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JAEA Reports

Experimental study on prevention of high cycle thermal fatigue at the core outlet of advanced sodium-cooled fast reactor; Characteristics of temperature fluctuations and countermeasures to mitigate temperature fluctuations at a bottom of upper internal structure

Kobayashi, Jun; Aizawa, Kosuke; Ezure, Toshiki; Nagasawa, Kazuyoshi*; Kurihara, Akikazu; Tanaka, Masaaki

JAEA-Research 2022-009, 125 Pages, 2023/01

JAEA-Research-2022-009.pdf:29.22MB

The design studies of an advanced loop-type sodium-cooled fast reactor (Advanced- SFR) have been carried out by the Japan Atomic Energy Agency (JAEA). At the core outlet, temperature fluctuations occur due to mixing of hot sodium from the fuel assembly with cold sodium from the control rod channels and radial blanket assembly. These temperature fluctuations may cause high cycle thermal fatigue around a bottom of Upper Internal Structure (UIS) located above the core. Therefore, we conducted a water experiment using a 1/3 scale 60 degree sector model that simulated the upper plenum of the advanced loop-type sodium-cooled reactor. And we proposed some countermeasures against large temperature fluctuations that occur at the bottom of the UIS. In this report, we have summarized that the effect of the countermeasure structure to mitigate the temperature fluctuation generated at the bottom of UIS is confirmed, and the Reynolds number dependency of the countermeasure structure and the characteristics of the temperature fluctuation on the control rod surface.

Journal Articles

Investigation on natural circulation behavior for decay heat removal in reactor vessel of sodium-cooled fast reactor under severe accident condition, 2; Transient behavior under operations of multiple decay heat removal systems

Aizawa, Kosuke; Tsuji, Mitsuyo; Kobayashi, Jun; Kurihara, Akikazu

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 7 Pages, 2022/10

In sodium-cooled fast reactors (SFRs), optimizing the design and operate decay heat removal systems (DHRSs) is important for safety enhancement against severe accidents. Thus, it is required to evaluate the cooling capability of DHRSs including the natural circulation behavior inside the reactor vessel during heat-removal phase that the fuel debris relocated in the reactor vessel is cooled by DHRSs. In this study, the experiments which simultaneously operations of the dipped-type DHX and the penetrated-type DHX were conducted to investigate the effect of operating multiple decay heat removal system on the natural circulation behavior in the reactor vessel. After achieving the stable conditions by operating the dipped-type DHX or the penetrated-type DHX, the other DHX was operated and the transient behavior was clarified by the temperature measurements. The clear temperature rise in the reactor vessel was confirmed by operating the penetrated-type DHX as second DHX operation under the condition of the dipped-type DHX operation at the beginning and the high heater power of fuel debris on the core catcher. Therefore, it was confirmed that the inhibition of the cooling for the decay heat occurred by operating multiple DHXs.

Journal Articles

Investigation on natural circulation behavior for decay heat removal in reactor vessel of sodium-cooled fast reactor under severe accident condition, 1; Effect of decay-heat conditions on natural circulation behavior under dipped-type DHX operation conditions

Tsuji, Mitsuyo; Aizawa, Kosuke; Kobayashi, Jun; Kurihara, Akikazu

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 6 Pages, 2022/10

In sodium-cooled fast reactors (SFRs), decay heat removal after a core disruptive accident (CDA) is an important issue for the safety enhancement. Therefore, water experiments using a 1/10 scale experimental apparatus (PHEASANT) that simulates the reactor vessel of an SFR are conducted to investigate the natural circulation phenomena in the reactor vessel. In this study, experiments under the operation of the dipped-type DHX were conducted to investigate the effect of the heat generation ratio between the fuel debris on the core catcher in lower plenum and the reactor core remnant on the natural circulation behavior in the reactor vessel. The temperature distribution and the velocity distribution were measured under two heat generation conditions. Thus, the effect of the heat generation ratio between the fuel debris in the lower plenum and the reactor core remnant on the natural circulation behavior was quantitatively grasped under the dipped-type DHX operating conditions.

