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.
Naoe, Takashi; Kogawa, Hiroyuki; Tanaka, Nobuatsu*; Futakawa, Masatoshi
Advanced Experimental Mechanics, 4, p.17 - 21, 2019/08
We have introduced the following two techniques to mitigate the pressure wave-induced cavitation damage in the mercury target. One is the gas microbubble injection into the flowing mercury, and the other is the double-walled structure with a narrow gap channel at the proton beam entrance portion of the mercury vessel. The latter is expected to mitigate the cavitation damage due to the high-speed liquid flow ( 4 m/s) and the narrow gap boundary (2 mm). To quantitatively investigate the effect of double-walled structure on cavitation damage, cavitation damage tests were conducted by parametrically changing mercury flow velocity and gap width of the channel wall. The results showed that the damage evaluated as a surface roughness was reduced by increasing the flow velocity. By contrast, the effect of gap width on cavitation damage was hardly observed under flowing conditions.
Kawamura, Shunsuke; Naoe, Takashi; Ikeda, Tsubasa*; Tanaka, Nobuatsu*; Futakawa, Masatoshi
Advanced Experimental Mechanics, 4, p.33 - 37, 2019/08
A mercury enclosure vessel made of stainless steel is used as a spallation target in the pulsed spallation neutron source at J-PARC. It is severely damaged by the cavitation induced with pressure waves in association with the pulsed proton beam injection. A double-walled structure with a narrow mercury channel was adopted in the front end of the target vessel to reduce the cavitation damage. It has been experimentally demonstrated that the cavitation damage could be mitigated in the narrow channel but its mechanism has been unclarified yet. In this study, we investigated the cavitation from growing to collapsing through visualizing the spark-induced cavitation bubbles under flow field using a high-speed video camera. Furthermore, we measured the wall vibration due to the cavitation bubble collapse with changing flow velocity parametrically. It was found that the microjet collided perpendicular to the wall in the stagnant flow condition while it collided with an inclined angle from the perpendicular direction, suggesting that the collision pressure on the wall was reduced by flowing.
Wan, T.; Naoe, Takashi; Kogawa, Hiroyuki; Futakawa, Masatoshi; Obayashi, Hironari; Sasa, Toshinobu
Materials, 12(4), p.681_1 - 681_15, 2019/02
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.
Wan, T.; Obayashi, Hironari; Sasa, Toshinobu
NEA/CSNI/R(2017)2 (Internet), p.117 - 127, 2017/06
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.
Ito, Kei; Ezure, Toshiki; Ohshima, Hiroyuki; Kawamura, Takumi*; Nakamine, Yoshiaki*
Proceedings of 9th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-9) (CD-ROM), 6 Pages, 2014/11
The authors have been studied the vortex cavitation in sodium-cooled fast reactors. In this paper, the authors present a modified evaluation method for vortex cavitation, in which a surface tension is modeled mechanistically. Namely, the cavity radius is calculated in consideration of radial pressure distribution, saturated vapor pressure and the pressure jump condition at an interface. As the basic validation of the developed surface tension model, numerical analyses of a simple experiment under various velocity conditions are performed. The evaluation results give qualitatively appropriate tendency, that is, the cavity radius becomes larger with the higher liquid velocity and/or lower reference pressure which cause the larger pressure drop at the vortex. In addition, the authors evaluate the influence of the kinematic viscosity which plays an important role in the vortex cavitation occurrences in the experiments.
Naoe, Takashi; Futakawa, Masatoshi; Oi, Toshiyuki; Ishikura, Shuichi*; Ikeda, Yujiro
Zairyo, 54(11), p.1184 - 1190, 2005/11
High power spallation targets for neutron sources are being developed in the world. Mercury target will be installed at the material science and life facility in J-PARC, which will promote innovative science. The mercury target is subject to the pressure wave caused by the proton bombarding in the mercury. The pressure wave propagation induces the cavitation in mercury that imposes localized impact damage on the target vessel. The impact erosion is a critical issue to decide the lifetime of the target. The electro Magnetic IMpact Testing Machine, MIMTM, was developed to reproduce the localized impact erosion damage and evaluate the damage formation. Additionally, droplet impact analysis was carried out to investigate the correlation between isolate pit profile and micro-jet velocity. We confirmed that value of depth/radius was able to estimate micro jet-velocity. And the velocity at 560W in MIMTM was estimated to be 225325 m/s. Furthermore, surface-hardening treatments were inhibited pit formation in plastic deformation.
Futakawa, Masatoshi; Naoe, Takashi*; Kogawa, Hiroyuki; Date, Hidefumi*; Ikeda, Yujiro
JSME International Journal, Series A, 48(4), p.234 - 239, 2005/10
Mercury target will be installed at the material science and life facility in J-PARC, which will promote innovative science. The mercury target will be subjected to the pressure wave caused by proton bombarding in the mercury. The pressure wave propagation induces the cavitation in mercury that imposes localized impact damage on the target vessel. The impact erosion is a critical issue to decide the lifetime of target. An electromagnetic impact testing machine, MIMTM, was developed to reproduce the localized impact erosion damage and evaluate the damage formation. Additionally, droplet impact analyses were carried out to investigate the correlation between isolate pit profile and micro-jet velocity. We confirmed that the value of depth/radius was applicable to estimate micro-jet velocity, and the velocity at 560 W in MIMTM equivalent to 1MW proton beam injection was 300 m/s approximately.
