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Journal Articles

Oxygen potential measurement of (U,Pu,Am)O$$_{2 pm x}$$ and (U,Pu,Am,Np)O$$_{2 pm x}$$

Hiroka, Shun; Matsumoto, Taku; Kato, Masato; Sunaoshi, Takeo*; Uno, Hiroki*; Yamada, Tadahisa*

Journal of Nuclear Materials, 542, p.152424_1 - 152424_9, 2020/12

 Times Cited Count:1 Percentile:39.17(Materials Science, Multidisciplinary)

The measurement of oxygen potential was conducted at 1,673, 1,773, and 1,873 K for (U$$_{0.623}$$Pu$$_{0.350}$$Am$$_{0.027}$$)O$$_{2}$$ and at 1,873 and 1,923 K for (U$$_{0.553}$$Pu$$_{0.285}$$Am$$_{0.015}$$Np$$_{0.147}$$)O$$_{2}$$ by using a thermo-gravimeter and an oxygen sensor. Am inclusion in terms of substituting the U significantly increased the oxygen potential. Similarly, the inclusion of Np as a substitute for U increased the oxygen potential; however, the effect was not as large as that with the Pu or Am addition at the same rate. The results were analyzed via defect chemistry and certain defect formations were suggested in the reducing region and the near-stoichiometric region by plotting the relationship between PO$$_{2}$$ and the deviation from the stoichiometry. The equilibrium constants of the defect reactions were arranged to reproduce the experiment such that Am/Np contents were included in the entropy with coefficients fitting the experimental data.

Journal Articles

Voltage drop analysis and leakage suppression design for mineral-insulated cables

Hirota, Noriaki; Shibata, Hiroshi; Takeuchi, Tomoaki; Otsuka, Noriaki; Tsuchiya, Kunihiko

Journal of Nuclear Science and Technology, 57(12), p.1276 - 1286, 2020/12

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

The influence of materials of mineral-insulated (MI) cables on their electrical characteristics upon exposure to high-temperature conditions was examined via a transmission test, in the objective of achieving the stability of the potential distribution along the cable length. Occurrence of a voltage drop along the cable was confirmed for aluminum oxide (Al$$_{2}$$O$$_{3}$$) and magnesium oxide (MgO), as insulating materials of the MI cable. A finite-element method (FEM)-based analysis was performed to evaluate the leakage in the potentials, which was found at the terminal end. Voltage drop yields by the transmission test and the analysis were in good agreement for the MI cable of Al$$_{2}$$O$$_{3}$$ and MgO materials, which suggests the reproducibility of the magnitude relationship of the experimental results via the FEM analysis. To suppress the voltage drop, the same FEM analysis was conducted, the diameter of the core wires ($$d$$) and the distance between them ($$l$$) were varied. Considering the variation of $$d$$, the potential distribution in the MI cable produced a minimum voltage drop corresponding to a ratio $$d/D$$ of 0.35, obtained by dividing $$d$$ with that of the insulating material ($$D$$). In case of varying $$l$$, a minimum voltage drop was l/$$D$$ of 0.5.

Journal Articles

Preliminary verification of water radiolysis and ECP calculation models by in-pile ECP measurements

Hanawa, Satoshi; Hata, Kuniki; Chimi, Yasuhiro; Kasahara, Shigeki

Proceedings of 21st International Conference on Water Chemistry in Nuclear Reactor Systems (Internet), 12 Pages, 2019/09

Journal Articles

Thermal and mechanical properties of CeO$$_{2}$$

Suzuki, Kiichi; Kato, Masato; Sunaoshi, Takeo*; Uno, Hiroki*; Carvajal-Nunez, U.*; Nelson, A. T.*; McClellan, K. J.*

Journal of the American Ceramic Society, 102(4), p.1994 - 2008, 2019/04

The fundamental properties of CeO$$_{2}$$ were assessed using a range of experimental techniques. The oxygen potential of CeO$$_{2}$$ was measured by the thermogravimetric technique, and a numerical fit for the oxygen potential of CeO$$_{2}$$ is derived based on defect chemistry. Mechanical properties of CeO$$_{2}$$ were obtained using sound velocity measurement, resonant ultrasound spectroscopy and nanoindentation. The obtained mechanical properties of CeO$$_{2}$$ are then used to evaluate the Debye temperature and Gruneisen constant. The heat capacity and thermal conductivity of CeO$$_{2}$$ were also calculated using the Debye temperature and the Gruneisen constant. Finally, the thermal conductivity was calculated based upon laser flash analysis measurements. This result demonstrates that the thermal conductivity has strong dependence upon material purity.

