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Journal Articles

Experimental study on local interfacial parameters in upward air-water bubbly flow in a vertical 6$$times$$6 rod bundle

Han, X.*; Shen, X.*; Yamamoto, Toshihiro*; Nakajima, Ken*; Sun, Haomin; Hibiki, Takashi*

International Journal of Heat and Mass Transfer, 144, p.118696_1 - 118696_19, 2019/12

Journal Articles

On the hydrogen production of geopolymer wasteforms under irradiation

Cantarel, V.; Arisaka, Makoto; Yamagishi, Isao

Journal of the American Ceramic Society, 102(12), p.7553 - 7563, 2019/12

The hydrogen gas (H$$_{2}$$) production of wasteforms is a major safety concern for encapsulating nuclear wastes. For geopolymers, the H$$_{2}$$ produced by radiolytic processes is a key factor because of the large amount of water present in their porous structure. Herein, the hydrogen production was measured under $$^{60}$$Co gamma irradiation. The effect of water saturation and sample size were studied for pure geopolymers, or using zeolites as an example waste. When geopolymer monolithic samples were large and saturated by water, the hydrogen released was measured up to two orders of magnitude lower with a 40 cm long cylinder samples (1.9$$times$$10$$^{-10}$$ mol.J$$^{-1}$$) than a sample in powder form (2.2$$times$$10$$^{-8}$$ mol.J$$^{-1}$$). To interpret results, a simple model was used, considering only hydrogen production, a potential recombination and its diffusion in the geopolymer matrix. Knowing the diffusion constant of the matrix, the model was able to reproduce the evolution of the hydrogen release as a function of the water saturation level and predict the evolution when sample size is increased up to 40 cm.

Journal Articles

Study on dryout and rewetting during accidents including ATWS for the BWR at JAEA

Satou, Akira; Wada, Yuki; Shibamoto, Yasuteru; Yonomoto, Taisuke

Nuclear Engineering and Design, 354, p.110164_1 - 110164_10, 2019/12

JAEA has conducted a series of experimental researches on the Post-boiling transition heat transfer, transient critical heat flux and rewetting for BWRs. Experimental data bases covering the anticipated operational conditions was developed; the significance of the precursor cooling was identified. This paper presents approaches of the present research focusing on the anticipated transient without scram, effects of the spacer and physical understanding of the phenomena for development of mechanistic model together with promising results obtained so far.

Journal Articles

Comparative methodology between actual RCCS and downscaled heat-removal test facility

Takamatsu, Kuniyoshi; Matsumoto, Tatsuya*; Liu, W.*; Morita, Koji*

Annals of Nuclear Energy, 133, p.830 - 836, 2019/11

A RCCS having passive safety features through radiation and natural convection was proposed. The RCCS design consists of two continuous closed regions: an ex-reactor pressure vessel region and a cooling region with a heat-transfer surface to ambient air. The RCCS uses a novel shape to remove efficiently the heat released from the RPV through as much radiation as possible. Employing air as the working fluid and ambient air as the ultimate heat sink, the RCCS design can strongly reduce the possibility of losing the working fluid and the heat sink for decay-heat-removal. Moreover, the authors started experiment research with using a scaled-down heat-removal test facility. Therefore, this study propose a comparative methodology between an actual RCCS and a scaled-down heat-removal test facility.

Journal Articles

Estimation of planes of a rock mass in a gallery wall from point cloud data based on MD PSO

Matsuura, Yuto*; Hayano, Akira; Itakura, Kenichi*; Suzuki, Yukinori*

Applied Soft Computing, 84, p.105737_1 - 105737_9, 2019/11

LiDAR (laser imaging detection and ranging) has been developed to obtain a high-resolution point cloud data indicating the detailed 3D shapes of an object. To identify discontinuities in a rock mass of a tunnel gallery wall, it is necessary to approximate the rock mass surface with small planes. Normal vectors of the planes are important to identify discontinuities. We developed an algorithm for estimation of planes based on multi-dimensional particle swarm optimization (MD PSO) from point cloud data. Point cloud data were segmented into bounding boxes and grouped into clusters by MD PSO. Planes were estimated using the least squares method for point cloud data in the respective clusters. The newly developed MD PSO algorithm was evaluated using point cloud data obtained from a gallery wall. Evaluation was carried out in comparison with the previous developed variable-box segmentation (VBS) algorithm. The MD PSO-based algorithm showed a 7% higher accuracy than that of the VBS algorithm.

