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Journal Articles

Cathodoluminescence of cerium dioxide; Combined effects of the electron beam energy and sample temperature

Constantini, J.-M.*; Seo, P.*; Yasuda, Kazuhiro*; Bhuian, AKM S. I.*; Ogawa, Tatsuhiko; Gourier, D.*

Journal of Luminescence, 226, p.117379_1 - 117379_10, 2020/10

 Times Cited Count:1 Percentile:45.34(Optics)

Cathodo-luminescence is used for detection of lattice defects, in particular oxygen vacancies in ceramics induced by electrons. However, how oxygen vacancy production efficiency depends on sample temperature, incoming electron flux, and electron energy was not clear. In this study, oxygen vacancies were made in the specimens of CeO$$_{2}$$ by irradiation of 400-1250 keV electrons and the cathodoluminescence from thus induced vacancies were observed by photo-fiber probe combined with CCD. As the result, the dependence of luminescence intensity on specimen temperature depends on the carrier trapping frequency and luminescence efficiency while luminescence center production/annihilation speed determines the dependency on the incoming electron flux. Moreover, radiation transport calculation conducted by the particle transport simulation code PHITS indicates that the number of electrons above the defect production threshold energy is vital to explain incoming electron energy dependence.

Journal Articles

Local structure investigations of accumulated damage in irradiated MgAl$$_{2}$$O$$_{4}$$

Yoshioka, Satoru*; Tsuruta, Konosuke*; Yamamoto, Tomokazu*; Yasuda, Kazuhiro*; Matsumura, Sho*; Sugiyama, Takeharu*; Oba, Yojiro; Ishikawa, Norito; Kobayashi, Eiichi*; Okudaira, Koji*

Journal of the American Ceramic Society, 103(8), p.4654 - 4663, 2020/08

 Times Cited Count:1 Percentile:100(Materials Science, Ceramics)

X-ray absorption near edge structure (XANES) and small-angle X-ray scattering (SAXS) reveal the damaged structures in MgAl$$_{2}$$O$$_{4}$$ spinel induced by swift heavy ions. SAXS indicates the formation of ion tracks with cylindrical shape with a diameter of 5 nm. XANES indicates the cationic disordering between tetrahedral and octahedral sites by the irradiation. Quantitative analysis of XANES also reveals that cations preferably occupy the octahedral sites at high fluence.

Journal Articles

Production of $$^{266}$$Bh in the $$^{248}$$Cm($$^{23}$$Na,5$$n$$)$$^{266}$$Bh reaction and its decay properties

Haba, Hiromitsu*; Fan, F.*; Kaji, Daiya*; Kasamatsu, Yoshitaka*; Kikunaga, Hidetoshi*; Komori, Yukiko*; Kondo, Narumi*; Kudo, Hisaaki*; Morimoto, Koji*; Morita, Kosuke*; et al.

Physical Review C, 102(2), p.024625_1 - 024625_12, 2020/08

 Times Cited Count:0 Percentile:100(Physics, Nuclear)

Journal Articles

Strong flux pinning by columnar defects with directionally dependent morphologies in GdBCO-coated conductors irradiated with 80 MeV Xe ions

Sueyoshi, Tetsuro*; Kotaki, Tetsuya*; Furuki, Yuichi*; Fujiyoshi, Takanori*; Semboshi, Satoshi*; Ozaki, Toshinori*; Sakane, Hitoshi*; Kudo, Masaki*; Yasuda, Kazuhiro*; Ishikawa, Norito

Japanese Journal of Applied Physics, 59(2), p.023001_1 - 023001_7, 2020/02

 Times Cited Count:1 Percentile:52.74(Physics, Applied)

We show that Xe ion irradiation with 80 MeV to GdBa$$_{2}$$Cu$$_{3}$$Oy-coated conductors creates different morphologies of columnar defects (CDs) depending on the irradiation angles relative to the c-axis: continuous CDs with a larger diameter are formed for oblique irradiation at $$theta_{rm i}$$ = 45$$^{circ}$$, whereas the same ion beam at a different angle ($$theta_{rm i}$$ = 0$$^{circ}$$) induces the formation of discontinuous CDs. The direction-dependent morphologies of CDs significantly affect the angular behavior of the critical current density $$J_{rm c}$$.