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:2 Percentile:17.39(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

Seawater effects on the soundness of spent fuel cladding tube

Motooka, Takafumi; Ueno, Fumiyoshi; Yamamoto, Masahiro

Proceedings of 2016 EFCOG Nuclear & Facility Safety Workshop (Internet), 6 Pages, 2016/09

At the Fukushima Daiichi nuclear accident, seawater was injected into spent fuel pools of Unit 2-4 for the emergency cooling. Seawater might cause localized corrosion of spent fuel cladding. This would lead to leakage of not only fissile materials but also fission products from fuel cladding. The behavior, however, is not understood well. In this paper, the effects of seawater on corrosion behavior and mechanical property of were studied by using a spent fuel cladding from a BWR. We immersed the spent cladding tubes in diluted artificial seawater for 300h at 353 K, and conducted their visual, cross-sectional and strength examinations. As a localized corrosion index, the pitting potentials of specimens fabricated from the cladding were measured as functions of chloride ion concentration ranging from 20 to 2500 ppm. The visual examination showed that localized corrosion has not occurred, and cross-sectional examination showed no cracks. The strength of immersed tubes was comparable to that of non-immersed tubes. Additionally, pitting potential could not be measured over 1.0 V; pitting corrosion was hardly occurred. These results suggested that the specimens from the spent fuel cladding tube was very resistant to localized corrosion.

Journal Articles

Effects of gamma-ray irradiation on spontaneous potential of stainless steel in zeolite-containing diluted artificial seawater

Kato, Chiaki; Sato, Tomonori; Ueno, Fumiyoshi; Yamagishi, Isao

Proceedings of 17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Vol.2, p.1357 - 1374, 2016/05

With respect to the long-term storage of the zeolite-containing spent Cs adsorption vessels used at the Fukushima Daiichi Nuclear Power Station, the corrosion of the vessel material is one of the most important issues. In this study, we performed electrochemical tests on stainless steel specimens in zeolite-containing artificial seawater under gamma-ray irradiation. The spontaneous potential ESP and critical pitting potential VC of the type 316L steel in systems in contact with various zeolites were measured in order to evaluate the corrosion resistance of the steel. In addition, the water sample was analyzed after being irradiated, in order to determine the concentrations of various dissolved oxidants such as oxygen and hydrogen peroxide, which can accelerate the corrosion process. The steady-state rest potential increased with an increase in the dose rate; however, the increase was suppressed in contact with the zeolites. The VC value of the steel when in contact with the zeolites was slightly smaller than the VC value in bulk water; however, the choice of the zeolite used as herschelite, IE96 and IE911 hardly affect the VC value. The concentration of H$$_{2}$$O$$_{2}$$ in the bulk water under irradiation also increased with the increase in the dose rate. This increase was suppressed in the systems in contact with the zeolites, owing to the decomposition of the H$$_{2}$$O$$_{2}$$ by the zeolites. A clear relationship was observed between ESP and the H$$_{2}$$O$$_{2}$$ concentration. As contact with the zeolites caused the increase in ESP under irradiation to be suppressed, it can be concluded that the presence of zeolites in the spent Cs adsorption vessels can reduce the probability of the localized corrosion of the stainless steel in the vessels.

