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Ariyoshi, Gen; Saruta, Koichi; Kogawa, Hiroyuki; Futakawa, Masatoshi; Maeno, Koki*; Li, Y.*; Tsutsui, Kihei*
Proceedings of 20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-20) (Internet), p.1407 - 1420, 2023/08
Cavitation damage on a target vessel due to proton beam-induced pressure waves is one of the crucial issues for the pulsed neutron source using a mercury spallation target. As a mitigation technique for the damage, the helium microbubble injection into the mercury has been carried out by using a swirl bubbler in order to utilize compressibility of bubbles. Moreover, double-walled structure, which consists of an outer wall and an inner wall, has been applied as the target head structure. In this study, we aim to develop an abnormality diagnostic technology to detect the inner wall cracking, which is caused by such cavitation damage, from the outside of the target vessel. The mercury flow fields in the case with the cracking are evaluated by computational fluid dynamics analysis based on finite element method. And then, effect of the cracking on the flow field is discussed from the point of view of the flow-induced vibration and the acoustic vibration.
Naoe, Takashi; Kinoshita, Hidetaka; Kogawa, Hiroyuki; Wakui, Takashi; Wakai, Eiichi; Haga, Katsuhiro; Takada, Hiroshi
Materials Science Forum, 1024, p.111 - 120, 2021/03
The mercury target vessel for the at the J-PARC neutron source is severely damaged by the cavitation caused by proton beam-induced pressure waves in mercury. To mitigate the cavitation damage, we adopted a double-walled structure with a narrow channel for the mercury at the beam window of the vessel. In addition, gas microbubbles were injected into the mercury to suppress the pressure waves. The front end of the vessel was cut out to inspect the effect of the damage mitigation technologies on the interior surface. The results showed that the double-walled target facing the mercury with gas microbubbles operating at 1812 MWh for an average power of 434 kW had equivalent damage to the single-walled target without microbubbles operating 1048 MWh for average power of 181 kW. The erosion depth due to cavitation in the narrow channel was clearly smaller than it was on the wall facing the bubbling mercury
Naoe, Takashi; Kinoshita, Hidetaka; Kogawa, Hiroyuki; Wakui, Takashi; Wakai, Eiichi; Haga, Katsuhiro; Takada, Hiroshi
JPS Conference Proceedings (Internet), 28, p.081004_1 - 081004_6, 2020/02
The beam window of the mercury target vessel in J-PARC is severely damaged by the cavitation. The cavitation damage is a crucial factor to limit lifetime of the target because it increases with the beam power. Therefore, mitigating cavitation damage is an important issue to operate the target stably for long time at 1 MW. At J-PARC, to mitigate the cavitation damage: gas microbubbles are injected into mercury for suppressing pressure waves, and double-walled structure with a narrow channel of 2 mm in width to form high-speed mercury flow (
4m/s) has been adopted. After operation, the beam window was cut to inspect the effect of the cavitation damage mitigation on inner wall. We optimized cutting conditions through the cold cutting tests, succeeding in cutting the target No.2 (without damage mitigation technologies) smoothly in 2017, and target No.8 with damage mitigation technologies. In the workshop, progress of cavitation damage observation for the target vessel will be presented.
Wan, T.; Naoe, Takashi; Kogawa, Hiroyuki; Futakawa, Masatoshi; Obayashi, Hironari; Sasa, Toshinobu
Materials, 12(4), p.681_1 - 681_15, 2019/02
Times Cited Count：3 Percentile：17.62(Chemistry, Physical)Takada, Hiroshi
Plasma and Fusion Research (Internet), 13(Sp.1), p.2505013_1 - 2505013_8, 2018/03
The pulsed spallation neutron source of Japan Proton Accelerator Research Complex (J-PARC) has been supplying users with high intensity and sharp pulse cold neutrons using the moderators with following distinctive features; (1) 100% para-hydrogen for increasing pulse peak intensity with decreasing pulse tail, (2) cylindrical shape with 14 cm diam.
12 cm long for providing high intensity neutrons to wide neutron extraction angles of 50.8
, (3) neutron absorber made from Ag-In-Cd alloy to make pulse width narrower and pulse tails lower. Actually, it was measured at a low power operation that high neutron intensity of 4.510
n/cm
/s/sr could be emitted from the coupled moderator surface for 1-MW operation, and a superior resolution of 
d/d = 0.035% was achieved at a beamline (BL8) with a poisoned moderator, where d is the d-spacing of reflection. Towards the goal to achieve the target operation at 1-MW for 5000 h in a year, technical developments to mitigate cavitation damages on the target vessel with injecting gas micro-bubbles into mercury target and design improvement of target vessel structure to reducing welds and bolt connections as much as possible are under way.
