Tachi, Yukio; Saito, Takumi*; Kirishima, Akira*
Nihon Genshiryoku Gakkai-Shi ATOMO, 64(5), p.290 - 295, 2022/05
no abstracts in English
Kirishima, Akira*; Terasaki, Mariko*; Miyakawa, Kazuya; Okamoto, Yoshihiro; Akiyama, Daisuke*
Chemosphere, 289, p.133181_1 - 133181_12, 2022/04
no abstracts in English
Hiroka, Shun; Yokoyama, Keisuke; Kato, Masato
Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Sustainable Clean Energy for the Future (FR22) (Internet), 8 Pages, 2022/04
Property studies on Am/Np-bearing MOX were carried out and how the properties influences on the irradiation behaviors was discussed. Both Am and Np inclusions increase the oxygen potential of MOX. Inter-diffusion coefficients obtained by using diffusion couple technique indicate that the inter-diffusion coefficient is larger in the order of U-Am, U-Pu and U-Np. Also, the inter-diffusion coefficients were evaluated to be larger at the O/M = 2 than those of O/M 2 by several orders. The increase of oxygen potential with Am/Np leads to higher vapor pressure of UO and the acceleration of the pore migration along temperature gradient during irradiation. The redistributions of actinide elements were also considered with the relationship of the pore migration and diffusion in solid state. Thus, the obtained inter-diffusion coefficients directly influence on the redistribution rate. The obtained properties were modelled and can be installed in a fuel irradiation simulation code.
Miwa, Kazuji; Namekawa, Masakazu*; Shimada, Taro; Takeda, Seiji
MRS Advances (Internet), 7(7-8), p.165 - 169, 2022/03
We have developed evaluation method of radiocesium (RCs) migration by surface runoff and soil erosion in considering vertical distribution of RCs in initial contaminated soil and concentration of RCs in different particle size. RCs migration on ground surface during single year has been evaluated in virtual site contaminated uniformly by Cs-137. As a result, RCs has concentrated in the impoundment, and 0.18% of total inventory in the site migrated into the sea. These results suggest that surface migration of RCs effects increasing of external exposure at impoundment and internal exposure from ingestion of marine product.
Chikyu Kagaku, 55(4), p.176 - 192, 2021/12
Iodine 129 (I) is a radionuclide that decays to Xe with a half-life of 15.7 million years. The analysis of I in the environment has played an important role not only in the fields of planetary science and earth science, but also in the nuclear field in recent years. Particularly, in the case of the Fukushima Dai-ichi Nuclear Power Plant accident in March, 2011, the scientists estimated the distribution and soil deposition of I over a wide area, and contributed to the assessment of internal exposure doses in the early stage of the accident. This is one of the most significant achievements in recent I-related studies. Future studies are expected to be conducted to elucidate the transport mechanism of I from land to river and sea, and to investigate the possible accumulation of I in aquatic organisms. The mobility of I in the soil studied by the author during the 10-years since the accident has been mainly reviewed in this manuscript.
Tachi, Yukio; Ito, Tsuyoshi*; Gylling, B.*
Water Resources Research, 57(11), 20 Pages, 2021/11
This paper focuses on the scaling approach for sorption and diffusion parameters from laboratory to in-situ conditions using the dataset of LTDE-SD experiment performed at the sp HRL. The near-surface heterogeneities at both fracture surface and rock matrix could be evaluated by conceptual model with high porosity and diffusivity, and sorption capacity, and their gradual change at the near-surface zones. The modelling results for non-sorbing Cl-36 and weak-sorbing Na-22 could validate the model concept and the parameter estimation of porosity and diffusivity, by considering the disturbed zone of 5 mm thickness with gradual parameter changes. The De values of these cationic and anionic tracers showed typical cation excess and anion exclusion effects. The modelling results for high sorbing tracers (Cs-137, Ra-226, Ni-63 and Np-237) with different sorption mechanism could confirm the validity of the scaling approaches of Kd values as a function of particle size and their relation to the near-surface disturbances.
Igarashi, Go*; Haga, Kazuko*; Yamada, Kazuo*; Aihara, Haruka; Shibata, Atsuhiro; Koma, Yoshikazu; Maruyama, Ippei*
Journal of Advanced Concrete Technology, 19(9), p.950 - 976, 2021/09
Okita, Shoichiro; Fukaya, Yuji; Goto, Minoru
Journal of Nuclear Science and Technology, 58(1), p.9 - 16, 2021/01
Suppressing the kernel migration rates, which depend on both the fuel temperature and the fuel temperature gradient, under normal operation condition is quite important from the viewpoint of the fuel integrity for High Temperature Gas-cooled Reactors. The presence of the ideal axial power distribution to minimize the maximum kernel migration rate allows us to improve efficiency of design work. Therefore, we propose a new method based on Lagrange multiplier method in consideration of thermohydraulic design in order to obtain the ideal axial power distribution to minimize the maximum kernel migration rate. For one of the existing conceptual designs performed by JAEA, the maximum kernel migration rate for the power distribution to minimize the maximum kernel migration rate proposed in this study is lower by approximately 10% than that for the power distribution as a conventional design target to minimize the maximum fuel temperature.