Journal Articles

Hydrogen absorption and diffusion behaviors in cube-shaped palladium nanoparticles revealed by ambient-pressure X-ray photoelectron spectroscopy

Tang, J.*; Seo, O.*; Rivera Rocabado, D. S.*; Koitaya, Takanori*; Yamamoto, Susumu*; Namba, Yusuke*; Song, C.*; Kim, J.*; Yoshigoe, Akitaka; Koyama, Michihisa*; et al.

Applied Surface Science, 587, p.152797_1 - 152797_8, 2022/06

 Times Cited Count:4 Percentile:94.01(Chemistry, Physical)

The hydrogen absorption and diffusion mechanisms on cube-shaped Pd nanoparticles (NPs) which are important hydrogen-storage materials were studied using X-ray photoelectron spectroscopy and DFT calculations. In the surface region, hydrogen absorption showed almost similar behavior regardless of the NPs size. It was found that the octahedral sites are more favorable than the tetrahedral sites for hydrogen occupation. We also clarified that the hydrogen atoms absorbing on the smaller-sized Pd NPs diffuse to the subsurface more actively because of the weakened Pd-H bond by the surface disordering, which plays an important role in hydrogen adsorption at a low H$$_{2}$$ pressure.

Journal Articles

Investigation on natural circulation for decay heat removal in reactor vessel of sodium-cooled fast reactor

Aizawa, Kosuke; Tsuji, Mitsuyo; Kobayashi, Jun; Kurihara, Akikazu; Miyake, Yasuhiro*; Nakane, Shigeru*; Ishida, Katsuji*

Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Sustainable Clean Energy for the Future (FR22) (Internet), 10 Pages, 2022/04

In sodium-cooled fast reactors (SFRs), optimizing the design and operate decay heat removal systems (DHRSs) is important for safety enhancement against severe accidents that could lead to core melting. The natural circulation phenomena in a reactor vessel during operating a DHRS were clarified by conducting water experiments using a 1:10 scale experimental facility (PHEASANT) simulating the reactor vessel of loop-type SFRs. In this study, we investigated the natural circulation phenomena under conditions of operating the dipped-type DHX and RVACS using the results of temperature and particle image velocimetry (PIV) measurements, respectively. Furthermore, the effects of temperature fluctuation on the PIV measurement were quantitatively evaluated.

JAEA Reports

Noise countermeasures for inverter-controlled multi-stage roots vacuum pumps in J-PARC LINAC L3BT

Takano, Kazuhiro; Kotoku, Hirofumi*; Kobayashi, Fuminori*; Miyao, Tomoaki*; Moriya, Katsuhiro; Kamiya, Junichiro

JAEA-Technology 2021-017, 35 Pages, 2021/11

JAEA-Technology-2021-017.pdf:5.32MB

In J-PARC LINAC, the vacuum system of L3BT, which is a beam transport line connecting LINAC and 3GeV synchrotron, uses a turbo molecular pump and roots pump for rough exhaust and an ion pump for main exhaust. In addition, beam dumps are connected to the end of the L3BT at 0 degree, 30 degree, 90 degree, and 100 degree positions via vacuum partition windows. The roots pumps are used as the exhaust system for each beam dump. The roots pump controllers have been installed away from the pump in the accelerator tunnel to avoid radiation damages. Besides, the special controllers, which have no inverter circuit inside, have been used to reduce the electrical noise on the beam loss monitors nearby. However, using the special controller without inverters, several problems have occurred such as the instability or wide variability of the pumping speed. To solve such problems, the roots pump controller with the inverter circuit must be used after reducing the electrical noise. In this report, some countermeasures to reduce the electrical noise from the inverters were investigated. The noise reduction circuit was successfully optimized to the level where the beam loss monitors works unaffected.

