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Journal Articles

Experimental additive manufacturing of green body of SiC/Graphite functionally graded materials by stereolithography

Ueta, Shohei; Imai, Yoshiyuki; Watanabe, Masashi; Segawa, Tomoomi; Yan, X.

International Journal of Applied Ceramic Technology, 20(1), p.261 - 265, 2023/01

 Times Cited Count:2 Percentile:25.30(Materials Science, Ceramics)

Journal Articles

Prediction of critical heat flux for the forced convective boiling based on the mechanism

Ono, Ayako; Sakashita, Hiroto*; Yamashita, Susumu; Suzuki, Takayuki*; Yoshida, Hiroyuki

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 7 Pages, 2022/10

The new prediction method of critical heat flux (CHF) of the fuel assemblies based on the mechanism is proposed in this study. The prediction method of CHF based on the mechanism has been needed for a long time to enhance the safety analysis and reduce the design cost. From several experimental findings of the liquid-vapor behavior near the heating surface from the nucleate boiling to the CHF, the authors consider that the macrolayer dryout model will be appropriate to predict the CHF under the reactor condition. The prediction method of the macrolayer thickness and the passage period of vapor mass in the fuel assemblies are needed to predict CHF from the macrolayer dryout model. In this study, the CHF under the forced convection is evaluated by combining the prediction methods for the macrolayer thickness and passage period of vapor mass, which are proposed by authors. The prediction of the CHF under the forced convection is examined and compared with the experimental data.

Journal Articles

Effects of a corrosion inhibitor on the corrosion of steels under thin solution layers

Momma, Yuichiro*; Sakairi, Masatoshi*; Ueno, Fumiyoshi; Otani, Kyohei

Zairyo To Kankyo, 71(5), p.133 - 137, 2022/05

The effect of the corrosion inhibitor on the corrosion of steel under a thin solution layer was investigated. As a result of forming a thin solution layer with a thickness of 1.0-0.2 mm on the specimen, adding a mixed solution of sodium molybdate and aluminum lactate as a corrosion inhibitor, and performing electrochemical measurement, the corrosion inhibitor suppresses the anodic reaction. And in the thin solution layer, it was suggested that the morphology of the protective layer structure by the corrosion inhibitor changed according to the amount of liquid as compared with the bulk immersion.

Journal Articles

Tracer diffusion coefficients measurements on LaPO$$_{4}$$-dispersed LATP by means of neutron radiography

Song, F.*; Chen, H.*; Hayashida, Hirotoshi*; Kai, Tetsuya; Shinohara, Takenao; Yabutsuka, Takeshi*; Yao, Takeshi*; Takai, Shigeomi*

Solid State Ionics, 377, p.115873_1 - 115873_6, 2022/04

 Times Cited Count:2 Percentile:27.26(Chemistry, Physical)

Journal Articles

Electrochemical behavior of carbon steels under thickness-controlled solution layer

Momma, Yuichiro*; Sakairi, Masatoshi*; Ueno, Fumiyoshi; Otani, Kyohei

Zairyo To Kankyo, 71(4), p.121 - 125, 2022/04

The effect of solution layer thickness on the atmospheric corrosion of carbon steel was investigated using novel devices fabricated by a 3D printer. These novel devices allowed us to control the solution layer thickness precisely. Potentiodynamic polarization measurements were performed under thickness-controlled solution layer, and oxygen diffusion limiting current density ($$j_{rm lim}$$) and anodic current density ($$j_{rm anode}$$) were measured. As the solution layer become thinner, $$j_{rm lim}$$ increased and $$j_{rm anode}$$ decreased. This result indicates that corrosion accelerates when the solution layer becomes thinner. The diffusion coefficient of oxygen was calculated as 3.20$$times$$10$$^{-5}$$ cm$$^{2}$$ s$$^{-1}$$ from the relationship between $$j_{rm lim}$$ and solution layer thickness, and the critical diffusion thickness was estimated to be 0.87 mm.

Journal Articles

Toward mechanistic evaluation of critical heat flux in nuclear reactors, 2; Recent studies and future challenges toward mechanistic and reliable CHF evaluation

Okawa, Tomio*; Mori, Shoji*; Liu, W.*; Ose, Yasuo*; Yoshida, Hiroyuki; Ono, Ayako

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 63(12), p.820 - 824, 2021/12

The evaluation method of the critical heat flux based on the mechanism is needed for the efficient design and development of fuel in reactors and the appropriate safety evaluation. In this paper, the current researches relating to the mechanism of the critical heat flux are reviewed, and the issue to be considered in the future are discussed.

