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Journal Articles

Combined effect of flux pinning by three-directional columnar defects in a field-angular region of high-$$T_{rm c}$$ superconductors

Sueyoshi, Tetsuro*; Enokihata, Ryusei*; Hidaka, Yuka*; Irie, Masahiro*; Fujiyoshi, Takanori*; Okuno, Yasuki*; Ishikawa, Norito

Physica C, 582, p.1353824_1 - 1353824_5, 2021/03

 Times Cited Count:1 Percentile:8.34(Physics, Applied)

We investigated the combined effect of flux pinning by three-directional columnar defects (CDs) in a wide field-angular range of YBa$$_{2}$$Cu$$_{3}$$Oy thin films, where CDs parallel to the $$c$$-axis and CDs crossing at $$pm$$$$theta$$ ($$theta$$=45$$^{circ}$$, 60$$^{circ}$$ and 80$$^{circ}$$) relative to the c-axis were installed by 200 MeV Xe-ion irradiations. The three-directional CDs with $$theta$$$$leqq$$$$pm$$60$$^{circ}$$ form a field angular curve of critical current density Jc with a broad peak centered at magnetic field (B) parallel to the $$c$$-axis, whereas the Jc shows no peaks around the crossing angles of $$pm$$$$theta$$. When the crossing angle is expanded to $$theta$$=$$pm$$80$$^{circ}$$, a drastic change in the field- angular behavior of Jc is induced: there is not a large enhancement of $$J_{rm c}$$ around B//c. We also demonstrated that the combined configuration consisting of CDs at $$theta$$= 0$$^{circ}$$, $$pm$$45$$^{circ}$$, $$pm$$60$$^{circ}$$ and $$pm$$80$$^{circ}$$ provides a uniform enhancement of $$J_{rm c}$$ over a wide angular-region.

Journal Articles

Degradation prediction using displacement damage dose method for AlInGaP solar cells by changing displacement threshold energy under irradiation with low-energy electrons

Okuno, Yasuki*; Ishikawa, Norito; Akiyoshi, Masafumi*; Ando, Hirokazu*; Harumoto, Masaki*; Imaizumi, Mitsuru*

Japanese Journal of Applied Physics, 59(7), p.074001_1 - 074001_7, 2020/07

 Times Cited Count:3 Percentile:20(Physics, Applied)

Performance degradation prediction for space solar cells under irradiation with low-energy electrons is greatly affected by displacement threshold energy (Ed) when a displacement damage dose (DDD) model is used. According to recent studies, the Ed of P atoms is much lower than the conventional Ed value in InP-type solar cells irradiated with low-energy electrons. This indicates that the value of Ed typically used in DDD model leads to significant error in performance degradation prediction. In this study, degradation of AlInGaP solar cells is observed after irradiation with 60 keV electrons. The results suggest that the Ed of P atoms in AlInGaP solar cells is much smaller than the conventionally used Ed value. By using the DDD model with the Ed value obtained in this study, we demonstrated that the performance degradation predicted by the DDD model agrees well with the experimental results.

Journal Articles

Degradation prediction of a gamma-ray radiation dosimeter using InGaP solar cells in a primary containment vessel of the Fukushima Daiichi Nuclear Power Station

Okuno, Yasuki; Yamaguchi, Masafumi*; Okubo, Nariaki; Imaizumi, Mitsuru*

Journal of Nuclear Science and Technology, 57(4), p.457 - 462, 2020/04

 Times Cited Count:7 Percentile:62.49(Nuclear Science & Technology)

Indium gallium phosphide (InGaP) solar cell with a superior high-radiation resistance is expected to be a powerful candidate for a dosimeter under a high-radiation dose rate environment. In this study, in order to predict the lifetime as the dosimeter using the InGaP solar cell, we clarify the effect of minority-carrier diffusion length ($$L$$) on a radiation-induced current as a dose signal in the InGaP solar cell by irradiation tests and empirical calculations. In the irradiation tests, the short circuit current density ($$J_{rm sc}$$) as a function of the gamma-ray dose rate is measured to estimate the $$L$$ for the InGaP solar cell by irradiation tests. The operational lifetime as a detector using the InGaP solar cell under various dose rates is estimated by using the empirical calculations based on the relation between the L and absorbed dose. The results suggest that the dosimeter using InGaP solar cell is able to be used during more than 10 h in the primary containment vessel of the Fukushima Daiichi Nuclear Power Plant and it has a high potential of being a radiation-resistant dosimeter that would contribute to the decommissioning.

