Wakui, Takashi; Ishii, Hideaki*; Naoe, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro; Wakai, Eiichi; Takada, Hiroshi; Futakawa, Masatoshi
Materials Transactions, 60(6), p.1026 - 1033, 2019/06
The mercury target has large size as 184.108.40.206 m. In view of reducing the amount of wastes, we studied the structure so that the fore part could be separated. The flange is required to have high seal performance less than 110 Pa m/s. Invar with low thermal expansion is a candidate. Due to its low stiffness, however, the flange may deform when it is fastened by bolts. Practically invar is reinforced with stainless steel where all interface between them has to be bonded completely with the HIP bonding. In this study, we made specimens at four temperatures and conducted tensile tests. The specimen bonded at 973 K had little diffusion layer, and so fractured at the interface. The tensile strength reduced with increasing the temperature, and the reduced amount was about 10% at 1473 K. The analyzed residual stresses near the interface increased by 50% at maximum. Then, we concluded that the optimum temperature was 1173 K.
Naoe, Takashi; Wakui, Takashi; Kogawa, Hiroyuki; Wakai, Eiichi; Haga, Katsuhiro; Takada, Hiroshi
Advanced Experimental Mechanics, 3, p.123 - 128, 2018/08
A mercury target vessel, composed of SUS316L, is used for the pulsed neutron source and is assembled via TIG welding. While in operation, the target vessel suffers ca. 10 loading cycles with a high strain rate of ca. 50 s because of the proton-beam-induced pressure waves in mercury. The gigacycle fatigue strength for solution annealed SUS316L stainless steels and its welded specimens were investigated through ultrasonic fatigue tests. The experimental results showed that an obvious fatigue limit was not observed at fewer than 10 cycles for the base metal. In the case of no weld defects observed via penetration tests, the fatigue strength of the removed-weld-bead specimen, in which the weld lines were arranged at the center of the specimen, appeared to be slightly higher than that of the base metal. By contrast, as-welded specimens with the weld bead intact showed apparent degradation of the fatigue strength owing to the stress concentration around the weld toe.
Naoe, Takashi; Wakui, Takashi; Kinoshita, Hidetaka; Kogawa, Hiroyuki; Haga, Katsuhiro; Harada, Masahide; Takada, Hiroshi; Futakawa, Masatoshi
Journal of Nuclear Materials, 506, p.35 - 42, 2018/08
A mercury target vessel made of 316L SS is damaged due to the cavitation caused by the pressure waves in mercury. Cavitation damage reduces the structural integrity of the target front, called "beam window", being major factor to determine the lifetime of target vessel. Aiming at mitigating the cavitation damage by faster mercury flow in narrow channel, we employed a target vessel with a double-walled structure at the beam window along with a gas microbubbles injection. After operating the double-walled target vessel with a beam power of 300 to 500 kW, we cut out the beam window using an annular cutter to examine the damage inside it, and found that damages with maximum pit depth of approximately 25 m distributed in a belt on the specimen facing narrow channel. Furthermore, numerical simulation result showed that the distribution of negative pressure period from beam injection to 1 ms was correlated with the damage distribution in the narrow channel. It was suggested that the cavitation induced by relatively short negative pressure period contributed to the damage formation.
Kai, Tetsuya; Uchida, Toshitsugu; Kinoshita, Hidetaka; Seki, Masakazu; Oi, Motoki; Wakui, Takashi; Haga, Katsuhiro; Kasugai, Yoshimi; Takada, Hiroshi
Journal of Physics; Conference Series, 1021(1), p.012042_1 - 012042_4, 2018/06
Haga, Katsuhiro; Kogawa, Hiroyuki; Wakui, Takashi; Naoe, Takashi; Takada, Hiroshi
Journal of Nuclear Science and Technology, 55(2), p.160 - 168, 2018/02
The mercury target vessel used for the spallation neutron source in J-PARC has multi-walled structure made of stainless steel type 316L, which comprises a mercury vessel and a water shroud. In 2015, water leak incidents from the water shroud occurred while the mercury target was operated with a proton beam power of 500 kW. Several investigations were conducted to identify the cause of failure. The results of the visual inspections, mockup tests, and analytical evaluations suggested that the water leak was caused by the combination of two factors. One was the diffusion bonding failure due to the large thermal stress induced by welding of the bolt head, which fixes the mercury vessel and the water shroud, during the fabrication process. The other was the thermal fatigue failure of the seal weld due to the repetitive beam trip during the operating period. These target failures point to the importance of eliminating initial defects from welding lines and to secure the rigidity and reliability of welded structures. The next mercury target was fabricated with an improved design which adopted parts of monolithic structure machined by wire EDM to reduce welding lines, and intensified inspections to eliminate the initial defects. The operation with the improved target is planned to be started in October 2017.