Journal Articles

Effect of interlayer cations on montmorillonite swelling; Comparison between molecular dynamic simulations and experiments

Yotsuji, Kenji*; Tachi, Yukio; Sakuma, Hiroshi*; Kawamura, Katsuyuki*

Applied Clay Science, 204, p.106034_1 - 106034_13, 2021/04

 Times Cited Count:65 Percentile:99.71(Chemistry, Physical)

Journal Articles

Macrolayer formation model for prediction of critical heat flux in saturated and subcooled pool boiling

Ono, Ayako; Sakashita, Hiroto*; Yoshida, Hiroyuki

Heat Transfer Engineering, 42(21), p.1775 - 1788, 2021/00

 Times Cited Count:3 Percentile:22.23(Thermodynamics)

In this study, the macrolayer formation model is proposed to predict the critical heat flux in the saturated and subcooled pool boiling based on the macrolayer dryout model. This model concept is based on the results of the previous experiments. In the model, the nucleation site is assumed to distribute based on the Poisson distribution. Combining the proposed macrolayer formation model and macrolayer dryout model, the CHFs up to subcooling 40K were predicted and they are successfully good agreement with the experimental data. Moreover, the concept of the model was confirmed by the numerical simulation using the TPFIT.

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

 Times Cited Count:13 Percentile:48.08(Environmental Sciences)

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

Experimental evaluation of wall shear stress in a double contraction nozzle using a water mock-up of a liquid Li target for an intense fusion neutron source

Kondo, Hiroo*; Kanemura, Takuji*; Park, C. H.*; Oyaizu, Makoto*; Hirakawa, Yasushi; Furukawa, Tomohiro

Fusion Engineering and Design, 146(Part A), p.285 - 288, 2019/09

 Times Cited Count:1 Percentile:10.65(Nuclear Science & Technology)

Herein, the wall shear stress in a double contraction nozzle has been evaluated experimentally to produce a liquid lithium (Li) target as a beam target for intense fusion neutron sources such as the International Fusion Materials Irradiation Facility (IFMIF), the Advanced Fusion Neutron Source (A-FNS), and the DEMO Oriented Neutron Source (DONES). The boundary layer thickness and wall shear stress are essential physical parameters to understand erosion-corrosion by the high-speed liquid Li flow in the nozzle, which is the key component in producing a stable Li target. Therefore, these parameters were experimentally evaluated using an acrylic mock-up of the target assembly. The velocity distribution in the nozzle was measured by a laser-doppler velocimeter and the momentum thickness along the nozzle wall was calculated using an empirical prediction method. The resulting momentum thickness was used to estimate the variation of the wall shear stress along the nozzle wall. Consequently, the wall shear stress was at the maximum in the second convergent section in front of the nozzle exit.

Journal Articles

Synergetic strengthening of layered steel sheet investigated using an ${it in situ}$ neutron diffraction tensile test

Kim, J. G.*; Bae, J. W.*; Park, J. M.*; Woo, W.*; Harjo, S.; Chin, K.-G.*; Lee, S.*; Kim, H. S.*

Scientific Reports (Internet), 9, p.6829_1 - 6829_7, 2019/05

 Times Cited Count:14 Percentile:52.74(Multidisciplinary Sciences)

Journal Articles

Numerical study on effect of nucleation site density on behavior of bubble coalescence by using CMFD simulation code TPFIT

Ono, Ayako; Suzuki, Takayuki*; Yoshida, Hiroyuki

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 9 Pages, 2018/10

The mechanism of Critical Heat Flux (CHF) remains to be clarified, even though it is important to evaluate the CHF for super high heat flux components such as light water reactors (LWRs). Some theoretical models to predict the CHF is proposed so far. A macrolayer formation model which is proposed in order to predict the CHF based on the macrolayer dryout model. In this model, it is assumed that the liquid is captured inside vapor mass at coalescence. In this study, the verification of the assumption of a macrolayer formation model by the numerical simulation of CMFD code, TPFIT, from the view point of hydrodynamics.

