Mathematical Modeling of Radioactive Contaminants in the Fukushima Environment

Kitamura, Akihiro; Kurikami, Hiroshi; Yamaguchi, Masaaki; Oda, Yoshihiro; Saito, Tatsuo; Kato, Tomoko; Niizato, Tadafumi; Iijima, Kazuki; Sato, Haruo; Yui, Mikazu; et al.

Nuclear Science and Engineering, 179(1), p.104 - 118, 2015/01

https://doi.org/10.13182/NSE13-89

The prediction of the distribution and fate of radioactive materials eventually deposited at surface in the Fukushima area is one of the main objectives and expected to be achieved in an efficient manner. In order to make such prediction, a number of mathematical models of radioactive contaminants, with particular attention on cesium, on the land and in rivers, lakes, and estuaries in the Fukushima area are developed. Simulation results are examined with the field investigations simultaneously implemented. The basic studies of the adsorption/absorption mechanism of cesium and soils have been performed to shed light on estimating distribution coefficient between dissolved contaminant and particulate contaminant.

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.

Decontamination of school facilities in Fukushima-city

Yoshikawa, Hideki; Iijima, Kazuki; Sasamoto, Hiroshi; Fujiwara, Kenso; Mitsui, Seiichiro; Kitamura, Akira; Kurikami, Hiroshi; Tokizawa, Takayuki; Yui, Mikazu; Nakayama, Shinichi

Materials Research Society Symposium Proceedings, Vol.1518, p.269 - 275, 2013/10

https://doi.org/10.1557/opl.2013.75

Following the release of radionuclides into the environment as a result of the accident at Fukushima Daiichi Nuclear Power Plant, Japan Atomic Energy Agency (JAEA) had to develop an immediate and effective method of reducing the dose rate received by students in school facilities. A demonstration of a reducing method was carried out by JAEA at a junior high school ground and kindergarten yard in the center of Fukushima-city. Dose rates of the released radionuclides are largely controlled by the ground level contamination and accumulation of mainly cesium-137 (Cs) and cesium-134 (Cs) in populated areas. An effective means of reducing dose rate was to remove the surface soil and to bury it on-site under fresh uncontaminated soil or soil collected under deep depth at the site for shielding. The dose rate at1 m above ground level was reduced from 2.5 Sv/h to 0.15 Sv/h.

Development of a grout database for geological disposal of high-level radioactive waste

Tsuda, Hidenori; Walker, C.; Shinkai, Fumiaki*; Kishi, Hirokazu*; Yui, Mikazu

Journal of Nuclear Science and Technology, 49(11), p.1110 - 1113, 2012/11

https://doi.org/10.1080/00223131.2012.730901

Development of evaluation methodology for effects of cementitious grouting materials on groundwater and rock in fractured media

Sasamoto, Hiroshi; Yui, Mikazu; Takase, Hiroyasu*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 11(3), p.233 - 246, 2012/09

https://doi.org/10.3327/taesj.J11.038

Leachates from cementitious grouting materials used for reducing water-inflow are hyperalkaline and chemically reactive with the engineered barriers and host rock of deep repository of high level radioactive waste. Evaluation methods for long-term alteration of host rock have been developing since the extent of chemical modification may influence the transport and retardation properties of radionuclides in the far-field. Not only conventional Ordinary Portland Cement (OPC) but also low-pH (alkaline) cement (LoAC) has been considered as the grouting material in order to reduce the extent of alteration of host rock. Comparative simulations for long-term alteration of host rock considering both OPC and LoAC grouts are conducted to propose an idea for evaluation of applicability of cementitious grouting materials from view points of reducing uncertainty and conservatism of safety assessment.

Investigation on geochemical influence of grout material on groundwater

Matsui, Hiroya; Mizuno, Takashi; Sasamoto, Hiroshi; Sugihara, Kozo; Yui, Mikazu

Dai-41-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.179 - 184, 2012/01

Japan Atomic Energy Agency has been conducted a contract study with METI (Ministry of Economy, Trade and Industry) called "The project for Grouting Technology Development" since 2008. As a part of the study, the monitoring of groundwater chemistry in a pre-grouted area has been carried out for three and half years after pre-grouting in Mizunami URL. The results suggested that the chemical compositions in groundwater affected by pre-grouting was recovered and the period to recover is evaluated about two years around an underground opening.