Naoe, Takashi*; Futakawa, Masatoshi; Koyama, Tomofumi*; Kogawa, Hiroyuki; Ikeda, Yujiro
Jikken Rikigaku, 5(3), p.280 - 285, 2005/09
no abstracts in English
Soyama, Hitoshi*; Futakawa, Masatoshi; Homma, Kana*
Journal of Nuclear Materials, 343(1-3), p.116 - 122, 2005/08
In order to estimate life time of the mercury target vessel of spallation neutron source which will be subjected to cavitation impacts, prediction methods of pitting damage induced by the cavitation impact were proposed. It is very important to estimate incubation time, in which plastic deformation occurs without mass loss, because the thickness of vessel is very thin. In the present paper, two estimation methods were proposed. One of them is estimatiion from erosion test of severely damaged specimen by plotting the mass loss as a function of exposure time to cavitation on the logarithmic scales. Another method is the observation method of plastic deformation pits on damaged surface at very early period in incubation stage.
Koppitz, T.*; Jung, P.*; Mller, G.*; Weisenburger, A.*; Futakawa, Masatoshi; Ikeda, Yujiro
Journal of Nuclear Materials, 343(1-3), p.92 - 100, 2005/08
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.
Futakawa, Masatoshi; Naoe, Takashi*; Kogawa, Hiroyuki; Ikeda, Yujiro
Journal of Nuclear Science and Technology, 41(11), p.1059 - 1064, 2004/11
High power spallation targets for neutron sources are developing in the world. Mercury target will be installed at the material and life science facility in J-PARC, which will promote innovative science. The mercury target is subject to the pressure wave caused by the proton bombarding mercury. The pressure wave propagation induces the cavitation in mercury that imposes localized impact damage on the target vessel. The impact erosion is a critical issue to decide the lifetime of the target. The electric Magnetic Impact Testing Machine, MIMTM, was developed to produce the localized impact erosion damage and evaluate the damage formation. Acoustic vibration measurement was carried out to investigate the correlation between damage and acoustic vibration. It was confirmed that the acoustic vibration is useful to predict the damage due to the localized impact erosion and to diagnose the structural integrity.
Soyama, Hitoshi*; Futakawa, Masatoshi
Tribology Letters, 17(1), p.27 - 30, 2004/07
Estimation have been made, resulting in a general method for the prediction of the incubation time for cavitation erosion using various cavitating conditions and materials. From a single erosion test, the incubation time can be estimated for various conditions and materials by plotting the mass loss as a function of exposure time to cavitation on a log-log scale.
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; Haga, Katsuhiro; Kaminaga, Masanori; Hino, Ryutaro
JAERI-Tech 2003-093, 55 Pages, 2004/01
To estimate the structural integrity of the heavy liquid-metal (Hg) target used in a MW-class neutron scattering facility, static and dynamic stress behaviors due to the incident of a 1MW-pulsed proton beam were analyzed. In the analyses, two-type target containers with semi-cylindrical type and flat type window were used as analytical models of the structural analysis codes LS-DYNA. As a result, it is confirmed that the stress generated by dynamic thermal shock becomes the largest at the center of window, and the flat type window is more advantageous from the structural viewpoint than the semi-cylindrical type window. It was confirmed to erosion damage the target container by mercury's becoming negative pressure in the window and generating the cavitation by the experiment. Therefore, it has been understood that the point top of the window was in the compression stress field by the steady state thermal stress because of the evaluation from destroying the dynamic viewpoint for the crack in the generated pit and the pit point, and the crack did not progress.
Futakawa, Masatoshi; Naoe, Takashi; Kogawa, Hiroyuki; Tsai, C.-C.*; Ikeda, Yujiro
Journal of Nuclear Science and Technology, 40(11), p.895 - 904, 2003/11
A liquid-mercury target system for the MW-scale target is being developed in the world. The pitting damage induced by pressure wave propagation gets to be one of critical issues to estimate the life of the target structure with mercury and to evaluate its structural integrity. The off-line test on the pitting damage at high cycles over 10 millions was carried out using a novel device, the MIMTM which drives electromagnetically to impose pulse pressure into the mercury. It was found that from the pitting damage data obtained by the MIMTM that the pitting damage can be characterized in two steps, an incubation period that can extend to more than 106 cycles in 316SS and 107 cycles in surface hardening treated one and steady state erosion where mass loss scales with the number of cycles to approximately the 1.27 power for mercury. The length of the incubation period is primarily a function of the material and the intensity of the pressure. This observation provides a simple model for estimating lifetime for different materials and beam power.