Journal Articles

Thick-restart block Lanczos method for large-scale shell-model calculations

Shimizu, Noritaka*; Mizusaki, Takahiro*; Utsuno, Yutaka; Tsunoda, Yusuke*

Computer Physics Communications, 244, p.372 - 384, 2019/11

no abstracts in English

Journal Articles

Short- and middle-ranges order structures of KNbO$$_3$$ nanocrystals

Yoneda, Yasuhiro; Kunisada, Ryoichi*; Chikada, Tsukasa*; Ueno, Shintaro*; Fujii, Ichiro*; Nagata, Hajime*; Ohara, Koji*; Wada, Satoshi*

Japanese Journal of Applied Physics, 58(SL), p.SLLA03_1 - SLLA03_7, 2019/11

Journal Articles

Thermodynamic interpretation of uranium(IV/VI) solubility in the presence of $$alpha$$-isosaccharinic acid

Kobayashi, Taishi*; Sasaki, Takayuki*; Kitamura, Akira

Journal of Chemical Thermodynamics, 138, p.151 - 158, 2019/11

The effect of $$alpha$$-isosaccharinic acid (ISA) on the solubility and redox of tetravalent and hexavalent uranium (U(IV), U(VI)) was investigated in the hydrogen ion concentration (pH$$_{c}$$) range of 6$$sim$$13 and at total ISA concentration ([ISA]$$_{rm tot}$$) = 10$$^{-4}$$$$sim$$10$$^{-1.2}$$ mol/dm$$^{3}$$. The dependence of U(IV) solubility on pH$$_{c}$$ and [ISA]$$_{rm tot}$$ suggested the existence of U(OH)$$_{4}$$(ISA)$$_{2}$$$$^{2-}$$ as a dominant species within the investigated pH$$_{c}$$ range of 6$$sim$$12. For the U(VI)-ISA system, UO$$_{2}$$(OH)$$_{3}$$(ISA)$$_{2}$$$$^{2-}$$ was suggested as a dominant species at pH$$_{c}$$ 7$$sim$$13. The formation constants of the U(IV)-ISA and U(VI)-ISA complexes were determined by least-squares fitting of the solubility data. The solubility of U(IV) and U(VI) in the presence of ISA and its effect on the redox behavior were thermodynamically interpreted based on the obtained constants.

Journal Articles

Numerical study of transport pathways of $$^{137}$$Cs from forests to freshwater fish living in mountain streams in Fukushima, Japan

Kurikami, Hiroshi; Sakuma, Kazuyuki; Malins, A.; Sasaki, Yoshito; Niizato, Tadafumi

Journal of Environmental Radioactivity, 208-209, p.106005_1 - 106005_11, 2019/11

To assess the uptake of Cs-137 ($$^{137}$$Cs) by freshwater fish, we developed a compartment model for the migration of $$^{137}$$Cs on the catchment scale from forests to river water. We modelled a generic forest catchment with Fukushima-like parameters to ascertain the importance of export pathways of $$^{137}$$Cs from forests to river water for the uptake of $$^{137}$$Cs by freshwater fish. The results suggest that the decreasing trend of $$^{137}$$Cs in river water and freshwater fish was due to combination of the decreasing trend in the forest leaves/needles and litter compartments, and the increasing trend in soil. The $$^{137}$$Cs concentrations within these forest compartments plateau at around ten years after the fallout due to $$^{137}$$Cs circulation in forests reaching an equilibrium state.

Journal Articles

Characterizing vertical migration of $$^{137}$$Cs in organic layer and mineral soil in Japanese forests; Four-year observation and model analysis

Muto, Kotomi; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Koarashi, Jun

Journal of Environmental Radioactivity, 208-209, p.106040_1 - 106040_10, 2019/11

Vertical distributions of $$^{137}$$Cs in the soil profile were observed at five forest sites with different vegetation types for 4.4 years after the Fukushima Dai-ichi Nuclear Power Plant accident, and $$^{137}$$Cs migration in the organic layer and mineral soil was analyzed based on a comparison of models and observations. Cesium-137 migration from the organic layer was faster than that observed in European forests, suggesting that the mobility and bioavailability of $$^{137}$$Cs could be suppressed rapidly in Japanese forests. The diffusion coefficients of $$^{137}$$Cs in the mineral soil were estimated to be 0.042-0.55 cm$$^2$$y$$^{-1}$$, which were roughly comparable with those of European forest soils affected by the Chernobyl Nuclear Power Plant accident. Model predictions indicated $$^{137}$$Cs mainly distributed in the surface mineral soil at 10 years after the accident. It suggest that the $$^{137}$$Cs deposited onto Japanese forest ecosystems will be retained in the surface layers of mineral soil for a long time.