Journal Articles

An Empirical model for the corrosion of stainless steel in BWR primary coolant

Uchida, Shunsuke*; Hanawa, Satoshi; Naito, Masanori*; Okada, Hidetoshi*; Lister, D. H.*

Corrosion Engineering, Science and Technology, 52(8), p.587 - 595, 2017/10

 Times Cited Count:4 Percentile:20.99(Materials Science, Multidisciplinary)

Based on the relationship among ECP, metal surface conditions, exposure time and other environmental conditions, a model to evaluate the ECP and corrosion rate of steel was developed by coupling a static electrochemical analysis and a dynamic oxide layer growth analysis. Major conclusion obtained on the model are as follows. The effect of H$$_{2}$$O$$_{2}$$ and O$$_{2}$$ concentrations on ECP were successfully explained as the effects of oxide layer growth. Hysteresis of ECP under changes in water chemistry conditions were successfully explained with the model. Decreases in ECP due to neutron exposure were explained well by radiation-induced diffusion in the oxide layers.

Journal Articles

Stability of montmorillonite edge faces studied using first-principles calculations

Sakuma, Hiroshi*; Tachi, Yukio; Yotsuji, Kenji; Suehara, Shigeru*; Arima, Tatsumi*; Fujii, Naoki*; Kawamura, Katsuyuki*; Honda, Akira

Clays and Clay Minerals, 65(4), p.252 - 272, 2017/08

 Times Cited Count:2 Percentile:16.39(Chemistry, Physical)

Structure and stability of montmorillonite edge faces (110), (010), (100), and (130) of the layer charges y = 0.5 and 0.33 are investigated by the first-principles electronic calculations based on the density functional theory. Stacking and single layer models are tested for understanding the effect of stacking on the stability of montmorillonite edge faces. Most stacking layers stabilize the edge faces by making hydrogen bonds between the layers; therefore, the surface energy of stacking layers is reduced rather than the single layer model. This indicates that the surface energy of edge faces should be estimated depending on the swelling conditions. Lowest surface energies of (010) and (130) edge faces were realized by the presence of Mg ions on the edge faces. These edge faces have a strong adsorption site for cations due to local negative charge of the edges.

Journal Articles

Chemical states of trace-level strontium adsorbed on layered oxide by XPS and XANES under total reflection condition

Baba, Yuji; Shimoyama, Iwao

Photon Factory Activity Report 2016, 2 Pages, 2017/00

In order to elucidate the adsorption states of radioactive Sr-90 in soil, chemical bonding states of non-radioactive strontium adsorbed on layered oxide (mica) have been investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy. Since the number of atoms in radioactive Sr-90 is extremely small, the XPS and XANES were measured under total reflection condition of the incident X-rays. The detection limit in total reflection XPS was about 150 pg/cm$$^{2}$$, which corresponds to 300 Bq of Sr-90. The Sr 2p$$_{3/2}$$ core-level energy in XPS shifted to lower energy with the decrease in the thickness of Sr layer. Also, the Sr 2p$$_{3/2}$$ $$rightarrow$$ Sr 4d$$^{*}$$ resonance energy in XANES shifts to lower energy with the decrease in the thickness. On the basis of a simple point charge model, it was elucidated that the chemical bond between Sr and mica surface becomes ionic with the decrease in the adsorbed amount of strontium.

JAEA Reports

Design study for impermeable function of trench disposal facility for very low level waste generated from research, industrial and medical facilities (Joint research)

Sakai, Akihiro; Kurosawa, Ryohei*; Nakata, Hisakazu; Okada, Shota; Izumo, Sari; Sato, Makoto*; Kitamura, Yoichi*; Honda, Yasutake*; Takaoka, Katsuki*; Amazawa, Hiroya

JAEA-Technology 2016-019, 134 Pages, 2016/10

JAEA-Technology-2016-019.pdf:8.25MB

Japan Atomic Energy Agency has been developing to design trench disposal facility with impermeable layers in order to dispose of miscellaneous waste. Geomembrane liners have a function that prevent seepage of leachant and collect the leachant. However, the geomembrane liners do not necessarily provide the expected performance due to damage generated when heavy equipment contacts with the liner. Therefore, we studied the impermeable layers having high performance of preventing seepage of leachant including radioactivity taking into account characteristics of low permeable materials and effect of multiple layer structure. As results, we have evaluated that the composite layers composed by a drainage layer, geomembrane liners and a low permeable layer are most effective structure to prevent seepage of leachant. Taking into account disposal of waste including cesium, we also considered zeolite containing sheets for adsorption of cesium were installed in the impermeable layers.