Journal Articles

Application of InGaP space solar cells for a radiation dosimetry at high dose rates environment of Fukushima Daiichi Nuclear Power Plant

Okuno, Yasuki; Okubo, Nariaki; Imaizumi, Mitsuru*

Journal of Nuclear Science and Technology, 56(9-10), p.851 - 858, 2019/09

 Times Cited Count:12 Percentile:75.06(Nuclear Science & Technology)

Decommissioning the Fukushima Daiichi Nuclear Power Plant (1F) after the accident caused by a tsunami in 2011 requires characterization of the fuel debris by dose distribution measurement. This paper describes the experimental and theoretical behavior of a radiation detector applied with InGaP solar cells is investigated and allow the localization and characterization of the fuel debris. In the irradiation test, it was observed that the radiation-induced current output of the InGaP solar cells increases linearly with increasing dose rates of $$^{60}$$Co $$gamma$$-ray. For measurements at low dose rates, it becomes clear that the minimum detectable dose rate and resolution can be determined by analyzing the noise characterization. The maximum detection limit of radiation dosimetry for the InGaP solar cell was found to be higher than the highest $$gamma$$-ray dose rate observable at the reactor core for 1F plants. Additionally, as an analysis of the radiation-induced current, it is attempted to express a relational expression between the absorbed dose rate and the creation of radiation-induced current pairs in the solar cells. The experimental and simulation results suggest that solar cells can be powerful tools for radiation dosimetry in high dose rate environments near the debris of the 1F plant.

Journal Articles

Influence of gamma-ray irradiation on mechanical property of YSZ for oxygen sensors in ADS

Okubo, Nariaki; Okuno, Yasuki; Kitamura, Akane; Taguchi, Tomitsugu*

Nuclear Instruments and Methods in Physics Research B, 435, p.198 - 202, 2018/11

 Times Cited Count:2 Percentile:21.23(Instruments & Instrumentation)

Accelerator driven system (ADS) adopts the lead-bismuth eutectic (LBE) as both coolant and spallation target. The oxygen concentration control is one of the most important technical developments. Estimation of durability under gamma-ray irradiation for the oxygen sensor is necessary for the integrity evaluation of ADS components. The Zirconia added by Yttria (YSZ) is the main element in oxygen sensor. Effect of gamma-ray irradiation on the mechanical property and structural change for three types of YSZ with 3, 6, 8 mol% Yttria was evaluated by using 4 points bend test, XRD, SEM and Raman spectroscope. The gamma-ray irradiations were conducted at 1 and 2 kGy/h, which corresponded to the LBE activity after 1 year ADS operation. In the cases of 8Y and 6Y, degradation of strength was not measured and the fracture surface did not change the morphology. In the case of 3Y, however, the strength did not change but phase transformation from tetragonal to monoclinic crystal structure was observed in XRD results, depending on the irradiation dose. This implies that the gamma-ray irradiation causes the phase transformation in 3Y-YSZ.

Oral presentation

Dosimetry and signal correction by displacement damage dose method using superior radiation-resistance InGaP solar cell

Okuno, Yasuki; Kitamura, Akane; Iwamoto, Yosuke; Okubo, Nariaki; Akiyoshi, Masafumi*; Imaizumi, Mitsuru*; Shibata, Yuichi*; Yamaguchi, Masafumi*

no journal, , 

In the vicinity of the reactor core of TEPCO's Fukushima Daiichi Nuclear Power Plant, it is a very high radiation environment due to the accident. In order to investigate the conditions at the inside of the reactor pressure vessele and the building, the current radiation measuring device has limitations in performance and function. Therefore, a simple and highly radiation-tolerant monitor, which can be used under high radiation dose environment, is required. Solar cells are known to be able to measure doses easily. However, the problem is that signals of dose are degraded by radiation damage. In this study, a measurement method of electric current induced by radiaiton and a signal compensation technique applied by a displacement damage prediction model will be reported by using an InGaP solar cell with a high radiation resistance.

