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Journal Articles

Alloy design and characterization of a recrystallized FeCrAl-ODS cladding for accident-tolerant BWR fuels; An Overview of research activity in Japan

Ukai, Shigeharu; Sakamoto, Kan*; Otsuka, Satoshi; Yamashita, Shinichiro; Kimura, Akihiko*

Journal of Nuclear Materials, 583, p.154508_1 - 154508_24, 2023/09

 Times Cited Count:0 Percentile:78.15(Materials Science, Multidisciplinary)

Journal Articles

Formation of nanoscale protrusions on polymer films after atomic oxygen exposure; Observations with positron annihilation lifetime spectroscopy

Goto, Aki*; Michishio, Koji*; Oka, Toshitaka; Tagawa, Masahito*; Yamashita, Shinichi*

Langmuir, 39(34), p.11954 - 11963, 2023/08

Atomic oxygen (AO) is one of the dominant components of the residual atmosphere in low Earth orbit. AO collides with spacecraft with translational energy of 5 eV, forming nanoscale protrusions on polymeric materials. This study investigated the size of free-volume holes and the layer thickness that interacted with AO for polyethylene (PE), polypropylene (PP), and polystyrene (PS) by positron annihilation lifetime spectroscopy. By the AO irradiation, oxidized layer formed in the surface, and the maximum depth of the oxidized layer for PE and PP were deeper than for PS. The different sizes of free-volume holes would affect the injection depths of AO, resulting in the oxidized layers' thicknesses and surface morphologies.

Journal Articles

Development of a numerical simulation method for air cooling of fuel debris by JUPITER

Yamashita, Susumu; Uesawa, Shinichiro; Ono, Ayako; Yoshida, Hiroyuki

Mechanical Engineering Journal (Internet), 10(4), p.22-00485_1 - 22-00485_25, 2023/08

A detailed evaluation for air cooling of fuel debris in actual reactors will be essential in fuel debris retrieval under dry conditions. To understand the heat transfer in and around fuel debris, which is assumed as a porous medium in the primary containment vessel (PCV) mechanistically, we newly applied the porous medium model to the multiphase and multicomponent computational fluid dynamics code named JUPITER (JAEA Utility Program for Interdisciplinary Thermal-hydraulics Engineering and Research). We applied the Darcy-Brinkman model as for the porous medium model. This model has high compatibility with JUPITER because it can treat both a pure fluid and a porous medium phase simultaneously in the same manner as the one-fluid model in multiphase flow simulation. We addressed the case of natural convection with a high-velocity flow standing out nonlinear effects by implementing the Forchheimer model, including the term of the square of the velocity as a nonlinear effect to the momentum transport equation of JUPITER. We performed some simple verification and validation simulations, such as the natural convection simulation in a square cavity and the natural convective heat transfer experiment with the porous medium, to confirm the validity of the implemented model. We confirmed that the result of JUPITER agreed well with these simulations and experiments. In addition, as an application of the updated JUPITER, we performed the preliminary simulation of air cooling of fuel debris in the condition of the Fukushima Daiichi Nuclear Power Station unit 2 including the actual core materials. As a result, JUPITER calculated the temperature and velocity field stably in and around the fuel debris inside the PCV. Therefore, JUPITER has the potential to estimate the detailed and accurate thermal-hydraulics behaviors of fuel debris.

Journal Articles

Development of numerical simulation method of natural convection around heated porous medium by using JUPITER

Uesawa, Shinichiro; Yamashita, Susumu; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 9 Pages, 2023/05

For contaminated water management in decommissioning Fukushima Daiichi Nuclear Power Stations, reduction in water injection, intermittent injection water and air cooling are considered. However, since there are uncertainties of fuel debris in the PCV, it is necessary to examine and evaluate optimal cooling methods according to the distribution state of the fuel debris and the progress of the fuel debris retrieval work in advance. We have developed a method for estimating the thermal behavior in the air cooling, including the influence of the position, heat generation and the porosity of fuel debris. Since a large-scale thermal-hydraulics analysis of natural convection is necessary for the method, JUPITER developed independently by JAEA is used. It is however difficult to perform the large-scale thermal-hydraulics analysis with JUPITER by modeling the internal structure of the debris which may consist of a porous medium. Therefore, it is possible to analyze the heat transfer of the porous medium by adding porous models to JUPITER. In this study, we report the validation of JUPITER applied the porous model and discuss which heat transfer models are most effective in porous models such as series, parallel and geometric mean models. To obtain validation data of JUPITER for the natural convective heat transfer analysis around the porous medium, we performed the heat transfer and the flow visualization experiments of the natural convection in the experimental system including the porous medium. In the comparison between the experiment and the numerical analysis with each model, the numerical result with the geometric mean model was the closest of the models to the experimental results. However, the numerical results of the temperature and the velocity were overestimated for those experimental results. In particular, the temperature near the interface between the porous medium and air was more overestimated.