Journal Articles

Diffusion and adsorption of uranyl ion in clays; Molecular dynamics study

Arima, Tatsumi*; Idemitsu, Kazuya*; Inagaki, Yaohiro*; Kawamura, Katsuyuki*; Tachi, Yukio; Yotsuji, Kenji

Progress in Nuclear Energy, 92, p.286 - 297, 2016/09

 Times Cited Count:12 Percentile:74.16(Nuclear Science & Technology)

Diffusion and adsorption behavior of uranyl (UO$$_2^{2+}$$) species is important for the performance assessment of radioactive waste disposal. The diffusion behaviors of UO$$_2^{2+}$$, K$$^{+}$$, CO$$_3^{2-}$$ and Cl$$^{-}$$ and H$$_{2}$$O in the aqueous solutions were evaluated by molecular dynamics (MD) calculations. The diffusion coefficient (De) of UO$$_2^{2+}$$ is the smallest and is 26% less than the self-diffusion coefficient of H$$_{2}$$O. For the aqueous solution with high concentration of carbonate ions, uranyl carbonate complexes: UO$$_{2}$$CO$$_{3}$$ and UO$$_{2}$$(CO$$_{3}$$)$$^{2-}$$ can be observed. For the clay (montmorillonite or illite)-aqueous solution systems, the adsorption and diffusion behaviors of UO$$_2^{2+}$$ and K$$^{+}$$ were evaluated by MD calculations. The distribution coefficients (Kd) increase with the layer charge of clay, and Kd of UO$$_2^{2+}$$ might be smaller than that of K$$^{+}$$. Further, their two-dimensional diffusion coefficients were relatively small in the adsorption layer and were extremely small for illite with higher layer charge.

JAEA Reports

Effect of solid boric acid on the high temperature oxidation behavior of Zircaloy-4

Komiyama, Daisuke; Amaya, Masaki

JAEA-Research 2016-013, 20 Pages, 2016/08

JAEA-Research-2016-013.pdf:6.05MB

The boric acid in the coolant may precipitate on the fuel cladding surface in the case that the blockage of coolant flow path etc. occurs and/or the cooling of fuel becomes insufficient during a LOCA (Loss-Of-Coolant Accident) in PWRs. While there is much knowledge about the compatibility between Zircaloy-4 and boric acid under normal operation conditions, such knowledge under high temperature condition, e.g. LOCA, has not been sufficient. In this study, isothermal heating tests were carried out by using Zircaloy-4 plates with solid boric acid in various atmospheres at up to 900$$^{circ}$$C; and the stability of boric acid, the reaction between Zircaloy-4 and boric acid and the effect of solid boric acid on the high temperature oxidation behavior of Zircaloy-4 were investigated. From the results obtained, it was suggested that, if boric acid anhydride remained on the surface of Zircaloy-4, the boric acid anhydride prevented the surface of Zircaloy-4 from contacting oxidizing atmosphere and mitigated the high-temperature oxidation of Zircaloy-4. In the case that solid boric acid adhered to the surface of pre-oxidized Zircaloy-4 and they have been heated up to high temperature, it was indicated that the solid boric acid penetrated into the gaps in the pre-oxide layer and the penetrated solid boric acid mitigated the oxidation of Zircaloy-4 thereafter.

Journal Articles

Aperiodic multilayer structures in soft X-ray optics

Pirozhkov, A. S.; Ragozin, E. N.*

Physics-Uspekhi, 58(11), p.1095 - 1105, 2015/11

 Times Cited Count:29 Percentile:57.73(Physics, Multidisciplinary)

Journal Articles

First principles molecular dynamics study of interlayer water and cations in vermiculite

Ikeda, Takashi

Clay Science, 18(2), p.23 - 31, 2014/06

To clarify possible origins of irreversible adsorption exhibited by cesium on clay minerals, we performed FPMD simulations for vermiculite including water molecules along with Mg$$^{2+}$$, K$$^{+}$$, and Cs$$^{+}$$ in its interlayers. Our close examination on the structural and dynamical properties of interlayer water included together with the cations shows that Mg$$^{2+}$$ and Cs$$^{+}$$ form respectively outer- and inner-sphere surface complexes in the interlayers, while K$$^{+}$$ forms both types. The structure of electric double layers formed in the interlayers is found to depend significantly on the type of surface complexes of interlayer cations. The reorientational motions of H$$_{2}$$O are suggested to be enhanced by Cs$$^{+}$$ in contrast to a minor influence of Mg$$^{2+}$$ and K$$^{+}$$. Our observed enhanced diffusion of interlayer H$$_{2}$$O along with their rapid reorientation indicates that Cs$$^{+}$$ ions work as structure-breaking ions even in confined 2-dimensional interlayers.

159 (Records 1-20 displayed on this page)