Journal Articles

A Modeling approach to estimate the $$^{137}$$Cs discharge in rivers from immediately after the Fukushima accident until 2017

Sakuma, Kazuyuki; Nakanishi, Takahiro; Yoshimura, Kazuya; Kurikami, Hiroshi; Namba, Kenji*; Zheleznyak, M.*

Journal of Environmental Radioactivity, 208-209, p.106041_1 - 106041_12, 2019/11

We developed a simple model to evaluate and predict $$^{137}$$Cs discharge from catchment using tank model and L-Q equation. Using this model, $$^{137}$$Cs discharge and discharge ratio from Abukuma River and 13 other rivers in Fukushima coastal region were estimated from immediately after Fukushima accident to 2017. Cesium-137 discharge ratio to the deposition amount in catchment through Abukuma River and 13 other rivers in Fukushima coastal region during about initial six months were estimated to be 18 TBq (3.1%) and 11 TBq (0.8%), respectively. These values were 1-2 orders of magnitude larger than the previous study observed after June 2011, indicating that initial $$^{137}$$Cs discharge from catchment through rivers was a significant. However it was founded that an impact on the ocean derived from initial $$^{137}$$Cs discharge through river can be limited because $$^{137}$$Cs discharge from Abukuma River and 13 other rivers in Fukushima coastal region (29 TBq) was two orders of magnitude smaller than the direct release from FDNPP into the ocean (3.5 PBq) and from atmospheric deposition into the ocean (7.6 PBq).

JAEA Reports

On-site training using JMTR and related facilities in FY2018

Eguchi, Shohei; Nakano, Hiroko; Otsuka, Noriaki; Nishikata, Kaori; Nagata, Hiroshi; Ide, Hiroshi; Kusunoki, Tsuyoshi

JAEA-Review 2019-012, 22 Pages, 2019/10

JAEA-Review-2019-012.pdf:3.37MB

A practical training course using the JMTR and other research infrastructures was held from July 31st to August 7th in 2018 for Asian young researchers and engineers. This course was adopted as Japan-Asia Youth Exchange Program in Science (SAKURA Exchange Program in Science) which is the project of the Japan Science and Technology Agency, and this course aims to enlarge the number of high-level nuclear researchers/engineers in Asian countries which are planning to introduce a nuclear power plant, and to promote the use of facilities in future. In this year, 11 young researchers and engineers joined the course from 6 countries. This course consists of lectures, which are related to irradiation test research, safety management of nuclear reactors, nuclear characteristics of the nuclear reactors, etc., practical training such as practice of research reactor operation using simulator and technical tour of nuclear facilities on nuclear energy. The content of this course in FY 2018 is reported in this paper.

JAEA Reports

Annual report for FY2017 on the activities of Department of Decommissioning and Waste Management; April 1, 2017 - March 31, 2018

Department of Decommissioning and Waste Management

JAEA-Review 2019-011, 91 Pages, 2019/10

JAEA-Review-2019-011.pdf:5.25MB

This report describes the activities of Department of Decommissioning and Waste Management (DDWM) in Nuclear Science Research Institute (NSRI) in the period from April 1, 2017 to March 31, 2018. The report covers organization and missions of DDWM, outline and operation/maintenance of facilities which belong to DDWM, treatment and management of radioactive wastes, decommissioning activities, and related research and development activities which were conducted in DDWM.