Journal Articles

Current status of accident tolerant fuel (ATF) development, 1; Overview of ATF development conducted under the technology development project for improving nuclear safety

Yamashita, Shinichiro

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 65(4), p.233 - 237, 2023/04

In the wake of the accident at the Fukushima Daiichi Nuclear Power Plant (NPP) of TEPCO due to the Great East Japan Earthquake in 2011, interest in the early implementation of accident tolerant fuel (ATF) not only for many existing NPPs but also for future NPPs, which is expected to dramatically improve the safety of light water reactors, has increased globally, and research and development is currently underway in many countries around the world. In this article, an overview of domestic ATF technology development that has been carried out with the support of the Ministry of Economy, Trade and Industry since 2015, will be introduced.

Journal Articles

A Numerical simulation method to evaluate heat transfer of fuel debris in air cooling by JUPITER, 1; Project overview and the applicability to the actual reactor system

Yamashita, Susumu; Uesawa, Shinichiro; Ono, Ayako; Yoshida, Hiroyuki

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 8 Pages, 2022/10

no abstracts in English

Journal Articles

A Numerical simulation method to evaluate heat transfer of fuel debris in air cooling by JUPITER, 2; Validation of porous model for natural convective heat transfer

Uesawa, Shinichiro; Yamashita, Susumu; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 8 Pages, 2022/10

Journal Articles

Atomic distribution and local structure in ice VII from in situ neutron diffraction

Yamashita, Keishiro*; Komatsu, Kazuki*; Klotz, S.*; Fabelo, O.*; Fern$'a$ndez-D$'i$az, M. T.*; Abe, Jun*; Machida, Shinichi*; Hattori, Takanori; Irifune, Tetsuo*; Shimmei, Toru*; et al.

Proceedings of the National Academy of Sciences of the United States of America, 119(40), p.e2208717119_1 - e2208717119_6, 2022/10

 Times Cited Count:1 Percentile:18.46(Multidisciplinary Sciences)

Here we present the first elucidation of the disordered structure of ice VII, the dominant high-pressure form of water, at 2.2 GPa and 298 K from both single-crystal and powder neutron diffraction techniques. We reveal the three-dimensional atomic distributions from the maximum entropy method and unexpectedly find a ring-like distribution of hydrogen in contrast to the commonly-accepted discrete sites. In addition, total scattering analysis at 274 K clarified the difference in the intermolecular structure from ice VIII, the ordered counterpart of ice VII, despite an identical molecular geometry. Our complementary structure analyses robustly demonstrate the unique disordered structure of ice VII. Furthermore, these noble findings are related to the proton dynamics which drastically vary with pressure, and will contribute to an understanding of the structural origin of anomalous physical properties of ice VII under pressures.

Journal Articles

Study on the mechanism of radiolytic degradation of an extractant for minor actinides separation

Toigawa, Tomohiro; Kumagai, Yuta; Yamashita, Shinichi*; Ban, Yasutoshi; Matsumura, Tatsuro

UTNL-R-0502 (Internet), 2 Pages, 2022/04

This report summarizes the results obtained in FY2020 at the Electron Linac Facility of the University of Tokyo. The radiolysis process of ${it N,N,N',N',N'',N''}$-hexaoctyl nitrilotriacetamide (HONTA), which is expected to be used as an extractant in a separation process for minor actinides, diluted in dodecane was investigated by pulse radiolysis experiments. The radical cation and the triplet-excited state of HONTA were observed in the nanosecond time region. The transition from the radical cation to the triplet excited state was slowed down by adding electron scavengers, and further, the reactivity of the triplet excited state was also suppressed.