Oral presentation

Clarify of degradation mechanism for yttria-stabilized zirconia by $$gamma$$-ray-induced phase transformation

Okuno, Yasuki; Nakashima, Koji; Kitamura, Akane; Uchibori, Yosuke; Yasuda, Satoshi; Asaoka, Hidehito; Okubo, Nariaki

no journal, , 

no abstracts in English

Oral presentation

Radiation effects of ADS target window materials on liquid metal corrosion

Okubo, Nariaki; Kondo, Keietsu; Kitamura, Akane; Okuno, Yasuki

no journal, , 

Research and development of ADS and TEF-T have been done by JAEA. ADS and TEF-T adopt liquid lead bismuth eutectic (LBE) for both spallation target and coolant for the non-critical core. Irradiation and corrosion behaviors of steel materials in LBE are one of the important issues. High energy proton beam and spallation neutron irradiation will cause high dose of displacement damage and high concentration of transmutation gas, helium and hydrogen, simultaneously, in the target window material. At once, the materials will be influenced by the corrosion and erosion, which depends on the irradiation temperature and oxygen concentration in LBE, under LBE flow. Then, the irradiation data for material properties of corrosion/erosion and mechanical changes in flowing LBE is necessary to design and evaluate lifetime of ADS components. It is possible that the TEF-T facility will achieve the irradiation, which covers the ADS conditions of temperature from 450 to 550 and the displacement damage up to 20 dpa as designed for ADS target window. Material issues for the target window, irradiation plan of TEF-T, and the present activities for material test proceeded in static LBE pot and LBE loop systems will be presented.

Oral presentation

Clarification of degradation mechanism for yttria-stabilized zirconia due to $$gamma$$-ray-induced phase transformation

Okuno, Yasuki

no journal, , 

In the accelerator driven system, it is necessary to suppress erosion and corrosion of stainless steel piping by oxygen control of lead bismuth eutectic alloy (LBE). An oxygen sensor using yttria-partially-stabilized zirconia (PSZ) is effective for measuring the oxygen concentration in LBE, and it need to be understood about the influence of radiation during ADS operation. In this study, it was observed that phase transformation from tetragonal to monoclinic crystal occurred when $$^{60}$$Co $$gamma$$-ray was exposed to the PSZ. From the calculation result of the radiation behavior simulation analysis, it has been clarified that this phase transformation was caused by the ionization effect. In this presentation, we report on the phase transformation mechanism of PSZ due to this ionization effect attributed to the radiation.

Oral presentation

Degradation by irradiation with low-energy electrons in AlInGaP solar cell

Okuno, Yasuki; Kitamura, Akane; Ishikawa, Norito; Akiyoshi, Masafumi*; Ando, Hirokazu*; Harumoto, Masaki*; Shibata, Yuichi*; Imaizumi, Mitsuru*; Yamaguchi, Masafumi*

no journal, , 

The displacement damage dose (DDD) for space solar cell is greatly affected by the displacement threshold energy (Ed) during degradation by irradiation with low-energy electrons. In the proposed study, the unpredictable degradation of AlInGaP solar cells in the present DDD model is observed. The findings suggest that the predicted degradation during exposure to low-energy electrons may differ from the actual value. However, it is clarified that if the Ed value is rederived, the nonionizing energy loss can indicate the induced-defect rates in the AlInGaP under irradiation with electrons with a wide range of energy.

