station 5

3.0

Measurement
Simulation (without assimulation)
Simulation (with assimulation)

Station 4(* value below 0.1)

5.0

Station 3

4.0

6.0

Station 2

5.0

Measurement
Simulation (without assimulation)
Simulation (with assimulation)

Station 1

6.0

Mean concentration (mBq m -3)

Location of measurement stations. There are 9 measurement stations including No. 1 located at IES and No. 2
located at AMBIC. The star marks location of the plant main stack.

Station 1

Mean concentration (mBq m -3)

Fig. 1(b) September 2008

Masurement and simulation values of atmospheric 3H concentrations during the final test operation of thenuclear fuel reprocessing plant using actual spent fuel in November 2007 and September 2008. Blue, black andred bars denote mesurement value, and simulation values with assimulation and without assimulation,
respectively.