JAEA Reports

Study on innovative HTGR to reduce generation of potential radiotoxicity

Fukaya, Yuji; Goto, Minoru; Nishihara, Tetsuo

JAEA-Research 2015-023, 44 Pages, 2016/02

JAEA-Research-2015-023.pdf:2.13MB

A study on innovative High Temperature Gas-cooled Reactor (HTGR) to reduce generation of potential radiotoxicity had been performed. Unlike the Fast Breeder Reactor (FBR) and Accelerated Driven System (ADS), which can confine radioactive nuclides into its fuel cycle as multi-recycling and transmute, in this study we attempt to reduce the generation of the radiotoxicity itself by preventing the generation of Pu and MA, which is generated with the energy generation. In this context, we proposed the innovative HTGR that employs the Highly Enriched Uranium (HEU) fuel by removing $$^{238}$$U : source of the Pu and MA. However, there are the problems of fuel integrity, nuclear proliferation, nuclear self-regulation characteristics, and economy of electricity generation which are caused by employing HEU. For these problems, we investigated and proposed the solutions. Especially for the nuclear self-regulation characteristics, which were improved by adding Er, the optimized nuclear design was quantitatively determined and elucidated by the Bondarenko approach. As a result, it was confirmed that the proposed reactor can solves these problem for employing HEU fuel and the high specification and economy as same as those of standard HTGR fueled uranium.

Journal Articles

Corrosion of structural materials and electrochemistry in high-temperature water; Relationships among water chemistry, corrosion, oxide film and electrochemical corrosion potential

Uchida, Shunsuke; Hanawa, Satoshi; Kysela, J.*; Lister, D. H.*

Power Plant Chemistry, 18(1), p.6 - 17, 2016/01

In order to establish reliable NPP operation, each plant requires its own unique optimal water chemistry control based on careful consideration of its system, materials and operational history. Electrochemistry is one of key issues that determine corrosion related problems, e.g., FAC. Based on the relationships among ECP, metal surface conditions and exposure time, a model to evaluate ECP and corrosion rate of steel was developed by coupling an electrochemical model and an oxide layer growth model. Major conclusions are as follows. (1) The effects of water chemistry improvement and mass transfer coefficients due to local flow velocity on FAC wall thinning rate and ECP could be evaluated with the proposed model. (2) The effects of H$$_{2}$$O$$_{2}$$ and O$$_{2}$$ concentrations on ECP were evaluated with the model. Exposure time dependent ECPs were also explained as the effects of oxide film growth on the specimens. (3) Decreases in ECP due to neutron exposure were explained by radiation-induced diffusion in the oxide layers.

Journal Articles

Corrosion of the stainless steel in the zeolite containing diluted artificial seawater under $$gamma$$-ray irradiation

Kato, Chiaki; Sato, Tomonori; Nakano, Junichi; Ueno, Fumiyoshi; Yamagishi, Isao

Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10

As a part of consideration for long-term storage of spent zeolite adsorption vessels in the Fukushima Daiichi Nuclear Power Station, corrosion of vessel material in the spent zeolite adsorption vessel is one of important issue. We performed electrochemical tests of stainless steel (type 316L) in the zeolite containing artificial seawater under $$gamma$$-ray irradiation. Steady spontaneous potential (Esp) and pitting potential (VC), of type 316L was measurement. $$^{60}$$Co $$gamma$$-rays source was used under irradiation. Dose rate of $$gamma$$-ray irradiation was controlled for 5 kGy/h and 400 Gy/h. In anode polarization curves, there was no clear difference under irradiation and non-irradiation. The corrosion potential of type 316L increased with increasing time after $$gamma$$-ray irradiation. The Esp was shifted to nobler by $$gamma$$-rays irradiation, while increasing Esp was suppressed by contacted with zeolite.

Journal Articles

Thermodynamic evaluation on chemical reaction between degraded nuclear fuel and B$$_{4}$$C control rod in severe accident of LWR

Shirasu, Noriko; Kurata, Masaki; Ogawa, Toru*

Proceedings of 2014 Water Reactor Fuel Performance Meeting/ Top Fuel / LWR Fuel Performance Meeting (WRFPM 2014) (USB Flash Drive), 6 Pages, 2014/09

In the accident of Fukushima-Daiichi Nuclear Power Plant, degraded fuels containing Zircaloy probably reacted with B$$_{4}$$C control blades containing stainless steel cladding or blade sheath. Since light elements like B and C are able to react easily with various elements and form various chemical species, several concerns are pointed out, such as variation in volatility and heat generation by oxidation of B and C. The chemical states of degraded fuel were evaluated on the assumption of thermodynamic equilibrium under various conditions of oxygen potential and temperature. The chemical behavior of B affects significantly the variation in oxygen potential with progressing severe accident, and many kinds of volatile compounds are formed by oxidation. The behavior of B causes the changes of volatility of FPs, such as Sr, Cs and Mo.