Takada, Hiroshi; Haga, Katsuhiro; Teshigawara, Makoto; Aso, Tomokazu; Meigo, Shinichiro; Kogawa, Hiroyuki; Naoe, Takashi; Wakui, Takashi; Oi, Motoki; Harada, Masahide; et al.
Quantum Beam Science (Internet), 1(2), p.8_1 - 8_26, 2017/09
At the Japan Proton Accelerator Research Complex (J-PARC), a pulsed spallation neutron source provides neutrons with high intensity and narrow pulse width to promote researches on a variety of science in the Materials and life science experimental facility. It was designed to be driven by the proton beam with an energy of 3 GeV, a power of 1 MW at a repetition rate of 25 Hz, that is world's highest power level. A mercury target and three types of liquid para-hydrogen moderators are core components of the spallation neutron source. It is still on the way towards the goal to accomplish the operation with a 1 MW proton beam. In this paper, distinctive features of the target-moderator-reflector system of the pulsed spallation neutron source are reviewed.
Takada, Hiroshi; Naoe, Takashi; Kai, Tetsuya; Kogawa, Hiroyuki; Haga, Katsuhiro
Proceedings of 12th International Topical Meeting on Nuclear Applications of Accelerators (AccApp '15), p.297 - 304, 2016/00
In J-PARC, we have continuously been making efforts to operate a mercury target of a pulsed spallation neutron source with rated power of 1-MW. One of technical progresses is to mitigate cavitation damages at the target vessel front induced by the 3-GeV proton beam injection at 25 Hz. We have improved the performance of a gas micro-bubbles injection into the mercury target, resulting that no significant cavitation damages was observed on the inner surface of target vessel after operation for 2050 MWh with the 300-kW proton beam. Another progress is to suppress the release of gaseous radioactive isotopes, especially tritium, during the target vessel replacement. We have introduced a procedure to evacuate the target system by an off-gas processing apparatus when it is opened during the replacement operation, achieving to suppress the tritium release through the stack. For example, the amount of released tritium was 12.5 GBq, only 5.4% of the estimated amount, after the 2050 MWh operation. After these progresses, the operating beam power for the pulsed spallation neutron source was ramped up to 500-kW in April, 2015.
Koppitz, T.*; Jung, P.*; M
ller, G.*; Weisenburger, A.*; Futakawa, Masatoshi; Ikeda, Yujiro
Journal of Nuclear Materials, 343(1-3), p.92 - 100, 2005/08
Times Cited Count：7 Percentile：44.84(Materials Science, Multidisciplinary)Cavitation damage of structural materials due to pressure waves is expected to be one of the majior life-time limiting factors in high power liquid metal spallation targets under pulsed operation. Two methods are developed for the European Spallation Source (ESS) to mitigate this damage: Introduction of gas bubbles to surpress the pressure pulse and surface-hardening of structural materials. Surface-hardening of four 8-13%Cr martenstic steels was examined by thermal treatment with pulsed or scanned electron- and laser-beams as well as by nitriding in plasma. A specimens of the 12%Cr steel were tested in liquid mercury under pulsed proton irradiation, and under mechanical pulsed-loading. Surface damage was analysed by optical, confocal-laser, or scanning-electron microscopy, showing in both tests much better resistance of the hardened material compared to standard condition.
Ishikura, Shuichi*; Kogawa, Hiroyuki; Futakawa, Masatoshi; Kaminaga, Masanori; Hino, Ryutaro; Saito, Masakatsu*
Nihon Genshiryoku Gakkai Wabun Rombunshi, 3(1), p.59 - 66, 2004/03
The development of a MW-class spallation neutron source facility is being carried out under the Japan Proton Accelerator Research Complex (J-PARC) Project promoted by JAERI and KEK. A mercury target working as the spallation neutron source will be subjected to pressure waves generated by rapid thermal expansion of mercury due to a pulsed proton beam injection. The pressure wave will impose dynamic stress on the vessel and deform the vessel, which would cause cavitation in mercury. To evaluate the effect of mercury micro jets, driven by cavitation bubble collapse, on the micro-pit formation, analyses on mercury sphere collision were carried out: single bubble dynamics and collision behavior on interface between liquid and solid, which take the nonlinearity due to shock wave in mercury and the strain rate dependency of yield stress in solid metal into account. Analytical results give a good explanation to understand relationship between the micro-pit formation and material properties: the pit size could decrease with increasing the yield strength of materials.
