Brief introduction to research on geological disposal of high-level radioactive waste

Yamaguchi, Masaaki

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(1), p.38 - 41, 2022/06

https://nuce.aesj.or.jp/jnuce/vol29/jnuce-vol29-1-p38-41.pdf

This presentation outlined the framework and background of Japan's geological disposal research that has been underway since the 1970s and outlined research and development on the engineering technology of geological disposal and the performance assessment of geological disposal systems in the research and development fields. Specific assessment methods used in both R & D fields and recent research topics were also explained.

Analytical tool of evolution of topography and repository depth to assess impacts of uplift and erosion for HLW disposal

Yamaguchi, Masaaki; Kato, Tomoko; Suzuki, Yuji*; Makino, Hitoshi

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(2), p.72 - 82, 2020/12

https://doi.org/10.3327/jnuce.27.2_72

An efficient analytical tool to calculate temporal change of topography and repository depth due to uplift and erosion was developed for use in performance assessment of high level radioactive waste geological disposal. The tool was developed as ArcGIS model, incorporating simplified landform development simulation, to enable trial calculation of various conditions such as initial topography, uplift rate and its distributions, and repository location. This tool enables to support decision on which processes, features, and their changes should be taken into account for performance assessment, by calculating topography change and repository depth change under various conditions.

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018)

Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.

JAEA-Research 2019-002, 235 Pages, 2019/08

JAEA-Research-2019-002.pdf:21.04MB

The accident of the Fukushima Daiichi Nuclear Power Station (hereinafter referred to 1F), Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, JAEA has been conducting Long-term Environmental Dynamics Research concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.

Ion hydration and association in an aqueous calcium chloride solution in the GPa range

Yamaguchi, Toshio*; Nishino, Masaaki*; Yoshida, Koji*; Takumi, Masaharu*; Nagata, Kiyofumi*; Hattori, Takanori

European Journal of Inorganic Chemistry, 2019(8), p.1170 - 1177, 2019/02

https://doi.org/10.1002/ejic.201900016

Neutron diffraction measurements of an aqueous 2 mol dm CaCl solutions in DO have been made at 1 GPa, 298 K as well as 0.1 MPa, 298 K. The experimental structure factors are subjected to Empirical Potential Structure Refinement (EPSR) modeling to reveal the ion hydration and association and solvent water at the atomic level. About seven water molecules surround Ca at the Ca-O and Ca-D distances of 2.44 and 3.70 , respectively, at both pressures, suggesting no significant pressure effect on the cation hydration. On the other hand, the Cl ion shows a drastic change in water oxygen coordination from 7 at 0.1 MPa to 14 at 1 GPa, accompanied by shortening of Cl-O distance from 3.18 to 3.15 . However, the number of water hydrogen atoms around Cl does not change significantly as 6.0 6.7 with shortening Cl-D distance from 2.22 to 2.18 on compression. The pressure effect on the solvent water structure is also drastic as an increase in water oxygen atoms of 4.7 at the O-O distance of 2.79 at 0.1 MPa to 10.3 at 2.85 at 1 GPa. The number of water hydrogen atoms, however, does not change as 1.2 at the O-D distance of 1.74 for both pressures, demonstrating the presence of the OD hydrogen bonds which are significantly bent at 1 GPa at 298 K. This change of hydrogen bonds in water with pressure probably causes the drastic increase in water oxygen atoms around Cl.

Annual report on the effluent control of low level liquid waste in Nuclear Fuel Cycle Engineering Laboratories FY2015

Nakano, Masanao; Fujita, Hiroki; Kono, Takahiko; Nagaoka, Mika; Inoue, Kazumi; Yoshii, Hideki*; Otani, Kazunori*; Hiyama, Yoshinori*; Kikuchi, Masaaki*; Sakauchi, Nobuyuki*; et al.

JAEA-Review 2017-001, 115 Pages, 2017/03

JAEA-Review-2017-001.pdf:3.57MB

Based on the regulations (the safety regulation of Tokai reprocessing plant, the safety regulation of nuclear fuel material usage facilities, the radiation safety rule, the regulation about prevention from radiation hazards due to radioisotopes, which are related with the nuclear regulatory acts, the local agreement concerning with safety and environment conservation around nuclear facilities, the water pollution control law, and bylaw of Ibaraki prefecture), the effluent control of liquid waste discharged from the Nuclear Fuel Cycle Engineering Laboratories of Japan Atomic Energy Agency has been performed. This report describes the effluent control results of the liquid waste in the fiscal year 2015. In this period, the concentrations and the quantities of the radioactivity in liquid waste discharged from the reprocessing plant, the plutonium fuel fabrication facilities, and the other nuclear fuel material usage facilities were much lower than the limits authorized by the above regulations.

User manual of Soil and Cesium Transport (SACT), a program to predict long-term Cs distribution using USLE for soil erosion, transportation and deposition

Saito, Hiroshi; Yamaguchi, Masaaki; Kitamura, Akihiro

JAEA-Testing 2016-003, 68 Pages, 2016/12

JAEA-Testing-2016-003.pdf:6.4MB

JAEA has developed a simple and fast simulation program "SACT" (Soil and Cesium Transport) to predict a long-term distribution of Cs deposited on the land surface due to the Fukushima Daiichi Nuclear Power Station accident. It calculates soil movement (erosion, transportation, deposition) and Cs migration, and predicts its future distribution with the assumption that it is adhered to soil. SACT uses USLE (Universal Soil Loss Equation) for potential soil loss and simple equations for soil transportation and deposition. The Cs amount is predicted by the amount of soil movement and Cs concentration ratio for each grain-size of soil. SACT is characterized by its simplicity which enables fast calculation for wide area for long-term duration using existing equations. Data for parameters are widely available and site-specific calculations are possible using data of the targeted area. This manual provides useful and necessary information to users and facilitates the use of SACT widely.