Hamon, 27(4), p.155 - 158, 2017/11
The pulsed spallation neutron source driven by a high-power accelerator is one of the most powerful apparatus to provide high intensity and high quality neutrons with narrow pulse width for conducting cutting-edge researches in several domains of materials and life science. In this system, proton beams of several kW to MW order extracted from the high power accelerator is injected into a target, which is heavy metal, to generate vast amount of neutrons via the spallation reactions with the target nuclei, and slows down these neutrons to thermal to cold neutrons with a moderator and a reflector. Resultant neutron beams are then supplied to a suit of the state-of-the-art experimental devices. In this paper, mechanism to produce neutron beams and outline of the spallation neutron source, engineering design of a target system such as a mercury target, and technical topics to solve the pitting damage problem of the target vessel which is caused by the pressure wave of up to 40MPa at maximum generated in the mercury by the pulsed proton beam injection are reviewed by referring mainly to the mercury target system of the pulsed spallation neutron source at J-PARC.
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.
Kogawa, Hiroyuki; Naoe, Takashi; Futakawa, Masatoshi; Haga, Katsuhiro; Wakui, Takashi; Harada, Masahide; Takada, Hiroshi
Journal of Nuclear Science and Technology, 54(7), p.733 - 741, 2017/07
A mercury target system has been operated to produce neutron beams at the spallation neutron source in the Japan Proton Accelerator Research Complex (J-PARC). Pressure waves are generated in mercury by rapid heat generation at the time of high-intensity short-pulse proton beam injection. Not only they cause cyclic stress but also induce the cavitation damage on the target vessel made from type 316L stainless steel. Reduction of these pressure waves is very important issue to ensure enough lifetime of the target vessel. To solve the issue, we have been developing the technique to inject microbubbles into mercury. In this study, we installed a microbubble generator in the mercury target vessel, and investigate the effect of proton beam condition and the microbubbles on the pressure wave mitigation by measuring the displacement velocity of the target vessel with an in-situ diagnostic system. As a result, we observed that the peak displacement velocity of the target vessel decreased down to 1/3 and 2/3 for the injected gas fractions of 0.4% and 0.1%, respectively.
Wan, T.; Naoe, Takashi; Wakui, Takashi; Haga, Katsuhiro; Kogawa, Hiroyuki; Futakawa, Masatoshi
JAEA-Conf 2015-002, p.76 - 87, 2016/02
High power accelerator driven pulsed spallation neutron sources are being developed in the world. Mercury is used as a target material to produce neutrons via the spallation reaction induced by injected protons. At the moment of the proton injection, the mercury vessel with a double wall structure is impulsively excited by the interaction between mercury and solid wall. The vibrational signals were measured in noncontact and remotely by using a Laser Doppler Vibrometer (LDV) system to evaluate the structure integrity. The extreme damages were assumed as the first step, i.e., the inner structure was partly broken by erosion. The dependency of vibrational behaviors on the damage was systematically investigated through numerical simulations and experiments. A LDV was installed to monitor the dependency of an electro-Magnetic Impact Testing Machine (MIMTM) vibration on the damage size. Through the numerical simulation, it was found that the target vessel vibration depends on the damage size. A technique referred to a Wavelet Differential Analysis (WDA) has been developed to enhance the effect of damages on the impulsive vibration behavior. However, the vibration signals obtained from MIMTM contain considerable noise. In order to reduce the noise effect on the impulsive vibration behavior, the statistical methods referred to an Analysis of Variance (ANOVA) and an Analysis of Covariance (ANCOVA) was applied. Numerical simulation results that obtained from controlling the damage size, were firstly added to random noise with various levels manually, and then were analyzed by the statistic methods. Then, the field data that measured from the real mercury target was analyzed. The results represent that the combination of WDA and ANOVA/ANCOVA could effectively indicate the damage dependency.
Naoe, Takashi; Kogawa, Hiroyuki; Wakui, Takashi; Haga, Katsuhiro; Teshigawara, Makoto; Kinoshita, Hidetaka; Takada, Hiroshi; Futakawa, Masatoshi
Journal of Nuclear Materials, 468, p.313 - 320, 2016/01
Mercury target vessel in the JSNS, which is made of 316L SS, is damaged owing to the pressure wave-induced cavitation resulting from the proton beam bombardment. The cavitation damage decreases the structural integrity of the target vessel and is currently a dominant factor to decide the service life in compared with the radiation damage. Injecting microbubbles into mercury is one of the prospective techniques to mitigate the pressure waves and cavitation damage. In the JSNS, a microbubble generator with a gas circulation system was installed and has been operated since October 2012. The effects of microbubble injection into mercury on pressure wave mitigation were studied using a laser Doppler vibrometer. The result showed that the vibrational velocity of the target vessel is clearly reduced according to the increase of void fraction. An average peak vibrational velocity under 340 kW operation with the void fraction of 0.1% was reduced to 1/4 of that without injecting microbubbles.