Journal Articles

Cathodoluminescence induced in oxides by high-energy electrons; Effects of beam flux, electron energy, and temperature

Constantini, J.-M.*; Ogawa, Tatsuhiko; Bhuian, A. S. I.*; Yasuda, Kazuhiro*

Journal of Luminescence, 208, p.108 - 118, 2019/04

 Times Cited Count:1 Percentile:77.51(Optics)

Cathodo-luminescence is used for detection of lattice defects, in particular oxygen vacancies in ceramics induced by electrons. However, how oxygen vacancy production efficiency depends on sample temperature, incoming electron flux, and electron energy was not clear. In this study, oxygen vacancies were made in the specimens of Al$$_{2}$$O$$_{3}$$, ZrO$$_{2}$$:Y(Yttrium stabilized zirconia), MgAl$$_{2}$$O$$_{4}$$, and TiO$$_{2}$$ by irradiation of 400-1250keV electrons and the cathodoluminescence from thus induced vacancies were observed by photo-fiber probe combined with CCD. As the result, the dependence of luminescence intensity on specimen temperature depends on the carrier trapping frequency and luminescence efficiency while luminescence center production/annihilation speed determines the dependency on the incoming electron flux. Moreover, radiation transport calculation conducted by the particle transport simulation code PHITS indicates that the number of electrons above the defect production threshold energy is vital to explain incoming electron energy dependence.

Journal Articles

X-ray absorption near edge structure and first-principles spectral investigations of cationic disorder in MgAl$$_{2}$$O$$_{4}$$ induced by swift heavy ions

Yoshioka, Satoru*; Tsuruta, Konosuke*; Yamamoto, Tomokazu*; Yasuda, Kazuhiro*; Matsumura, Sho*; Ishikawa, Norito; Kobayashi, Eiichi*

Physical Chemistry Chemical Physics, 20(7), p.4962 - 4969, 2018/02

 Times Cited Count:3 Percentile:83(Chemistry, Physical)

Cationic disorder in the MgAl$$_{2}$$O$$_{4}$$ spinel induced by swift heavy ions was investigated using the X-ray absorption near edge structure. With changes in the irradiation fluences of 200 MeV Xe ions, the Mg K-edge and Al K-edge spectra were synchronously changed. The calculated spectra based on density function theory indicate that the change in the experimental spectra was due to cationic disorder between Mg in tetrahedral sites and Al in octahedral sites. These results suggest a high inversion degree to an extent that the completely random configuration is achieved in MgAl$$_{2}$$O$$_{4}$$ induced by the high density electronic excitation under swift heavy ion irradiation.

Journal Articles

Influence of discontinuous columnar defects on flux pinning properties in GdBCO coated conductors

Sueyoshi, Tetsuro*; Kotaki, Tetsuya*; Furuki, Yuichi*; Uraguchi, Yusei*; Kai, Takashi*; Fujiyoshi, Takanori*; Shimada, Yusuke*; Yasuda, Kazuhiro*; Ishikawa, Norito

IEEE Transactions on Applied Superconductivity, 25(3), p.6603004_1 - 6603004_4, 2015/06

 Times Cited Count:6 Percentile:58(Engineering, Electrical & Electronic)

To investigate the effect of discontinuity of 1-D pinning centers on the flux pinning in a wide range of magnetic field directions, discontinuous columnar defects (CDs) and continuous CDs were formed in GdBCO coated conductors using Xe-ion irradiations with 80 and 270 MeV, respectively. An overall shift upward in Jc, for the 80-MeV-irradiated sample compared to the 270-MeV-irradiated one, can be observed in every direction of magnetic field, which is more remarkable as temperature decreases. This implies a synergetic effect of the pinning interaction between the linearity and the discontinuity for the discontinuous CDs.

