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

https://doi.org/10.1021/acs.langmuir.3c00224

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.

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.

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

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

Yamashita, Keishiro*; Komatsu, Kazuki*; Klotz, S.*; Fabelo, O.*; Fernndez-Daz, 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

https://doi.org/10.1073/pnas.2208717119

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.

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

https://doi.org/10.1016/j.jmrt.2021.11.123

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 dispersoids by two to three orders of magnitude compared with YZrO 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 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 dispersoids is attributed to a larger climbing force induced by larger lattice misfit with less coherency in YAlO dispersoid.

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

https://doi.org/10.1016/j.matchar.2021.111043

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 800C 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.

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.

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

https://doi.org/10.1080/08957959.2020.1727465

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 82 GPa. We also demonstrate the feasibility of single crystal neutron diffraction experiments of FeO at ambient conditions using this cell and discuss the current limitation and future developments.

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

https://doi.org/10.1016/j.msea.2019.138636

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 1100C and 1150C were investigated during processing conditions. While the hot extruded sample showed micron sized elongated grains with strong -fiber in 110 texture, cold pilger rolling process change the microstructure to submicron/micron size grain structure along with texture evolution to both -fiber (110 texture) and -fiber ({111} texture) via crystalline rotations. Subsequently, final annealing resulted in evolution of microstructure to large grain recrystallized structure starting at recrystallization temperature of 810-850C. Two distinct texture development happened in recrystallized cladding tubes, i.e., only large elongated grains of (110) 211 texture following extrusion temperature of 1100C; and two texture components of (110) 211 and {111} 112 following higher extrusion temperature of 1150C. The different texture development and retarding of recrystallization progress in 1100C-extruded cladding tubes were attributed to higher distribution of oxide particles.

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