Sediment and Cs transport and accumulation in the Ogaki Dam of eastern Fukushima

Yamada, Susumu; Kitamura, Akihiro; Kurikami, Hiroshi; Yamaguchi, Masaaki; Malins, A.; Machida, Masahiko

Environmental Research Letters, 10(1), p.014013_1 - 014013_9, 2015/01

https://doi.org/10.1088/1748-9326/10/1/014013

The Ogaki Dam Reservoir is one of the principal irrigation dam reservoirs in the Fukushima Prefecture and its upstream river basin was heavily contaminated by radioactivity from the Fukushima Daiichi Nuclear Power Plant accident. For the purpose of environmental assessment, it is important to determine the present condition of the water in the reservoir and to understand the behavior of sediment-sorbed radioactive cesium under different modes of operation of the dam. This paper addresses this issue with numerical simulations of fluvial processes in the reservoir using the 2D simulation code Nays2D. We present results for sediment deposition on the reservoir bed and the discharge via the dam under typical yearly flood conditions. The simulations show that almost all the sand and silt that enter into the reservoir deposit onto the reservoir bed. However, the locations where they tend to deposit differ, with sand tending to deposit close to the entrance of the reservoir, whereas silt deposits throughout the reservoir. Both sand and silt settle within a few hours of entering the reservoir. In contrast, clay remains suspended in the reservoir water for a period as long as several days, thus increasing the amount that is discharged downstream from the reservoir. Under the current operating mode of the dam, about three-quarters of clay that enters the reservoir during the flood is discharged downstream. By raising the height of the dam exit, the amount of clay exiting the reservoir can be reduced by a factor of three. The results indicate that the dam can be operated to buffer radioactive cesium and limit the contamination spreading into lowland areas of the Ukedo River basin. These results should be a factor in considerations for the future operation of the Ogaki Dam, and will be of interest for other operators of dam reservoirs in areas contaminated by radioactive fallout.

Predicting the long-term Cs distribution in Fukushima after the Fukushima Dai-ichi Nuclear Power Plant accident; A Parameter sensitivity analysis

Yamaguchi, Masaaki; Kitamura, Akihiro; Oda, Yoshihiro; Onishi, Yasuo*

Journal of Environmental Radioactivity, 135, p.135 - 146, 2014/09

https://doi.org/10.1016/j.jenvrad.2014.04.011

We applied a model, to predict long term cesium distribution on Fukushima area, based on the USLE and simple sediment discharge formulas. Sensitivity analysis was conducted here to narrow the range of the output results due to the uncertainties of parameters. The preliminary calculation indicated significant deposition of sand portion within river basins. On the other hand the most of the eroded silt and clay portions were transported downstream to the river mouths. Annual sediment outflow into the ocean from Abukuma River and its total from the other 13 river basins vary between calculation cases based on the variation of land use, landform or precipitation. On the other hand, contributions of those parameters are relatively small for Cs concentration within transported soil. This indicates the total amount of Cs outflow into the ocean could be controlled by amount of soil erosion and transport, and total amount of Cs remaining within the basin.

Predicting sediment and cesium-137 discharge from catchments in eastern Fukushima

Kitamura, Akihiro; Yamaguchi, Masaaki; Kurikami, Hiroshi; Yui, Mikazu; Onishi, Yasuo*

Anthropocene, 5, p.22 - 31, 2014/03

https://doi.org/10.1016/j.ancene.2014.07.001

Amount of soil and cesium losses in Eastern Fukushima Prefecture is evaluated by a simple and fast simulation model which we developed utilizing the universal soil loss equation and the geographical information system. We focused on the land use factor of the universal soil loss equation in this study. It was estimated that the forest occupies 64% of the total land surface of the study area, but only accounts for 24% of total soil runoff and 33% of total cesium dispersion. The most contributing component comes from the crop field, while the forest becomes the second. Also, calculation was performed for each river basins and results were compared with field monitoring data.

Simulating long-term Cs distribution on territory of Fukushima

Kitamura, Akihiro; Yamaguchi, Masaaki; Oda, Yoshihiro; Kurikami, Hiroshi; Onishi, Yasuo*

Transactions of the American Nuclear Society, 109(1), p.153 - 155, 2013/11

Long term Cs transport and its future distribution on the territory of Fukushima were predicted based on the USLE and the GIS. By modeling the soil erosion, transport, and deposition, we simulated the future distributions of air dose rates of Cs in mSv/h for 2, 6 and 21 years after the accident. The predictions made by METI were compared with the present results. The predictions of relatively high air dose rate areas were consistently matched between the two models over time. However, our model seemed to predict the decreasing rate of the Cs concentration with time to be slightly less than that of METI prediction. Some portions of the results obtained in the present study were used to provide influxes of sediments and Cs as boundary conditions and lateral inflows for the hydraulic river model.