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.
Kogawa, Hiroyuki; Naoe, Takashi; Kyoto, Harumichi*; Haga, Katsuhiro; Kinoshita, Hidetaka; Futakawa, Masatoshi
Journal of Nuclear Science and Technology, 52(12), p.1461 - 1469, 2015/12Patent publication (In Japanese)
MW-class mercury target for the spallation neutron source is subjected to the pressure waves. Propagation of the pressure wave causes negative pressure which causes cavitation erosion and degrades the vessel. Microbubbles injection into mercury is an effective technique to suppress the pressure waves and cavitation erosion. The bubble-generator utilizing swirl flow of liquid (swirl-type bubble-generator) is suitable for a mercury target system. However, when the single generator was used, swirl flow remains at downstream. The remaining swirl flow causes the coalescence of bubbles which results in ineffective suppression of pressure waves. To solve this concern, a multi swirl-type bubble-generator, which consists of several single generators arraying in the plane perpendicular to mercury flow direction, was invented. The multi swirl-type bubble-generator generated the microbubbles with the sufficient size to suppress the pressure waves.
Futakawa, Masatoshi; Naoe, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro; Okita, Kohei*
Experimental Thermal and Fluid Science, 57, p.365 - 370, 2014/09
A liquid mercury target system for a megawatt-class spallation neutron source is being developed in the world. Proton beam is injected to the mercury target to induce spallation reaction. The moment the proton beams bombard the target, pressure waves are generated in the mercury by the thermally shocked heat deposition. The pressure waves excite the mercury target vessel and negative pressure that may cause cavitation along the vessel wall. Gas-bubbles will be injected into the flowing mercury to mitigate the pressure waves and suppress the cavitation inception. The injected gas-bubbles conditions were examined and the effects were predicted experimentally and theoretically from the viewpoints of macroscopic time-scale and microscopic time-scale, i.e. in the former is dominant the interaction between the structural vibration and the pressure in mercury, and in the later is essential the pressure wave propagation process.
Naoe, Takashi; Teshigawara, Makoto; Wakui, Takashi; Kinoshita, Hidetaka; Kogawa, Hiroyuki; Haga, Katsuhiro; Futakawa, Masatoshi
Journal of Nuclear Materials, 450(1-3), p.123 - 129, 2014/07
A JSNS mercury target vessel composed of type 316L stainless steel suffers radiation damage in the proton and neutron environment. In addition to this damage, the inner wall of the target vessel in contact with mercury is damaged as a result of the cavitation. The target vessel was replaced with a new target in November 2011, because the pneumatic bellows were damaged during the earthquake. Before replacing the target, disk specimens were cut from the beam window of the target vessel in order to investigate the cavitation damage inside the target vessel and to evaluate the change in the mechanical properties due to radiation damage. As a result, it was confirmed that flow-induced erosion damage was not observed on the flow guide. The cavitation damage was concentrated at the center and around both sides approximately 15 mm from the center of the beam window. Based on the detailed measurements, it was concluded that the eroded damage depth of the beam window was 250 m.
Takada, Hiroshi; Haga, Katsuhiro; Meigo, Shinichiro; Tatsumoto, Hideki; Kasugai, Yoshimi; Futakawa, Masatoshi
Proceedings of 11th International Topical Meeting on Nuclear Applications of Accelerators (AccApp '13), p.154 - 158, 2014/05
Remarkable progresses were achieved at a pulsed spallation neutron source in J-PARC. One is to mitigate high-pressure waves which are generated in a mercury target and a source of serious damage on the wall of target vessel by injecting gas micro-bubbles into mercury. It was confirmed with a novel in-situ diagnostic system using a laser Doppler vibrometer that the pressure waves were certainly attenuated with the gas micro-bubbles. Secondly, the supercritical cryogenic hydrogen system has been improved to remove impurity remained in the helium circulation loop by installing a purification system. As a result, the pressure drop at the heat exchanger was suppressed successfully down to several kPa even after operating for 95 days. Furthermore, we have succeeded in sampling hydrogen gas from the cryogenic hydrogen loop during operation and verified with a Raman spectroscopy that the para-hydrogen fraction was 100%, proving the neutronic performance at the moderator is kept unchanged.