Journal Articles

Atomic structure of ion tracks in Ceria

Takaki, Seiya*; Yasuda, Kazuhiro*; Yamamoto, Tomokazu*; Matsumura, Sho*; Ishikawa, Norito

Nuclear Instruments and Methods in Physics Research B, 326, p.140 - 144, 2014/05

 Times Cited Count:30 Percentile:4.16(Instruments & Instrumentation)

We have investigated atomic structure of ion tracks in CeO$$_{2}$$ irradiated with 200 MeV Xe ions by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). TEM observations under inclined conditions showed continuous ion tracks with diffraction and structure factor contrast, and the decrease in the atomic density of the ion tracks was evaluated. High resolution STEM with high-angle annular dark-field (HAADF) technique showed that the crystal structure of the Ce cation column is retained at the core region of ion tracks, although the signal intensity of the Ce cation lattice is reduced over a region nm in size. Annular bright field (ABF) STEM observation has detected that the O anion column is preferentially distorted at the core region of ion tracks within a diameter of 4 nm.

Journal Articles

Defect formation and accumulation in CeO$$_{2}$$ irradiated with swift heavy ions

Yasuda, Kazuhiro*; Eto, Motoki*; Sawada, Kenichi*; Yamamoto, Tomokazu*; Yasunaga, Kazufumi*; Matsumura, Sho*; Ishikawa, Norito

Nuclear Instruments and Methods in Physics Research B, 314, p.185 - 190, 2013/11

 Times Cited Count:24 Percentile:8.21(Instruments & Instrumentation)

We have investigated microstructure evolution in CeO$$_{2}$$ irradiated with 210 MeV Xe ions by using transmission electron microscopy to gain the fundamental knowledge on radiation damage induced by fission fragments in nuclear fuel and transmutation target.

Journal Articles

Accumulation of radiation damage and disordering in MgAl$$_{2}$$O$$_{4}$$ under swift heavy ion irradiation

Yasuda, Kazuhiro*; Yamamoto, Tomokazu*; Eto, Motoki*; Kawasoe, Shinji*; Matsumura, Sho*; Ishikawa, Norito

International Journal of Materials Research, 102(9), p.1082 - 1088, 2011/09

 Times Cited Count:9 Percentile:46.93(Metallurgy & Metallurgical Engineering)

Accumulation and recovery of radiation-induced damage with swift heavy ions instoichiometric magnesium aluminate spinel, MgAl$$_{2}$$O$$_{4}$$, has been investigated. Microstructural change and atomic disordering was examined through transmission electron microscopy (TEM) techniques, with bright-field (BF) and high-resolution (HR) TEM images, and high angular resolution electron channelling X-ray spectroscopy (HARECXS), for single crystal MgAl$$_{2}$$O$$_{4}$$ irradiated with 200 MeV Xe, and 340 or 350 MeV Au ions. The density of core damage region, detected by BFTEM with Fresnelcontrast, increased proportionally with ion fluence at the early stage of accumulation. This result is discussed with a balance between the formation and recovery of the core damage region under irradiation, and the influence region to induce the recovery was evaluated to be 7-9 nm in radius. The structure of the core damage region is found from HR and BFTEM images to be a columnar vacancy-rich region with a low atomic density.