Journal Articles

Water experiments on thermal striping phenomena at the core outlet of an advanced sodium-cooled fast reactor, 1; Proposal of countermeasures to mitigate temperature fluctuations around control rods

Kobayashi, Jun; Aizawa, Kosuke; Ezure, Toshiki; Kurihara, Akikazu; Tanaka, Masaaki

Hozengaku, 20(3), p.89 - 96, 2021/10

Hot sodium from the fuel assembly can mix with cold sodium from the control rod (CR) channel and the blanket assemblies at the bottom plate of the Upper Internal Structure (UIS) of Advanced-SFR. Temperature fluctuation due to mixing of the fluids at different temperature between the core outlet and cold channel may cause high cycle thermal fatigue on the structure around the bottom of UIS. A water experiment using a 1/3 scale 60 degree sector model simulating the upper plenum of the Advanced-SFR has been conducted to examine countermeasures for the significant temperature fluctuation generated around the bottom of UIS. We focused on the temperature fluctuations near the primary and backup control rod channels, and studied the countermeasure structure to mitigate the temperature fluctuation through temperature distribution and flow velocity distribution measurements. As a result, effectiveness of the countermeasure to mitigate the temperature fluctuation intensity was confirmed.

Journal Articles

Water experiments on thermal striping phenomena at the core outlet of an advanced sodium-cooled fast reactor, 2; Proposal of countermeasures to mitigate temperature fluctuations around radial blanket fuel assemblies

Kobayashi, Jun; Aizawa, Kosuke; Ezure, Toshiki; Kurihara, Akikazu; Tanaka, Masaaki

Hozengaku, 20(3), p.97 - 101, 2021/10

Focusing on the thermal striping phenomena that occurs at a bottom of the internal structure of an advanced sodium-cooled fast reactor (Advanced-SFR) that has been designed by the Japan Atomic Energy Agency, a water experiment using a 1/3 scale 60 degree sector model simulating the upper plenum of the Advanced-SFR has been conducted to examine countermeasures for the significant temperature fluctuation generated around the bottom of Upper Internal Structure (UIS). In the previous paper, we reported the effect of measures to mitigate temperature fluctuations around the control rod channels. In this paper, the same test section was used, and a water experiment was conducted to obtain the characteristics of temperature fluctuations around the radial blanket fuel assembly. And the shape of the Core Instrumentation Support Plate (CIP) was modified, and it was confirmed that it was highly effective in alleviating temperature fluctuations around the radial blanket fuel assembly.

Journal Articles

Wettability of pure metals with liquid sodium and liquid tin

Saito, Junichi; Kobayashi, Yohei*; Shibutani, Hideo*

Materials Transactions, 62(10), p.1524 - 1532, 2021/10

 Times Cited Count:2 Percentile:36.58(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Wettability of pure metals with liquid sodium and liquid tin

Saito, Junichi; Kobayashi, Yohei*; Shibutani, Hideo*

Nihon Kinzoku Gakkai-Shi, 85(3), p.110 - 119, 2021/03

 Times Cited Count:0 Percentile:0(Metallurgy & Metallurgical Engineering)

Journal Articles

Quasifree neutron knockout reaction reveals a small $$s$$-Orbital component in the Borromean nucleus $$^{17}$$B

Yang, Z. H.*; Kubota, Yuki*; Corsi, A.*; Yoshida, Kazuki; Sun, X.-X.*; Li, J. G.*; Kimura, Masaaki*; Michel, N.*; Ogata, Kazuyuki*; Yuan, C. X.*; et al.

Physical Review Letters, 126(8), p.082501_1 - 082501_8, 2021/02

AA2020-0819.pdf:1.29MB

 Times Cited Count:24 Percentile:97.02(Physics, Multidisciplinary)

A quasifree ($$p$$,$$pn$$) experiment was performed to study the structure of the Borromean nucleus $$^{17}$$B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for $$1s_{1/2}$$ and $$0d_{5/2}$$ orbitals, and a surprisingly small percentage of 9(2)% was determined for $$1s_{1/2}$$. Our finding of such a small $$1s_{1/2}$$ component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in $$^{17}$$B. The present work gives the smallest $$s$$- or $$p$$-orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of $$s$$ or $$p$$ orbitals is not a prerequisite for the occurrence of a neutron halo.

Journal Articles

Formation of $$alpha$$ clusters in dilute neutron-rich matter

Tanaka, Junki*; Yang, Z.*; Typel, S.*; Adachi, Satoshi*; Bai, S.*; Van Beek, P.*; Beaumel, D.*; Fujikawa, Yuki*; Han, J.*; Heil, S.*; et al.