Journal Articles

Dislocation-climbing bypass over dispersoids with different lattice misfit in creep deformation of FeCrAl oxide dispersion-strengthened alloys

Ukai, Shigeharu; Yamashita, Shinichiro

Journal of Materials Research and Technology, 16, p.891 - 898, 2022/01

 Times Cited Count:7 Percentile:89.58(Materials Science, Multidisciplinary)

The creep strain rate of FeCrAl oxide dispersion-strengthened alloys, as a promising accident-tolerant fuel (ATF) cladding of the light-water reactors, is accelerated in YAlO$$_{3}$$ dispersoids by two to three orders of magnitude compared with Y$$_{4}$$Zr$$_{3}$$O$$_{12}$$ dispersoid at 1273K and even occurs at an applied stress less than threshold stress for dislocation detachment. Two approaches were carried out to interpret new findings and to clarify their mechanism. By optimizing the relaxation of the dislocation line energy at the dispersoid interface, numerical analyses proved the accelerated dislocation-climbing in the YAlO$$_{3}$$ dispersoids. The other is a more atomistic approach. The climbing force on the dislocation induced by the stress field around the dispersoid was analyzed in terms of the Peach-Koehler relationship. The accelerated creep strain rate in YAlO$$_{3}$$ dispersoids is attributed to a larger climbing force induced by larger lattice misfit with less coherency in YAlO$$_{3}$$ dispersoid.

Journal Articles

Summary results of subsidy program for the "Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy and Thermal Behavior Estimation of Fuel Debris))"

Koyama, Shinichi; Nakagiri, Toshio; Osaka, Masahiko; Yoshida, Hiroyuki; Kurata, Masaki; Ikeuchi, Hirotomo; Maeda, Koji; Sasaki, Shinji; Onishi, Takashi; Takano, Masahide; et al.

Hairo, Osensui Taisaku jigyo jimukyoku Homu Peji (Internet), 144 Pages, 2021/08

JAEA performed the subsidy program for the "Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy and Thermal Behavior Estimation of Fuel Debris))" in 2020JFY. This presentation summarized briefly the results of the project, which will be available shortly on the website of Management Office for the Project of Decommissioning and Contaminated Water Management.

Journal Articles

Orientation dependence of yield strength in a new single crystal-like FeCrAl oxide dispersion strengthened alloy

Aghamiri, S. M. S.*; Sugawara, Naoya*; Ukai, Shigeharu; Ono, Naoko*; Sakamoto, Kan*; Yamashita, Shinichiro

Materials Characterization, 176, p.111043_1 - 111043_6, 2021/06

Advanced oxidation-resistant FeCrAl ODS alloys were developed via the control of composition-processing conditions for the accident tolerant fuel (ATF) cladding. For the first time, a single-crystal like recrystallized FeCrAl ODS alloy was achieved with a unique crystallographic texture of 110-plane and 211-direction and a high number density of fine nanoscale oxide particles. Evaluation of yield strengths at different temperatures showed higher values in transverse (T) direction than longitudinal (L) direction. The crystal orientation dependence of the yield strength up to 800$$^{circ}$$C was attributed to lower value of Schmid factor in transverse direction. Accordingly, the critical resolved shear stress of this practical class of advanced materials was calculated in various temperatures.

Journal Articles

Radiation-induced effects on the extraction properties of hexa-$$n$$-octylnitrilo-triacetamide (HONTA) complexes of americium and europium

Toigawa, Tomohiro; Peterman, D. R.*; Meeker, D. S.*; Grimes, T. S.*; Zalupski, P. R.*; Mezyk, S. P.*; Cook, A. R.*; Yamashita, Shinichi*; Kumagai, Yuta; Matsumura, Tatsuro; et al.

Physical Chemistry Chemical Physics, 23(2), p.1343 - 1351, 2021/01

 Times Cited Count:9 Percentile:75.71(Chemistry, Physical)

The candidate An(III)/Ln(III) separation ligand hexa-$$n$$-octylnitrilo-triacetamide (HONTA) was irradiated under envisioned SELECT (Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation) process conditions using a solvent test loop in conjunction with cobalt-60 gamma irradiation. We demonstrate that HONTA undergoes exponential decay with increasing gamma dose to produce a range of degradation products which have been identified and quantified by HPLC-ESI-MS/MS techniques. The combination of HONTA destruction and degradation product ingrowth, particularly dioctylamine, negatively impacts the extraction and back-extraction of both americium and europium ions. The loss of HONTA was attributed to its reaction with the solvent (${it n}$-dodecane) radical cation of ${it k}$(HONTA + R$$^{.+}$$) = (7.61 $$pm$$ 0.82) $$times$$ 10$$^{9}$$ M$$^{-1}$$ s$$^{-1}$$ obtained by pulse radiolysis techniques. However, when this ligand is bound to either americium or europium ions, the observed ${it n}$-dodecane radical cation kinetics increase by over an order of magnitude. This large reactivity increase to additional reaction pathways occurring upon metal-ion binding. Lastly nanosecond time-resolved measurements showed that both direct and indirect HONTA radiolysis yielded the short-lived ($$<$$100 ns) HONTA radical cation as well as a longer-lived ($$mu$$s) HONTA triplet excited state. These HONTA species are important precursors to the suite of HONTA degradation products observed.