Journal Articles

Determination of uranium and rare-earth metals separation coefficients in LiCl-KCl melt by electrochemical transient techniques

Kuznetsov, S. A.*; Hayashi, Hirokazu; Minato, Kazuo; Gaune-Escard, M.*

Journal of Nuclear Materials, 344(1-3), p.169 - 172, 2005/09

 Times Cited Count:24 Percentile:84.12(Materials Science, Multidisciplinary)

The knowledge of separation coefficients of actinides and rare-earth metals is important for developing pyrometallurgical process of spent nuclear fuel. Electrochemical experiments were carried out at 723-823 K to estimate separation coefficients in LiCl-KCl eutectic melt containing uranium and lanthanum trichlorides. Uranium and lanthanum separation coefficients is calcurated with the voltammetric peak potentials of U (III) and La (III), their concentration in the melt and kinetic parameters for U(III) discharge such as diffusion coefficients, and standard rate constants of charge transfer. The diffusion coefficients of U (III) were determined by some electrochemical measurements. The standard rate constants of charge transfer for electroreduction of uranium U(III) +3e$$^{-}$$ =U were calculated by impedance spectroscopy method.

Journal Articles

Observation of nonlinear coupling between small-poloidal wave-number potential fluctuations and turbulent potential fluctuations in Ohmically heated plasmas in the JFT-2M tokamak

Nagashima, Yoshihiko*; Hoshino, Katsumichi; Ejiri, Akira*; Shinohara, Koji; Takase, Yuichi*; Tsuzuki, Kazuhiro; Uehara, Kazuya; Kawashima, Hisato; Ogawa, Hiroaki; Ido, Takeshi*; et al.

Physical Review Letters, 95(9), p.095002_1 - 095002_4, 2005/08

 Times Cited Count:97 Percentile:92.95(Physics, Multidisciplinary)

By a reciprocating electrostatic probe, two types of low frequency coherent electrostatic modes (about1kHz and 10-15kHz) are found,for the first time, in the edge region of ohmically heated plasmas in the JFT-2M tokamak. These modes exists in the last closed surface. The higher frequency mode has features of the geodesic acoustic mode (GAM), though the low frequency mode is not identified yet. A bispectral analysis revealed that significant nonlinear couplings (parametric modulation) between these coherent fluctuations and broadband background turbulent potential fluctuations occur. In the other words, the GAM and the back ground turbulence are modulated by the newly found low frequency electrostatic mode (further, the GAM modulates the background turbulence, also) for the first time. The newly found low frequency mode (frequency about 1kHz) is supposed to contribute to the turbulent diffusion nonlinearly.

Journal Articles

A Modified version of the analytical potential function for the global ab initio ground-state potential energy surface of the BrH$$_{2}$$ system

Kurosaki, Yuzuru; Takayanagi, Toshiyuki*

Chemical Physics Letters, 406(1-3), p.121 - 125, 2005/04

no abstracts in English

Journal Articles

Electrochemical behavior and some thermodynamic properties of UCl$$_4$$ and UCl$$_3$$ dissolved in a LiCl-KCl eutectic melt

Kuznetsov, S. A.*; Hayashi, Hirokazu; Minato, Kazuo; Gaune-Escard, M.*

Journal of the Electrochemical Society, 152(4), p.C203 - C212, 2005/04

 Times Cited Count:87 Percentile:93.34(Electrochemistry)

The electrochemical behavior of UCl$$_4$$ and UCl$$_3$$ dissolved in LiCl-KCl eutectic melt was studied at 723-823 K. Electroreduction of U(IV) in LiCl-KCl melt occurs via two successive steps involving transfer of one and three electrons. The diffusion coefficients of U(IV) and U(III) ions were determined by linear sweep voltammetry, chronopotentiometry, and chronoamperometry. The formal standard potential of E$$^*$$U(IV)/U(III), E$$^*$$U(IV)/U, and E$$^*$$U(III)/U were determined and some thermodynamic properties of UCl$$_4$$ and UCl$$_3$$ dissolved in LiCl-KCl eutectic melt were calculated. Influence of oxide ions on electrochemical behavior was also studied.