Shiki, 19, P. 4, 2013/06
In the neutron source facility of J-PARC, protecting the structural integrity of the mercury target against the pressure wave attack which is generated by the injection of the high power proton beam is the most important issue to achieve the world strongest neutron beam. Previous off-line studies have shown that the impact force of pressure waves can be reduced using the cushioning effect of dispersed He micro-bubbles whose sizes are several hundred microns. Then, we developed swirl-type bubbler which can generate micro-bubbles in mercury, and fabricated the mercury target with the bubbler mouted in it. Also, by utilizing the advanced technique of micro machinning, we developed the reflective mirror and mouted it on the mercury target, which enabled the monitoring of target vibration by laser beam. As a result, the pressure wave mitigation effect by micro-bubbles injection was demonstrated in the operating mercury target for the first time in the world, and the 300 kW beam operation and the world strongest neutron beam generation were attained.
Kinoshita, Hidetaka; Kaminaga, Masanori; Haga, Katsuhiro; Terada, Atsuhiko; Hino, Ryutaro
Journal of Nuclear Science and Technology, 50(4), p.400 - 408, 2013/04
In the design of MW-class spallation target system using mercury to produce a practical neutron applications, keeping the highest level of safety is vitally important. To establish the safety of spallation target system, it is essential to understand the thermal-hydraulic properties of mercury. Through thermal-hydraulic experiments using a mercury experimental loop, which flows 1.2 m/h maximum, the following facts were experimentally confirmed. The wall friction factor was relatively larger than the Blasius correlation due to the effects of wall roughness. The heat transfer coefficients agreed well with the Subbotin correlation. Furthermore, for validation of the design analysis code, thermal hydraulic analyses were conducted by using the STAR-CD code under the same conditions as the experiments. Analytical results showed good agreements with the experimental results, using optimized turbulent Prandtl number and mesh size.
Kinoshita, Hidetaka; Wakui, Takashi; Matsui, Hiroki; Maekawa, Fujio; Kasugai, Yoshimi; Haga, Katsuhiro; Teshigawara, Makoto; Meigo, Shinichiro; Seki, Masakazu; Sakamoto, Shinichi; et al.
JAEA-Technology 2011-040, 154 Pages, 2012/03
In the MLF, relatively high level irradiated components will be generated. Therefore, these components can not be kept in standard facilities. For the irradiated components at the MLF, the storage plan using the facilities in the Nuclear Science Research Institute has been studied, but the concrete plan is not decided yet. In this report, outline of the components, prehistory of the studying for storage, schedule of the component generation and status of the possible facility, which is a hot laboratory, are described. Resulting from the comparison between the generation schedule and the plan of the hot laboratory, the difference is very large. Present status of the hot laboratory and the cost estimation of the modification to use for storage of the MLF components were studied. Using the hot laboratory seems not to have advantage from the view point of cost and modification method. Therefore, the study on a new storage facility construction will be started as soon as possible.
Sakai, Kenji; Sakamoto, Shinichi; Kinoshita, Hidetaka; Seki, Masakazu; Haga, Katsuhiro; Kogawa, Hiroyuki; Wakui, Takashi; Naoe, Takashi; Kasugai, Yoshimi; Tatsumoto, Hideki; et al.
JAEA-Technology 2011-039, 121 Pages, 2012/03
This report investigates the behavior, damage and restoration of a neutron source station of the MLF at the Great East Japan Earthquake and verified the safety design for emergency accidents in the neutron source station. In the MLF, after an occurrence of the Earthquake, strong quakes were detected at the instruments, the external power supply was lost, all of the circulators shut down automatically, and the hydrogen gas was released. The leakages of mercury, hydrogen and radio-activation gases did not occur. While, the quakes made gaps between the shield blocks and ruptured external pipe lines by subsidence around the building. But significant damages to the components were not found though the pressure drop of compressed air lines influenced on a target trolley lock system and so on. These results substantiated the validity of the safety design for emergency accidents in the source station, and suggested several points of improvement.
Haga, Katsuhiro; Kogawa, Hiroyuki; Wakui, Takashi; Naoe, Takashi; Futakawa, Masatoshi
Proceedings of 20th Meeting of the International Collaboration on Advanced Neutron Sources (ICANS-20) (USB Flash Drive), 6 Pages, 2012/03
Cavitation damage caused by the pressure wave in mercury is the crucial issue for the high power mercury target. Microbubble injection into mercury is the technology to mitigate the pressure wave, and the techniques to generate microbubbles in mercury flow, and to achieve the proper distribution of microbubbles have been investigated. We developed the swirl type bubbler which can generate the microbubbles efficiently. We performed mercury flow experiments using the target mockup model. We found that the proper size of microbubbles were distributed in the target, but the void fraction was less than 10 at the bottom area, which was lower than an expected value. In order to increase the void fraction, we changed the design of the mercury flow channel, moving the bubbler position forward near the beam window. With the help of the swirl flow, the homogeneity of microbubbles distribution at the beam window will be improved and the void fraction at the bottom area will be increased.