Journal Articles

Study on the mechanism of radiolytic degradation of an extractant for minor actinides separation

Toigawa, Tomohiro; Murayama, Rin*; Kumagai, Yuta; Yamashita, Shinichi*; Suzuki, Hideya; Ban, Yasutoshi; Matsumura, Tatsuro

UTNL-R-0501, p.24 - 25, 2020/12

This report summarizes the results obtained in FY2019 at Electron Linac Facility of University of Tokyo. The radiolysis process of a diglycolamide extractant, which is expected to be used in the separation process of minor actinides (MA), in dodecane and octanol solutions was investigated by pulse radiolysis. As a result, it was suggested that by adding alcohol, the decomposition process of the diglycolamide extractant was different from the decomposition processes in the single solvent of dodecane considered that the decomposition occurred via a radical cation species of the extractant.

Journal Articles

Locally mesh-refined lattice Boltzmann method for fuel debris air cooling analysis on GPU supercomputer

Onodera, Naoyuki; Idomura, Yasuhiro; Uesawa, Shinichiro; Yamashita, Susumu; Yoshida, Hiroyuki

Mechanical Engineering Journal (Internet), 7(3), p.19-00531_1 - 19-00531_10, 2020/06

A dry method is one of practical methods for decommissioning the TEPCO's Fukushima Daiichi Nuclear Power Station. Japan Atomic Energy Agency (JAEA) has been evaluating the air cooling performance of the fuel debris by using the JUPITER code based on an incompressible fluid model and the CityLBM code based on the lattice Boltzmann method (LBM). However, these codes were based on a uniform Cartesian grid system, and required large computational time and cost to capture complicated debris structures. We develop an adaptive mesh refinement (AMR) version of the CityLBM code on GPU based supercomputers and apply it to thermal-hydrodynamics problems. The proposed method is validated against free convective heat transfer experiments at JAEA. It is also shown that the AMR based CityLBM code on 4 NVIDIA TESLA V100GPUs gives 6.7x speedup of the time to solution compared with the JUPITER code on 36 Intel Xeon E5-2680v3 CPUs.

Journal Articles

Developments of nano-polycrystalline diamond anvil cells for neutron diffraction experiments

Komatsu, Kazuki*; Klotz, S.*; Nakano, Satoshi*; Machida, Shinichi*; Hattori, Takanori; Sano, Asami; Yamashita, Keishiro*; Irifune, Tetsuo*

High Pressure Research, 40(1), p.184 - 193, 2020/02

 Times Cited Count:11 Percentile:73.28(Physics, Multidisciplinary)

A new high pressure cells for neutron diffraction experiments using nano-polycrystalline anvil is presented. The cell design, off-line pressure generation tests and a gas-loading procedure for this cell are described. The performance is illustrated by powder neutron diffraction patterns of ice VII to $$sim$$ 82 GPa. We also demonstrate the feasibility of single crystal neutron diffraction experiments of Fe$$_{3}$$O$$_{4}$$ at ambient conditions using this cell and discuss the current limitation and future developments.

Journal Articles

Ice I$$_{rm c}$$ without stacking disorder by evacuating hydrogen from hydrogen hydrate

Komatsu, Kazuki*; Machida, Shinichi*; Noritake, Fumiya*; Hattori, Takanori; Sano, Asami; Yamane, Ryo*; Yamashita, Keishiro*; Kagi, Hiroyuki*

Nature Communications (Internet), 11, p.464_1 - 464_5, 2020/02

 Times Cited Count:40 Percentile:87.73(Multidisciplinary Sciences)

Water freezes below 0$$^{circ}$$C at ambient pressure ordinarily to ice I$$_{rm h}$$, with hexagonal stacking sequence. Under certain conditions, ice with a cubic stacking sequence can also be formed, but ideal ice I$$_{rm c}$$ without stacking-disorder has never been formed until recently. Here we demonstrate a route to obtain ice I$$_{rm c}$$ without stacking-disorder by degassing hydrogen from the high-pressure form of hydrogen hydrate, C$$_{2}$$, which has a host framework isostructural with ice I$$_{rm c}$$. The stacking-disorder free ice I$$_{rm c}$$ is formed from C$$_{2}$$ via an intermediate amorphous or nano-crystalline form under decompression, unlike the direct transformations occurring in ice XVI from neon hydrate, or ice XVII from hydrogen hydrate. The obtained ice I$$_{rm c}$$ shows remarkable thermal stability, until the phase transition to ice I$$_{rm h}$$ at 250 K, originating from the lack of dislocations. This discovery of ideal ice I$$_{rm c}$$ will promote understanding of the role of stacking-disorder on the physical properties of ice as a counter end-member of ice I$$_{rm h}$$.