Science, 371(6526), p.260 - 264, 2021/01

 Times Cited Count:22 Percentile:99.23(Multidisciplinary Sciences)

By employing quasi-free $$alpha$$-cluster-knockout reactions, we obtained direct experimental evidence for the formation of $$alpha$$ clusters at the surface of neutron-rich tin isotopes. The observed monotonous decrease of the reaction cross sections with increasing mass number, in excellent agreement with the theoretical prediction, implies a tight interplay between $$alpha$$-cluster formation and the neutron skin.

Journal Articles

Visualizing cation vacancies in Ce:Gd$$_{3}$$Al$$_{2}$$Ga$$_{3}$$O$$_{12}$$ scintillators by gamma-ray-induced positron annihilation lifetime spectroscopy

Fujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.

Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08

 Times Cited Count:4 Percentile:38.7(Physics, Applied)

To clarify the existence of cation vacancies in Ce-doped Gd$$_{3}$$Al$$_{2}$$Ga$$_{3}$$O$$_{12}$$ (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:Y$$_{3}$$Al$$_{5}$$O$$_{12}$$, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg$$^{2+}$$ ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.

Journal Articles

Ultralow-energy magnon anomaly in yttrium iron garnet

Shamoto, Shinichi; Yasui, Yukio*; Matsuura, Masato*; Akatsu, Mitsuhiro*; Kobayashi, Yoshiaki*; Nemoto, Yuichi*; Ieda, Junichi

Physical Review Research (Internet), 2(3), p.033235_1 - 033235_6, 2020/08

Ultralow energy magnon in yttrium iron garnet crystal has been studied by inelastic neutron scattering in an energy range from 10 to 45 $$mu$$eV. When a magnetic field of about 0.1 T is applied along [111], ultralow energy magnon anomaly is found at 10 K.

Journal Articles

Study on cooling process in a reactor vessel of sodium-cooled fast reactor under severe accident; Velocity measurement experiments simulating operation of decay heat removal systems

Tsuji, Mitsuyo; Aizawa, Kosuke; Kobayashi, Jun; Kurihara, Akikazu; Miyake, Yasuhiro*

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 5 Pages, 2020/08

The water experiments using a 1/10 scale experimental apparatus simulating the reactor vessel of SFR were conducted to investigate the natural circulation phenomena in a reactor vessel. In this paper, the natural circulation flow field in the reactor vessel was measured by the Particle Image Velocimetry (PIV) method. The PIV measurement was carried out under the operation of the dipped-type direct heat exchanger (DHX) installed in the upper plenum when 20% of the core fuel fell to the lower plenum and accumulated on the core catcher. From the results of PIV measurement, it was quantitatively confirmed that the upward flow occurred at the center region of the lower and upper plenums. In addition, the downward flows were confirmed near the reactor vessel wall in the upper plenum and through outermost layer of the simulated core in the lower plenum. Moreover, the relationship between the temperature field and the velocity field was investigated in order to understand the natural circulation phenomenon in the reactor vessel. From the above results, it was confirmed that the natural circulation cooling path was established under the dipped-type DHX operation.

Journal Articles

Effects of temperature fluctuation on PIV measurement of natural circulation flow field

Tsuji, Mitsuyo; Aizawa, Kosuke; Kobayashi, Jun; Kurihara, Akikazu; Miyake, Yasuhiro*

Proceedings of 14th International Symposium on Advanced Science and Technology in Experimental Mechanics (14th ISEM'19) (USB Flash Drive), 4 Pages, 2019/11

The particle image velocimetry (PIV) was measured in scaled-model water experiments simulating a natural circulation flow field in a sodium-cooled fast reactor vessel. The temperature fluctuation in the natural circulation flow field causes the distribution of the refractive index. Thus, the temperature fluctuation affects the uncertainty of the velocity in the PIV measurement. In this study, the authors evaluated the effects of the temperature fluctuation on the PIV measurement in the natural circulation flow field.