Journal Articles

Development of high temperature gas-cooled reactor (HTGR) fuel in Japan

Ueta, Shohei; Aihara, Jun; Sawa, Kazuhiro; Yasuda, Atsushi*; Honda, Masaki*; Furihata, Noboru*

Progress in Nuclear Energy, 53(7), p.788 - 793, 2011/09

 Times Cited Count:20 Percentile:13.93(Nuclear Science & Technology)

In Japan, high temperature gas-cooled reactor (HTGR) fuel fabrication technologies have been developed by Nuclear Fuel Industries, Ltd. (NFI) with the collaboration of JAEA through the HTTR project since 1960's. NFI successfully fabricated first and second loading fuel (0.9 tU each) for the HTTR of JAEA. Its excellent quality was confirmed from the first loading fuel through the long-termed high temperature operation by the end of March 2010. Based on the HTTR fuel technologies, silicon carbide (SiC) coated fuel is being developed for burn-up extension. For an advanced fuel designs, replacement of the SiC layer by a zirconium carbide (ZrC) layer is a very promising example. JAEA has performed ZrC coating tests to investigate the influence of coating parameters and material properties such as stoichiometry and density of ZrC.

Journal Articles

Effect of heat treatment on TEM microstructures of Zirconium carbide coating layer in fuel particle for advanced high temperature gas cooled reactor

Aihara, Jun; Ueta, Shohei; Yasuda, Atsushi*; Takeuchi, Hitoshi*; Mozumi, Yasuhiro*; Sawa, Kazuhiro; Motohashi, Yoshinobu*

Materials Transactions, 50(11), p.2631 - 2636, 2009/11

 Times Cited Count:8 Percentile:50.26(Materials Science, Multidisciplinary)

The ZrC coating layer has been fabricated using the bromide process at JAEA. The coated particles with IPyC layers reported in a previous study were annealed at around 1800$$^{circ}$$C for 1h, under which compact sintering will be done in a practical process, in order to study effects of the heat treatment (annealing) on their microstructure evolution. Then the microstructures of the ZrC layers in the cases (batches) of C/Zr = 1.11 and 1.35 were characterized by means of TEM and STEM. Certain changes in the shape and size of voids or free carbons region caused by the heat treatment were found in the cases of both batches. After the heat treatment, the voids or free carbons region have shown a clod like feature with diameters of 50 to 100 nm. The grain growth of ZrC was also observed in both cases: In the ZrC layer with C/Zr = 1.11, the fibrous carbons grew as of to stand from the PyC to ZrC layers on some places in the IPyC/ZrC boundary.

JAEA Reports

Development of production technology of ZrC-coated particle, 2 (Contract research)

Yasuda, Atsushi; Ueta, Shohei; Aihara, Jun; Ishibashi, Hideharu*; Sawa, Kazuhiro

JAEA-Technology 2008-083, 11 Pages, 2009/01

JAEA-Technology-2008-083.pdf:3.14MB

The Very-High-Temperature Reactor (VHTR) is one of the candidates for the Generation IV nuclear energy system. ZrC coated fuel particles are expected to make the performance of the VHTR higher. Therefore, we are investigating the ZrC-coating process. From April 2007 to March 2008, ZrC-outer pyrolytic carbon (OPyC) layer continuous coating tests were carried out with the nonnuclear particles and we succeeded to coat continuously the ZrC layer and the OPyC layer with the thicknesses up to about 27 and about 48 $$mu$$m, respectively, in the batch scale of 100 g.

Journal Articles

TEM/STEM observation of ZrC coating layer for advanced high-temperature gas-cooled reactor fuel, Part II

Aihara, Jun; Ueta, Shohei; Yasuda, Atsushi; Ishibashi, Hideharu; Mozumi, Yasuhiro; Sawa, Kazuhiro; Motohashi, Yoshinobu*

Journal of the American Ceramic Society, 92(1), p.197 - 203, 2009/01

 Times Cited Count:7 Percentile:54.3(Materials Science, Ceramics)

The ZrC coating layer was fabricated with bromide process at JAEA. In a later stage of the project, we have successfully kept nominal deposition temperature almost constant. Microstructures of the ZrC layers, of which nominal deposition temperatures were able to measure, were characterized by means of TEM and STEM and the results were compared and discussed with those obtained for different batches including those reported in a previous study. The ZrC grains were oriented in the ZrC layers deposited at about 1630 K. This feature was rather different from that reported in the previous study. The formation of fairly different PyC structures was found on the PyC/ZrC boundary as well as around the pores existing near the boundary. Fibrous carbons were observed on the PyC/ZrC boundary produced in a batch deposited at a higher temperature (nominal temperature was 1769 K); no such fibrous carbons were found in a batch deposited at a lower temperature (nominal temperature was 1632 K).