Ishikura, Shuichi*; Kogawa, Hiroyuki; Futakawa, Masatoshi; Kikuchi, Kenji; Hino, Ryutaro; Arakawa, Chuichi
Journal of Nuclear Materials, 318, p.113 - 121, 2003/05
Times Cited Count：12 Percentile：62.16(Materials Science, Multidisciplinary)The thermal shock stress in the mercury target vessel was analyzed: the target receives the incident proton beam at the energy of 1 MW with the pulse duration of 1ms. Negative pressure of maximal 61MPa was generated when the initial pressure of 52MPa propagated in mercury. It is expected then that the cavitation may be arisen by the negative pressure. So in order to know the cavitation behavior, the simulation study was carried out by using the equation of motion based on the bubble dynamics for a single bubble, and fundamental parameter analysis was carried out. It is found that a bubble has a potential expansion more than 1000 times with a change of the pressure at the window of the target vessel. Consequently wave propagation will be affected. Theoretical consideration was given to the wave motion of propagation in bubbly liquid. The equation of state in bubbly liquid can be approximated by the polynomial. The diameter of a bubble and the bubble volume fraction inherent in mercury can be decided if the critical pressure, the sound velocity, and resonance frequency is successfully measured by static and dynamic experiment.
Ikeda, Tsubasa; Kogawa, Hiroyuki; Naoe, Takashi; Kawamura, Shunsuke; Tanaka, Nobuatsu*; Futakawa, Masatoshi
no journal, ,
In the mercury target of the pulsed spallation neutron source at J-PARC, pressure waves are generated by the high-intensity pulsed-proton beam bombardment, resulting in inducing cavitation. Because the cavitation causes severe erosion damages on the mercury enclosure vessel made of stainless steel, suppressing the pressure waves and the cavitation are crucial issues to realize stable target operations at rated proton beam power of 1 MW. Gas microbubbles injection into flowing mercury is one of the prospective techniques to suppress pressure waves. At the J-PARC, a swirl-flow bubble-generator has been developed to generate microbubbles and installed in the mercury target. In order to improve the performance of the pressure wave suppression by increasing the amount of microbubbles, effects of the vane angle and throttling ratio of the Venturi on the amount of microbubbles were parametrically investigated through water experiments. The experimental results showed that the amount of the microbubbles was increased with decreasing the throttling ratio of the Venturi.
Kawamura, Shunsuke; Naoe, Takashi; Tanaka, Nobuatsu*; Futakawa, Masatoshi
no journal, ,
In the mercury target for the pulsed spallation neutron source at J-PARC, cavitation damage at the beam window of the mercury target vessel is a key factor to decide lifetime of target because the damage degrade the vessel structural integrity. A double-walled structure with a narrow channel was adopted to the vessel for expecting to reduce cavitation damage. In this study, the cavitation bubble behaviors of the growth and collapse under water flow field were investigated to determine the effective factor for mitigating cavitation damage in narrow channel. We measured the equivalent diameter and wall vibration due to the cavitation bubble collapse with parametrically changing flow velocity. It was found that the maximum equivalent diameter of the cavitation bubble and the response vibrational acceleration of the wall are decreased with the increasing velocity. As the results, it was found that cavitation bubble collapse pressure was affected by flowing condition in the narrow channel.
Ariyoshi, Gen; Ito, Kei*; Kogawa, Hiroyuki; Futakawa, Masatoshi
no journal, ,
Cavitation damage caused by pressure waves is one of the important issues which threaten the integrity of the mercury spallation target vessel in J-PARC. To mitigate the damage, technology using mercury-helium two-phase flow has been developed. Although effective bubble radius for absorption/attenuation of the waves is evaluated as less than 0.1 mm, actual bubble radius might be different from the evaluated one due to microbubble coalescence phenomena. Therefore, the purpose of present study is to clarify and predict the bubble radius distribution in the target. To achieve that, visualization of microbubble coalescence phenomena was performed by using air-water two-phase flow as a model flow. Obtained experimental results and numerical prediction code presently developed will be explained.