Journal Articles

Study on multi-dimensional core cooling behavior of sodium-cooled fast reactors under DRACS operating conditions

Ezure, Toshiki; Onojima, Takamitsu; Tanaka, Masaaki; Kobayashi, Jun; Kurihara, Akikazu; Kameyama, Yuri*

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.3355 - 3363, 2019/08

Steady-state sodium experiments under the operating conditions of a decay heat removal system (DHRS) were carried out as part of the safety enhancement of sodium-cooled fast reactors using the PLANDTL 2 facility, which has 30 heated channels with electric heaters and 25 no-heated channels as the simulated core. In the experiments, a direct reactor auxiliary cooling system (DRACS) with a dipped type direct heat exchanger (DHX) in the upper plenum was used as the DHRS. This paper reports on the preliminary experimental results of the PLANDTL 2 experiments under the DRACS operating conditions without flow in the primary circuit, including the thermal hydraulic interactions between the upper plenum and the core under the DHX operating conditions and the resulting core cooling behavior from the outside of the multiple rows of the fuel assemblies

Journal Articles

Fukushima $$^{137}$$Cs releases dispersion modelling over the Pacific Ocean; Comparisons of models with water, sediment and biota data

Peri$'a$$~n$ez, R.*; Bezhenar, R.*; Brovchenko, I.*; Jung, K. T.*; Kamidaira, Yuki; Kim, K. O.*; Kobayashi, Takuya; Liptak, L.*; Maderich, V.*; Min, B. I.*; et al.

Journal of Environmental Radioactivity, 198, p.50 - 63, 2019/03

 Times Cited Count:14 Percentile:63.62(Environmental Sciences)

A number of marine radionuclide dispersion models were applied to simulate $$^{137}$$Cs releases from Fukushima Daiichi Nuclear Power Plant accident in 2011 over the northwest Pacific. Simulations extended over two years and both direct releases into the ocean and deposition of atmospheric releases on the ocean surface were considered. Dispersion models included an embedded biological uptake model (BUM). Three types of BUMs were used: equilibrium, dynamic and allometric. Model results were compared with $$^{137}$$Cs measurements in water, sediment and biota. A reasonable agreement in model/model and model/data comparisons was obtained.

Journal Articles

Penetration of $$^{129}$$I released from Fukushima Daiichi Nuclear Power Plant accident in the western North Pacific Ocean

Suzuki, Takashi; Otosaka, Shigeyoshi; Kuwabara, Jun; Kawamura, Hideyuki; Kobayashi, Takuya

JAEA-Conf 2018-002, p.103 - 106, 2019/02

To investigate the dynamics of radionuclides in the ocean released by the accident at Fukushima Daiichi Nuclear Power Plant (1F), vertical distributions of $$^{129}$$ I at three stations in the western North Pacific was revealed. The 1F accident-derived $$^{129}$$ I existed within the mixed layer at 3 stations. The maximum layer of the 1F accident-derived $$^{129}$$ I existed at the depth of 370 m - 470 m at the most southern station. Considering the dissolved oxygen concentration and the current velocity arround the station, the maximum layer of the 1F accident-derived $$^{129}$$ I would be fromed that $$^{129}$$I which existed in the surface seawater at other area of observation point was carried to the depth of 370 m - 470 m by the fast downward flow.

Journal Articles

Local structure study of the iron-based systems of BaFe$$_2$$As$$_2$$ and LiFeAs by X-ray PDF and XAFS analyses

Li, S.*; Toyoda, Masayuki*; Kobayashi, Yoshiaki*; Ito, Masayuki*; Ikeuchi, Kazuhiko*; Yoneda, Yasuhiro; Otani, Akira*; Matsumura, Daiju; Asano, Shun*; Mizuki, Junichiro*; et al.

Physica C, 555, p.45 - 53, 2018/12

 Times Cited Count:1 Percentile:6.22(Physics, Applied)

${it T}$-dependence of local distortions in BaFe$$_2$$As$$_2$$ and LiFeAs by X-ray PDF and XAFS methods. Although PDF data exhibit anomaly at the structure transition temperature, EXAFS data exhibit no anomaly. Data supporting the local orthorhombicity at 300 K in the tetragonal phase for BaFe$$_2$$As$$_2$$. Arguments on the origins of the 4-fold symmetry breaking in the ground average structure of the tetragonal phase.

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