JAEA Reports

Development of production technology of ZrC-coated particle, 1 (Contract research)

Yasuda, Atsushi; Ueta, Shohei; Aihara, Jun; Takeuchi, Hitoshi; Sawa, Kazuhiro

JAEA-Technology 2008-073, 18 Pages, 2008/11

JAEA-Technology-2008-073.pdf:3.81MB

As the conventional SiC-coated fuel particle, the ZrC-coated particle is proposed as a nuclear fuel for the Very High Temperature Reactor (VHTR) which is one of Generation IV nuclear reactors. Therefore it is examined by ZrC-coating equipment to get a ZrC-coating condition of C/Zr ratio 1.0, e.g., Zr and C atomic ratio equal to 1:1. Raw materials as surrogated kernel are Stabilized Zirconium Oxide (SZR) particle and PyC-coated SZR particle. For getting the basic production technology for mass production, the ZrC-coating parametric exanimation (coating gas flow rate, coating temperature and so on) is done up to 100 g as the equipment inventory. As the result of parameter examination, finally it could make the ZrC-coated particle with a thickness of ZrC layer of 0.030 mm and high quality in quantity of the particle inventory 100 g.

Journal Articles

Fabrication of uniform ZrC coating layer for the coated fuel particle of the very high temperature reactor

Ueta, Shohei; Aihara, Jun; Yasuda, Atsushi; Ishibashi, Hideharu; Takayama, Tomoo; Sawa, Kazuhiro

Journal of Nuclear Materials, 376(2), p.146 - 151, 2008/05

 Times Cited Count:47 Percentile:4.58(Materials Science, Multidisciplinary)

The Very-High-Temperature Reactor (VHTR) is the one of the most promising candidates for the Generation IV Nuclear Energy System. The VHTR fuel should exhibit excellent safety performance up to burn-ups of about 15 to 20%FIMA and fluences of 6$$times$$10$$^{25}$$ n/m$$^{2}$$(E$$>$$0.1 MeV). There is no experimental data which has proved the intactness of conventional SiC-coated fuel particles under such severe condition. Japan Atomic Energy Agency (JAEA) developed Zirconium carbide (ZrC)-coated fuel particles which is expected to maintain its intactness under higher temperature and burn-up compared with SiC-coating layer. JAEA has newly started the development of coating process by large-scale and of inspection method, and the irradiation of ZrC-coated particles from 2004. The fabrication tests of ZrC-coating have been started by new-series coater, and uniform ZrC coating layer has successfully been fabricated by the improvement of temperature control technique.

Journal Articles

Development on fabrication and inspection techniques for the ZrC-coated fuel particle as an advanced high temperature gas cooled reactor fuel

Ueta, Shohei; Aihara, Jun; Yasuda, Atsushi; Ishibashi, Hideharu; Mozumi, Yasuhiro; Sawa, Kazuhiro; Minato, Kazuo

Hyomen, 46(4), p.222 - 232, 2008/04

Japan Atomic Energy Agency (JAEA) is developing the zirconium carbide (ZrC) coated fuel particle which has better refractoriness and chemical stability than the conventional silicon carbide (SiC) coated fuel particle. In the present study, ZrC coating tests were carried out by the enlarged 200 g-scale ZrC coater comparing with the previous study. Finally, the stoichiometric ZrC layer was successfully fabricated by obtaining relationships between properties of ZrC, coating temperature and batch size through coating tests. In addition, not only inspection methods for coating thickness and density, but also treatment technique to remove pyrocarbon (PyC) layer were developed in order to evaluate the quality of the ZrC coated fuel particle. Present R&D will contribute to the practicability of the ZrC coated fuel particle as a fuel for the advanced high temperature gas cooled reactor such as the Very High Temperature Reactor (VHTR).