Journal Articles

Microstructure and texture evolution and ring-tensile properties of recrystallized FeCrAl ODS cladding tubes

Aghamiri, S. M. S.*; Sowa, Takashi*; Ukai, Shigeharu*; Ono, Naoko*; Sakamoto, Kan*; Yamashita, Shinichiro

Materials Science & Engineering A, 771, p.138636_1 - 138636_12, 2020/01

 Times Cited Count:25 Percentile:89.71(Nanoscience & Nanotechnology)

Oxide dispersion strengthened (ODS) FeCrAl ferritic steels are being developed as potential accident tolerance fuel cladding materials for the light water reactors (LWRs) due to significant improvement in steam oxidation by alumina forming scale and good mechanical properties up to high temperatures. In this study, the microstructural characteristics and tensile properties of the two FeCrAl ODS cladding tubes with different extrusion temperatures of 1100$$^{circ}$$C and 1150$$^{circ}$$C were investigated during processing conditions. While the hot extruded sample showed micron sized elongated grains with strong $$alpha$$-fiber in $$<$$110$$>$$ texture, cold pilger rolling process change the microstructure to submicron/micron size grain structure along with texture evolution to both $$alpha$$-fiber ($$<$$110$$>$$ texture) and $$gamma$$-fiber ({111} texture) via crystalline rotations. Subsequently, final annealing resulted in evolution of microstructure to large grain recrystallized structure starting at recrystallization temperature of $$sim$$810-850$$^{circ}$$C. Two distinct texture development happened in recrystallized cladding tubes, i.e., only large elongated grains of (110) $$<$$211$$>$$ texture following extrusion temperature of 1100$$^{circ}$$C; and two texture components of (110) $$<$$211$$>$$ and {111} $$<$$112$$>$$ following higher extrusion temperature of 1150$$^{circ}$$C. The different texture development and retarding of recrystallization progress in 1100$$^{circ}$$C-extruded cladding tubes were attributed to higher distribution of oxide particles.

Journal Articles

Crystal structure of a high-pressure phase of magnesium chloride hexahydrate determined by ${it in-situ}$ X-ray and neutron diffraction methods

Yamashita, Keishiro*; Komatsu, Kazuki*; Hattori, Takanori; Machida, Shinichi*; Kagi, Hiroyuki*

Acta Crystallographica Section C; Structural Chemistry (Internet), 75(12), p.1605 - 1612, 2019/12

 Times Cited Count:6 Percentile:56.18(Chemistry, Multidisciplinary)

A crystal structure of a high-pressure phase of magnesium chloride hexahydrate (MgCl$$_{2}$$ $$cdot$$ 6H$$_{2}$$O-II) and its deuterated counterpart (MgCl$$_{2}$$ $$cdot$$ 6D$$_{2}$$O-II) have been identified for the first time by in-situ single-crystal X-ray and powder neutron diffraction. The crystal structure was analyzed by the Rietveld method for the neutron diffraction pattern based on the initial structure determined by single-crystal X-ray diffraction. This high-pressure phase has a similar framework to that in the known ambient-pressure phase, but exhibits some structural changes with symmetry reduction caused by a subtle modification in the hydrogen-bond network around the Mg(H$$_{2}$$O)$$_{6}$$ octahedra. These structural features reflect the strain in the high-pressure phases of MgCl$$_{2}$$ hydrates.

Journal Articles

Oxidation of silicon carbide in steam studied by laser heating

Pham, V. H.; Nagae, Yuji; Kurata, Masaki; Furumoto, Kenichiro*; Sato, Hisaki*; Ishibashi, Ryo*; Yamashita, Shinichiro

Proceedings of International Nuclear Fuel Cycle Conference / Light Water Reactor Fuel Performance Conference (Global/Top Fuel 2019) (USB Flash Drive), p.670 - 674, 2019/09

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