Oral presentation

Dependence of displacement threshold energy on materials in compound-semiconductor of InP-type

Okuno, Yasuki; Imaizumi, Mitsuru*

no journal, , 

In the theory of irradiation damage, a primary knock-on-atoms is considered to be generated, if the transferred energy (ET) given to the atom from the radiation by the interaction is larger than displacement threshold energy (Ed). A value of Ed has been conventionally determined by elements, without considering material dependency. In previous research, it was suggested that the Ed of each P in InGaP solar cell was 4 eV instead of 9 eV that has been used in the method of radiation degradation prediction of space solar cell. Additionally, the Ed of P in InP has been calculated to be 7.7 eV in the report by A. Sibille et al.. In the theory of radiation damage, the factor that determines Ed is considered to be a binding energy (EB) and a jumping energy (EJ). The EB value of P in InP and InGaP is calculated as cohesive energy by the first principles calculation based on density functional theory. In the results, it was suggested that EB has no correlation with the Ed value, and has little effect on the one.

Oral presentation

Radiation effects of ADS target window materials on liquid metal corrosion

Okubo, Nariaki; Fujimura, Yuki; Kitamura, Akane; Okuno, Yasuki; Kondo, Keietsu

no journal, , 

An accelerator-driven subcritical reactor is a nuclear reactor design formed by coupling a substantially subcritical nuclear reactor core with a high-energy proton accelerator. In this system, lead-bismuth eutectic (LBE) is supposed to be used as coolant material of reactor core as well as neutron spallation sources. In this study, effect of irradiation on corrosion behavior was evaluated for 316L stainless steel, which is one of candidate ADS target window materials, through the immersion test under LBE with low oxygen concentration followed by ion irradiation experiment.

Oral presentation

Irradiation effects of ADS target window materials on corrosion in liquid metal

Okubo, Nariaki; Fujimura, Yuki; Kitamura, Akane; Okuno, Yasuki

no journal, , 

Japan atomic energy agency has been conducting research activities for developing the accelerator driven system (ADS), which is expected to reduce and transmute radioactive wastes involved in spent fuels by nuclear power plants. The ADS adopts a liquid metal of lead-bismuth eutectic (LBE) as a coolant and also spallation target to produce high energy neutrons. In this study, effect of irradiation on corrosion behavior was evaluated for 316L stainless steel and T91 ferritic martensitic steel, which are candidate materials of ADS target window, through the immersion test under LBE with saturated and low oxygen concentration followed by ion irradiation experiment. In the case of soaking in LBE with saturated oxygen concentration for SS316L steels at 450$$^{circ}$$C, 330 hrs, non-irradiated region did not show clear oxide layer, however, irradiated region showed bi-layers of magnetite and spinel type oxides. The formation rate of oxide layer for irradiated region, 26 $$mu$$m/year, was about twice faster than that of non-irradiated region, 12 $$mu$$m/year. This result suggests that diffusion behavior after irradiation and mass transfer in the interface between LBE and steel surface is important for understanding of irradiation effect on liquid metal corrosion.

Oral presentation

Development of high-level radiation dosimeter by applying solar cells for decommissioning of nuclear reactor

Okuno, Yasuki; Okamoto, Tamotsu*; Goto, Yasuhito*; Akiyoshi, Masafumi*; Imaizumi, Mitsuru*; Kobayashi, Tomohiro*

no journal, , 

A solar cell type detector has features such as a thin film structure and no power supply drive by an internal electric field, and it is considered to be useful in a 1 F decommissioning environment. In this presentation, radiation behavior of InGaP and CdTe solar cells with high radiation resistance are reported.

Oral presentation

Application to radiation dosimeter by using gamma-ray induced current in InGaP solar cells

Okuno, Yasuki; Yamaguchi, Masafumi*; Imaizumi, Mitsuru*

no journal, , 

The InGaP solar cell having superior high radiation resistance is expected to be a powerful candidate for a dosimeter under high radiation dose rate environment. Because the minority carrier diffusion length (L) is a factor determining the solar cell performance and L changes due to radiation damage, it is important to predict the detector performance based on the relationship between L and the absorbed dose. In this study, the effect of L on a radiation-induced current as a dose signal in InGaP solar cell is clarified by irradiation tests and empirical calculations. In order to estimate the L for InGaP solar cell, measuring the short-circuit current density (JSC) as a function of gamma-ray dose rate is conducted. Based on the experimental results and the empirical formula of the relationship between L and JSC, the operational lifetime of the InGaP solar cell detector under various dose rate is estimated and is determined by the cumulative dose. The present result suggests the InGaP solar cell has high potential as a radiation resistant dosimeter for contributing to the decommissioning of the Fukushima Daiichi Nuclear Power Plant.