Kinoshita, Norikazu*; Nagaoka, Mika; Nakanishi, Takashi*
Science of the Total Environment, 753, p.142087_1 - 142087_10, 2021/01
The distribution of the anthropogenic radionuclide americium-241 (Am), a decay product of Pu discharged from atmospheric tests of nuclear weapons, was investigated to resolve its horizontal and vertical migration in the Tropical East Pacific. We analyzed Am concentrations in seawater samples collected in 2003. On comparing the Am concentrations with the previously determined concentrations of Pu in the same samples, the vertical profiles of Am were found to be similar to those of Pu. At some stations, the maximum concentration of Am occurred 100-200 m deeper than that of Pu. The Am/Pu ratios in the North Pacific and South Pacific were comparable to one another, and were typical of the ratio for the Pacific. The Am distribution was influenced by the water mass at depths below 400 m. The Am data support the view there is a current flowing at depths of 400-3000 m from the North Pacific through the equator to the South Pacific. In addition, the Am vertical profile was explained by using a box model that considers the decay of Pu and adsorption and scavenging by suspended particles. The different depths for the maximum concentrations of Am and Pu observed at some stations were well explained by the model and by the distribution of CaCO particles. The residence time of Am in the Pacific was also estimated by using the model.
Saito, Kimiaki; Mikami, Satoshi; Ando, Masaki; Matsuda, Norihiro; Kinase, Sakae; Tsuda, Shuichi; Sato, Tetsuro*; Seki, Akiyuki; Sanada, Yukihisa; Wainwright-Murakami, Haruko*; et al.
Journal of Radiation Protection and Research, 44(4), p.128 - 148, 2019/12
Hamamoto, Takafumi*; Ishida, Keisuke*; Shibutani, Sanae*; Fujisaki, Kiyoshi*; Tachi, Yukio; Ishiguro, Katsuhiko*; McKinley, I. G.*
Proceedings of 2019 International High-Level Radioactive Waste Management Conference (IHLRWM 2019) (USB Flash Drive), p.77 - 82, 2019/04
Shimada, Taro; Takubo, Kazuya*; Takeda, Seiji; Yamaguchi, Tetsuji
Progress in Nuclear Science and Technology (Internet), 5, p.183 - 187, 2018/11
After fuel debris is removed from the reactor containment vessel at Fukushima Daiichi NPS (1F) and collected in waste containers in the future, the waste containers will be disposed at a deep geological repository. The uranium inventory and uranium-235 (U) enrichment of the fuel debris are larger than those of high-level vitrified wastes which are produced from liquid waste during reprocessing of spent nuclear fuels. Therefore, there is a possibility not to be excluded that a criticality occurs in the geological media where the uranium precipitates at the far-field from the repository, after the uranium located in the repository is dissolved by groundwater. In this study, we calculated the quantity of uranium precipitated at the natural barrier, and studied dimension of uranium deposited in the natural barrier and carried out the criticality analysis.
Tachi, Yukio; Ito, Tsuyoshi*; Akagi, Yosuke*; Sato, Hisao*; Martin, A. J.*
Water Resources Research, 54(11), p.9287 - 9305, 2018/11
Effects of fine-scale surface alterations on radionuclide migration in fractured crystalline rocks were investigated by a comprehensive approach coupling a series of laboratory tests, microscopic observations and modelling, using a single fractured granodiorite sample from the Grimsel Test Site, Switzerland. Laboratory tests including through-diffusion, batch sorption and flow-through tests using five tracers indicated that tracer retention was consistently in the sequence of HDO, Se, Cs, Ni, Eu, and as well as showing the existence of a diffusion-resistance layer near the fracture surface, cation excess and anion exclusion effects for diffusion. Microscale heterogeneities in structural properties around the fracture were clarified quantitatively by coupling X-ray CT and EPMA. A three layer model including weathered vermiculite, foliated mica and undisturbed matrix layers, and their properties such as porosity, sorption and diffusion parameters, could provide a reasonable interpretation for breakthrough curves and concentration distributions near fracture surface of all tracers, measured in flow-through tests.
Tsushima, Masahito*; Takeda, Masaki; Ono, Hirokazu
JAEA-Data/Code 2018-008, 78 Pages, 2018/10
Japan Atomic Energy Agency (JAEA) has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL). In-situ tracer migration test for fracture and matrix in the argillaceous rock, called for Wakkanai formation, has been conducted in the Horonobe URL project. This report summarizes data of borehole investigations and tracer migration test for fracture zone.