Diffusion and sorption of Cs, I and HTO in samples of the argillaceous Wakkanai Formation from the Horonobe URL, Japan; Clay-based modeling approach

Tachi, Yukio; Yotsuji, Kenji; Seida, Yoshimi*; Yui, Mikazu

Geochimica et Cosmochimica Acta, 75(22), p.6742 - 6759, 2011/11

https://doi.org/10.1016/j.gca.2011.08.039

Diffusion and sorption behaviors of Cs, I and HTO in samples of the Wakkanai Formation from Horonobe URL were investigated as a function of ionic strength (IS) of synthetic groundwater by through-diffusion and batch sorption experiments. The values showed cation excess and anion exclusion effects, which were strongly dependent on IS; for Cs decreased as IS increased, for I showed the opposite dependency and for HTO showed no dependence. The Kd values for Cs determined by through-diffusion and batch experiments were in good agreement and decreased with IS as a result of competitive ion exchange. Diffusion and sorption behaviors were interpreted based on the clay-based modeling approach in assuming the clay components of illite and smectite control diffusion and sorption mechanisms. The model predicted the and Kd trends obtained by the series of experiments reasonably well, implying the key contribution of the clay particle and nano-size pore for ionic migration.

Development of mechanistic sorption model and treatment of uncertainties for Ni sorption on montmorillonite/bentonite

Ochs, M.*; Tachi, Yukio; Ganter, C.*; Suyama, Tadahiro; Yui, Mikazu

JAEA-Research 2010-052, 59 Pages, 2011/02

JAEA-Research-2010-052.pdf:1.1MB

For reliable parameter setting in performance assessment of geological disposal, JAEA has developed the integrated sorption and diffusion (ISD) model/database in bentonite systems. The main goal of the mechanistic model/database development is to provide a tool for a consistent explanation, prediction, and uncertainty assessment. This report focuses on developing the thermodynamic sorption model (TSM) including selection of model design and surface species, and on the quantification and handling of model uncertainties, based on illustrating by example of Ni sorption on montmorillonite/bentonite. Two fundamentally different approaches are presented and compared for representing TSM uncertainties: (1) TSM parameter uncertainties based on optimization routines and statistical procedure, (2) overall error estimated by direct comparison of modeled and experimental Kd values. The overall error in Kd is viewed as the best representation of model uncertainty in ISD model/database development.

Sorption and diffusion of Eu in sedimentary rock in the presence of humic substance

Seida, Yoshimi; Terashima, Motoki; Tachi, Yukio; Iijima, Kazuki; Nakazawa, Toshiyuki*; Yamada, Norikazu*; Yui, Mikazu

Radiochimica Acta, 98(9-11), p.703 - 709, 2010/11

https://doi.org/10.1524/ract.2010.1771

Diffusion and sorption behaviors of Eu in sedimentary rock were investigated in the presence of humic substance in the present study. Sedimentary rock obtained from Horonobe URL test site in Hokkaido, Japan, (accessible pore diameter is around several to several ten nanometer) was used. The Diffusion behaviors of Eu were examined based on reservoir depletion method coupled with analysis of inner distribution of the radioactive elements in the rock. Time sequence of concentration of each radioactive element as well as the humic substance in the reservoir was obtained as a function of concentration and molecular size of humic substance. Coexistence of humic substance reduced the depletion of Eu in the reservoir, indicating complexation between the radioactive elements and the humic substance. On the contrary, obvious decrease of humic substance in the reservoir was not observed in the system. This observation suggests that the radioactive elements became hard to diffuse into the sedimentary rock due to an increase of their size through complexation with the humic substance. The sorption of Eu was reduced with increase of the humic substance although the sorption of the humic substance was not influenced by the existence of Th or Eu. The diffusion and sorption of Eu were found to be reduced in the presence of humic substance.

Information basis for developing comprehensive waste management system; US-Japan Joint Nuclear Energy Action Plan Waste Management Working Group Phase I report (Joint research)

Yui, Mikazu; Ishikawa, Hirohisa; Watanabe, Atsuo*; Yoshino, Kyoji*; Umeki, Hiroyuki; Hioki, Kazumasa; Naito, Morimasa; Seo, Toshihiro; Makino, Hitoshi; Oda, Chie; et al.

JAEA-Research 2010-015, 106 Pages, 2010/05

JAEA-Research-2010-015.pdf:13.58MB

This report summarizes the activity of Phase I of Waste Management Working Group of the United States - Japan Joint Nuclear Energy Action Plan started in 2007. The working group focused on consolidation of the existing technical basis between the U.S. and Japan and the joint development of a plan for future collaborative activities. Firstly, the political/regulatory frameworks related to nuclear fuel cycles in both countries were reviewed. The various advanced fuel cycle scenarios in both countries were surveyed and summarized. Secondly, the waste management/disposal system optimization was discussed. Repository system concepts for the various classifications of nuclear waste were reviewed and summarized, then disposal system optimization processes and techniques were reviewed, and factors to consider in future repository design optimization activities were also discussed. Finally the potential collaboration areas and activities related to the optimization problem were extracted.