Oral presentation

Application of InGaP solar cell to dosimeter for alpha-ray

Okuno, Yasuki; Imaizumi, Mitsuru*; Okamoto, Tamotsu*; Kobayashi, Tomohiro*; Akiyoshi, Masafumi*; Goto, Yasuhito*

no journal, , 

In the decommissioning of Fukushima Daiichi Nuclear Power Plant, it is important to specify the distribution and composition of the fuel debris by alpha ray dose analysis. InGaP solar cells is expected to detect alpha-rays because they have the thickness of about one micro meter, which is sufficiently thin with respect to the fly range of alpha-rays. Therefore, the ion irradiation tests with 5 MeV helium was conducted on InGaP solar cells, and the applicability of InGaP solar cells for alpha-ray detector was evaluated and discussed with the results of the experiment and simulation.

Oral presentation

Development of highly radiation-resistant dosimeters that do not require external power source by the application of compound solar cells

Okuno, Yasuki; Imaizumi, Mitsuru*; Okamoto, Tamotsu*; Kobayashi, Tomohiro*; Akiyoshi, Masafumi*; Goto, Yasuhito*

no journal, , 

The Fukushima Daiichi Nuclear Power Station needs to measure the high-level radiation environment near the core, but the ionization chamber, which is the existing product, has limited space where it can be used due to "size", "sensitivity", and "power supply". At present, the information of dose distribution and the estimation of debris position are not sufficiently obtained. Therefore, we have been developing a solar cell type radiation dosimeter as a powerless dosimeter instead of an ionization chamber. In this presentation, we will report on the development of a solar cell self-induced current dosimeter based on the current behavior, degradation behavior, temperature characteristics, etc. that have been elucidated so far.

Oral presentation

Development of prediction accuracy of low energy electron degradation on displacement damage method for next generation AlInGaP space solar cells

Okuno, Yasuki; Imaizumi, Mitsuru*; Akiyoshi, Masafumi*

no journal, , 

For space solar cells, a displacement damage dose (DDD) method is currently being constructed for prediction by radiation degradation. As a next-generation space solar cell, InGaP solar cell, which is the top subcell of the InGaP / GaAs / Ge-3 junction type (3J) solar cell, is considered to replace with AlInGaP solar cell. In previous studies, it was reported that the threshold energy (Ed) of P in InP-based solar cell differs by depending on material. Since Ed affects the degradation prediction in the case of incidention of a low energy particle beam, we analyzed the Ed which enables highly accurate of the degradation prediction in AlInGaP solar cells under low energy electron beam irradiation.

Oral presentation

Development of Al-added high-Mn ODS austenitic steel for liquid metal environment

Kasada, Ryuta*; Wang, H.*; Liu, J.*; Yu, H.*; Kondo, Sosuke*; Okuno, Yasuki*; Okubo, Nariaki; Tokunaga, Toko*; Ono, Naoko*

no journal, , 

With the aim of applying to materials in accelerator driven systems (ADS) core and advanced blankets of fusion systems, a Fe-Mn-Cr-Al-C steel, low-activation austenitic steel, and its oxide dispersion-strengthened (ODS) alloy have been developing. By reviewing the composition of Fe-Cr-Mn-based low-activation austenitic steel that was once examined, the ODS alloy has become a material design that is conscious of twinning induced plasticity (TWIP) steel used as an automobile steel plate, and it aims to improve high temperature strength characteristics and irradiation resistance by ODS. This presentation shows the initial result of the influence of ODS on the strength characteristics and lead bismuth corrosion on the alloy design policy and materials prototyped at the laboratory level. In addition, some issues for application to advanced fusion system blankets are also discussed.

21 (Records 1-20 displayed on this page)