JAEA Reports

Analysis of the radioactivity concentrations in low-level radioactive waste generated from JRR-2 and JRR-3 facilities

Haraga, Tomoko; Shimomura, Yusuke; Mitsukai, Akina; Ishimori, Kenichiro; Kameo, Yutaka

JAEA-Data/Code 2019-004, 48 Pages, 2019/10

JAEA-Data-Code-2019-004.pdf:4.67MB

In the future, radioactive wastes which generated from research and testing reactors in Japan Atomic Energy Agency are planning to be buried for the near surface disposal. Therefore, it is required to establish the method to evaluate the radioactivity concentrations of radioactive wastes by the time it starts disposal. In order to contribute to this work, we collected and analyzed the samples generated from JRR-2 and JRR-3. In this report, we summarized the radioactivity concentrations of 19 radionuclides ($$^{3}$$H, $$^{14}$$C, $$^{36}$$Cl, $$^{60}$$Co, $$^{63}$$Ni, $$^{90}$$Sr, $$^{94}$$Nb, $$^{99}$$Tc, $$^{rm 108m}$$Ag, $$^{129}$$I, $$^{137}$$Cs, $$^{152}$$Eu, $$^{154}$$Eu, $$^{234}$$U, $$^{238}$$U, $$^{238}$$Pu, $$^{239+240}$$Pu, $$^{241}$$Am, $$^{244}$$Cm) which were obtained from radiochemical analysis of those samples.

Journal Articles

Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability in clay barriers for the disposal of radioactive wastes

Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio

Applied Clay Science, 179, p.105146_1 - 105146_10, 2019/10

Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability was evaluated. Thermodynamic modeling using three different TDBs shows that stability fields for montmorillonite exist from 0 to 140$$^{circ}$$C, but at low values of silica activity, a stability field for illite replaces that for montmorillonite. Pore fluid chemical and mineralogical data for sediments from ODP sites from offshore Japan show a trend from montmorillonite + amorphous silica stability at temperatures up to 60$$^{circ}$$C to that for illite + quartz at higher temperatures. However, even over very long timescales ($$gg$$ 1 Ma), smectite does not transform to illite under thermodynamically-favourable conditions at temperatures less than 80$$^{circ}$$C.

Journal Articles

Temporal change in concentration of radiocesium in Fukushima river water

Nakanishi, Takahiro

Isotope News, (765), p.22 - 25, 2019/10

Temporal change in concentration of radiocesium in Fukushima river water are outlined. Radiocesium concentration in river water keeps decreasing after several years, however, the declining trend for the dissolved radiocesium concentration is gradually decreasing with time.

Journal Articles

Research and development behind a computation system for 3D distributions of air dose rates in the environment; Estimating environmental radiation doses using PHITS together with remote sensing data

Kim, M.; Malins, A.; Sakuma, Kazuyuki; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

Isotope News, (765), p.30 - 33, 2019/10

Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The $$^{134}$$Cs and $$^{137}$$Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, individual conifer and broadleaf trees, and the topography of the land surface. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Journal Articles

Dielectric and magnetocaloric study of TmCrO$$_{3}$$

Yoshii, Kenji; Ikeda, Naoshi*

Journal of Alloys and Compounds, 804, p.364 - 369, 2019/10

Dielectric and magnetocaloric measurements are carried out for the chromite TmCrO$$_{3}$$. This oxide was reported to be multiferroic below the N$'e$el temperature ($$T_{rm N}$$) of 125 K, likely due to a structural transformation. The dielectric response shows large dielectric constants below 300 K. However, from the analyses of loss tangent, AC conductivity and dielectric modulus, this behavior is rooted in hopping of charge carriers rather than electric dipoles, as proposed for some other chromites. No dielectric anomaly is found at $$T_{rm N}$$. The magnetocaloric effect shows that the magnetic transitions at $$T_{rm N}$$ as well as the spin reorientation temperature are of a second order. This result strongly suggests the absence of magnetostructural transition at $$T_{rm N}$$ in accord with no observation of ferroelectric transition at this temperature.

Journal Articles

Intense chemical weathering in southwest Japan during the Pliocene warm period

Hatano, Nozomi*; Yoshida, Koki*; Adachi, Yoshiko*; Sasao, Eiji

Journal of Asian Earth Sciences, 184, p.103971_1 - 103971_13, 2019/10

Whole rock major and REE geochemistry and mineral compositions of the Pliocene sediments in southwest Japan reveal the effects of source rock compositions and grain sizes, as well as the relationship between sedimentary environments and the degree of chemical weathering in the Pliocene warm period. A wide variation in the degree of chemical weathering, source rock compositions and grain sizes were observed with vertical and spatial changes in the sedimentary environment. Regardless of the wide variety of source rock compositions and grain sizes, REE and kaolinite-rich clay mineral concentrations in sediments, of which CIA values are generally above 90, are indicative of the intense weathering conditions that prevailed in the Pliocene period (3-4 Ma) in southwest Japan.

106340 (Records 1-20 displayed on this page)