Takeda, Masaki; Ishii, Eiichi; Ono, Hirokazu; Kawate, Satoshi*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 25(1), p.3 - 14, 2018/06
Fault zones and excavation damaged zones have the potential to act as flow paths, and the characterization of solute transport in such zones in mudstones is important for the safe geological disposal of radioactive waste. However, few in situ tracer migration tests have been conducted on fractures in mudstones. The Japan Atomic Energy Agency has conducted in situ tracer migration experiments using uranine, for fractures in siliceous mudstone of the Wakkanai Formation. 18 experiments were conducted under various conditions An injection flow rate that is slightly higher than the pumping flow rate is ideal for tracer migration experiments involving injection and pumping, as conducted in this study. In situ tracer migration experiments involving injection and pumping conducted in a groundwater environment with dissolved gases allow empirical evaluation of the relationship of the tracer recovery ratio and the groundwater degassing with the injection and pumping flow rate ratio. This evaluation is effective for the design of experimental conditions that account for degassing and ensure high levels of tracer recovery.
Hamamoto, Takafumi*; Shibutani, Sanae*; Ishida, Keisuke*; Fujisaki, Kiyoshi*; Yamada, Motoyuki*; Tachi, Yukio
Proceedings of 6th East Asia Forum on Radwaste Management Conference (EAFORM 2017) (Internet), 6 Pages, 2017/12
NUMO has developed a generic safety case to demonstrate the feasibility and safety of geological disposal of HLW and TRU in Japan and to provide a basic structure for the safety case which will be applicable to any potential site. In this safety case, the safety assessment was carried out for the repositories tailored to site descriptive models developed for three representative rock groups (plutonic, Neogene sedimentary and Pre-Neogene sedimentary rocks). Radionuclide migration parameters in rocks, i.e. distribution coefficients (Kds) and effective diffusion coefficients (Des), were derived to allow safety analysis for a range of scenarios. In this generic stage, the values of these parameter were given as the statistical values derived from laboratory data for certain rock types. The data were extracted from the latest database, with interpretation based on radionuclide speciation derived from relevant groundwater thermodynamic modelings.
Transactions of the American Nuclear Society, 117(1), p.51 - 52, 2017/10
This presentation highlights JAEA's challenges for contributing to recovering the previous life of residents and the development of resilient communities in Fukushima Prefecture based on considering needs of local people on the environmental restoration categorized by the state of evacuation orders and the lifting of such orders.
Yotsuji, Kenji; Tachi, Yukio; Okubo, Takahiro*
CMS Workshop Lectures, Vol.21, p.251 - 257, 2016/06
We have developed integrated sorption and diffusion model (ISD model) for assessment of diffusion parameters consistent with sorption processes in compacted bentonite. The ISD model gives consistent consideration to porewater chemistry, sorption and diffusion processes in compacted bentonite. The diffusion component based on the electric double layer theory and the homogeneous pore model in the ISD model accounts consistently for cation De overestimation and anion exclusion in narrow pores. The current ISD model can quantitatively account for diffusion of monovalent cations and anions, however, the model predictions disagree with diffusion data for multivalent cation and complex species. To improve the applicability of the model, it is necessary to consider the atomic level interactions between solute, solvent or clay mineral, and try that we apply the current ISD model to heterogeneous pore structure. In this study we try the application of the current ISD model to multiple pore structure. As results of numerical analysis of these models, the salinity dependence of effective diffusivity for the multi-pore model is comparatively smaller than that for the homogeneous pore model and the current diffusion model is improved.
Kurikami, Hiroshi; Kitamura, Akihiro; Yamada, Susumu; Machida, Masahiko
Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05
Several numerical models have been prepared to deal with various time- and spatial-scale issues related to radioactive cesium migration in environment in Fukushima area. This paper describes fragments of the JAEA's approaches of modeling to deal with the issues corresponding to radioactive cesium migration in environment with some case studies.
Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 5 Pages, 2015/05
It is necessary to confirm that there is no significant radioactivity remaining on NPP site, for the site release beforehand. Cesium 137 (Cs) is the typical radionuclide caused from NPP. In this research, generation of particulate Cs species at ground surface and its migration behavior were examined. Migration experiments were carried out by a column method, in which deionized water was fed intermittently at the drying interval for 7 days into a sand layer contaminated with Cs. A portion of the Cs in the upper surface region, which formed particulate species by sorbing on fine particles, migrated into the deeper layer. Fine particle itself also was generated at the sand surface by weathering. The sand was weathered during the drying period, so that small amount of fine particles including Cs was newly dissociated from the sand. Such particulate Cs species may be accumulated slowly by repeated cycles of rainfall and drying, during long term.