Journal Articles

Parallel and radial transport of ELM plasma in the SOL and divertor of JT-60U

Asakura, Nobuyuki; Takechi, Manabu; Oyama, Naoyuki; Nakano, Tomohide

Journal of Nuclear Materials, 337-339, p.712 - 716, 2005/03

 Times Cited Count:14 Percentile:70.37(Materials Science, Multidisciplinary)

Fast sampling diagnostics such as Langmuir probes and magnetic pick-up coils were developed in JT-60U. ELM radial expansion was important to understand the heat and particle load on the first wall. Enhancement and radial expansion of the SOL plasma just after ELM were investigated at Low-Field-Side and High-Field-Side. Ion saturation current ($$j$$$$_{s}$$) profile was described by two-exponential fit (i.e. 1st and 2nd lgi). Enhancement of the particle flux was different in poloidal location: particle flux profile became very flat, in particular, at HFS. Radial expansion speed at LFS was evaluated in the range of 1-3 km/s. ELM plasma flux in LFS and HFS divertors was investigated. Fast changes of js and floating potential (Vf) were measured. Large negative Vf was observed and durations of the negative js and Vf were $$sim$$100 ms, which was shorter than heat deposition ($$sim$$250 ms). The large negative js and Vf near both strike-points suggested fast electron deposition rather than thermal electric current. Influence of the divertor sheath on the heat deposition time is discussed.

Journal Articles

Oxygen potential and defect structure of oxygen-excess pyrochlore Ce$$_{2}$$Zr$$_{2}$$O$$_{7+x}$$

Otobe, Haruyoshi; Nakamura, Akio; Yamashita, Toshiyuki; Minato, Kazuo

Journal of Physics and Chemistry of Solids, 66(2-4), p.329 - 334, 2005/02

 Times Cited Count:22 Percentile:65.2(Chemistry, Multidisciplinary)

Pyrochlore-type (P-type) zirconias have been attracting significant research interest as disposable forms of high-level radioactive waste. In this work, we have clarified the oxygen potentials (g(O$$_{2}$$)) vs. oxygen nonstoichiometry (x) and temperature relations of P-type Ce$$_{2}$$Zr$$_{2}$$O$$_{7+x}$$ by the emf method and determined the lattice parameters (a0) with respect to x by XRD method.

Journal Articles

A Note on the basis set approach in the constrained interpolation profile method

Utsumi, Takayuki*; Yabe, Takashi*; Koga, J. K.; Aoki, Takayuki*; Sekine, Masatoshi*; Ogata, Yoichi*; Matsunaga, Eiichi*

Journal of Computational Physics, 196(1), p.1 - 7, 2004/05

 Times Cited Count:3 Percentile:21.31(Computer Science, Interdisciplinary Applications)

no abstracts in English

JAEA Reports

Bioinformatics; Construction of protein 3D structure prediction system

Kimura, Hideo; Sakai, Tomo*

JAERI-Data/Code 2004-008, 41 Pages, 2004/02

JAERI-Data-Code-2004-008.pdf:4.76MB

no abstracts in English

JAEA Reports

Evaluation of susceptibility on crevice corrosion for ITER vacuum vessel

Nakahira, Masataka

JAERI-Tech 2003-083, 79 Pages, 2003/11

JAERI-Tech-2003-083.pdf:10.29MB

The ITER Vacuum Vessel has a double-walled structure and cooling water is filled in between inner and outer shells. It is planned to apply T-welded joints with partial penetration at the connection between outer shell and rib. The length and gap of non-penetrated part are controlled and limited to less than 5mm and 0.5mm respectively. Although it can be considered to be low susceptibility, crevice corrosion can possibly occur, because the water is stagnant in the crevice and impurities will condense. In this report, the corrosion-crevice repassivation potential, E$$_{R,CREV}$$, was experimentally measured under the several density of NaCl solution, and compared to the steady-state corrosion potential in the pertinent environment, to evaluate the susceptibility. Simulated conditions are normal operating condition with water temperature of 150$$^{circ}$$C, baking operation with water temperature of 200$$^{circ}$$C and impurity condense by cyclic wet and dry condition.

103 (Records 1-20 displayed on this page)