Journal Articles

TEM/STEM observation of ZrC-coating layer for advanced high-temperature gas-cooled reactor fuel

Aihara, Jun; Ueta, Shohei; Yasuda, Atsushi; Ishibashi, Hideharu; Takayama, Tomoo; Sawa, Kazuhiro; Motohashi, Yoshinobu*

Journal of the American Ceramic Society, 90(12), p.3968 - 3972, 2007/12

Japan Atomic Energy Agency (JAEA) has started to study and develop ZrC coated fuel particles for advanced high temperature gas cooled reactors. This paper mainly focuses on the microstructures of the ZrC and isotropic dense pyrolytic carbon (PyC) coating layer produced in the early stage of the project. The structure of free carbon region in the ZrC coating layer appears to be such that c-plane was along with the ZrC grain boundary. It appears that the existence of the free carbon phase, especially with such structure, deteriorates the fission product (FP) retention performance in addition to the mechanical strength of ZrC. The PyC coating layer appears to be a medium-range ordered amorphous structure.

JAEA Reports

Investigation on inspection methods for ZrC-coated fuel particle; Applicability evaluation of inspection methods for SiC-coated fuel particle

Takayama, Tomoo*; Ueta, Shohei; Aihara, Jun; Yasuda, Atsushi*; Ishibashi, Hideharu*; Sawa, Kazuhiro

JAEA-Research 2007-061, 32 Pages, 2007/09

JAEA-Research-2007-061.pdf:15.93MB

As the conventional SiC coated fuel particle, the ZrC coated fuel particle is proposed as a fuel for the Very High Temperature Gas-cooled Reactor (VHTR) which is one of Generation IV nuclear reactors. Applicability of inspection methods of SiC-coated fuel particle for ZrC-coated fuel particle has been examined by comparing properties of ZrC with SiC. It was suggested that hardness, absorption X-ray coefficient, density, oxidation-resistant and chemical stability of SiC were dominant properties for conventional inspection methods such as SiC coating layer thicknesses, coating layers densities for both SiC and O-PyC layers, thorough-coatings failure fraction and SiC coating layer failure fraction. With regards to the applicability of the inspection for the SiC-coated particle, some difficulties are revealed on coating layers densities for both ZrC and O-PyC layers and of ZrC failure fraction, and it was suggested that they were major issues to be solved.

Journal Articles

Study of irradiation induced restructuring of high burnup fuel; The New cross-over project (NXO) to study rim-structure formation

Kinoshita, Motoyasu*; Geng, H. Y.*; Chen, Y.*; Kaneta, Yasunori*; Iwasawa, Misako*; Onuma, Toshiharu*; Sonoda, Takeshi*; Yasunaga, Kazufumi*; Matsumura, Sho*; Yasuda, Kazuhiro*; et al.

Proceedings of 2006 International Meeting on LWR Fuel Performance (TopFuel 2006) (CD-ROM), p.248 - 254, 2006/10

The New Crossover Project (NXO) is studying effect of fission irradiation on fuel material that research activity is crossing over universities, national and private laboratories. Simulation studies are being performed to find principal and triggering processes of the rim-structure formation in high burnup LWR fuel pellet, using accelerator irradiation and computational calculations. Accelerator irradiation, high energy electron irradiation, fission energy particle beam and ion implantation (ragegas atoms) and combined overlapping irradiations are being performed. For the target of irradiation, CeO$$_{2}$$ isused as simulation of nuclear fuel. The initial results were such as planar structure made by Oxygen defects created by high energy electrons, and surface modification similar to grain-sub-division created by high fluence high energy particle irradiations.

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