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Naoe, Takashi; Wakui, Takashi; Kinoshita, Hidetaka; Kogawa, Hiroyuki; Teshigawara, Makoto; Haga, Katsuhiro
JAEA-Technology 2023-022, 81 Pages, 2024/01
JAEA-Technology-2023-022.pdf:9.87MB
In the liquid mercury target system for the pulsed spallation neutron source of Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC), pressure waves that is generated by the high-energy proton beam injection simultaneously with the spallation reaction, resulting severe cavitation erosion damage on the interior surface of the mercury target vessel. Because the bubble of pressure wave-induced cavitation collapsing near the interior surface of the mercury target vessel with applying the large amplitude of localized impact on the surface. Since the wall thickness of the beam entrance portion of the target vessel is designed to be 3 mm to reduce thermal stress due to the internal heating, the erosion damage has the possibility to cause the vessel fatigue failure and mercury leakage originated from erosion pits during operation. To reduce the erosion damage by cavitation, a technique of gas microbubble injection into the mercury for pressure wave mitigation, and double-walled structure of the beam window of the target vessel has been applied. A specimen was cut from the beam window of the used mercury target vessel in order to investigate the effect of the damage mitigation technologies on the vessel, and to reflect the consideration of operation condition for the next target. We have observed cavitation damage on interior surface of the used mercury target vessel by cutting out the disk shape specimens. Damage morphology and depth of damaged surface were evaluated and correlation between the damage depth and operational condition was examined. The result showed that the erosion damage by cavitation is extremely reduced by injecting gas microbubbles and the damage not formed inside narrow channel of the double-walled structure for relatively high-power operated target vessels.
Kogawa, Hiroyuki; Futakawa, Masatoshi; Haga, Katsuhiro; Tsuzuki, Takayuki*; Murai, Tetsuro*
JAEA-Technology 2022-023, 128 Pages, 2022/11
JAEA-Technology-2022-023.pdf:9.0MB
In a mercury target of the J-PARC (Japan Proton Accelerator Research Complex), pulsed proton beams repeatedly bombard the flowing mercury which is confined in a stainless-steel vessel (target vessel). Cavitation damage caused by the propagation of the pressure waves is a factor of the life of the target vessel. As a measure to reduce damages, we developed a bubbler to inject the gas microbubbles into the flowing mercury, which can reduce the pressure waves. To operate the mercury target vessel stably with the 1 MW high-intensity proton beams, further reduction of the damage is required. The bubbler setting position should be closer to the beam window to increase the bubble population, which could enhance the reduction effect on the pressure waves and damage. However, the space at the beam window of the target vessel is restricted. The bubbler design and setting position as well as the vane design for the mercury flowing pattern are optimized by means of a machine learning technique to get more suitable bubble distribution, increasing in bubble population and optimizing bubble size nearby the beam window of the target vessel. The results of CFD analyses performed with 1000 cases were used for machine learning. Since the flow rate of mercury affects the temperature of the target vessel, this was used for the constraint condition. As a result, we found a design of mercury target vessel that can increase the bubble population by ca. 20% higher than the current design.
Haga, Katsuhiro
Kasokuki, 18(4), p.210 - 216, 2022/01
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
JAEA-Conf 2017-001, p.51 - 56, 2018/01
A pulsed spallation neutron source of Japan Proton Accelerator Research Complex (J-PARC) is aimed at promoting a variety of cutting-edge materials researches at state-of-the-art neutron instruments with neutrons generated by a 3-GeV proton beam with a power of 1-MW at a repetition rate of 25 Hz. In 2015, for the first time it received 1-MW equivalent proton beam pulse, and the beam power for user program was ramped up to 500 kW. The moderator system of the neutron source was optimized to use (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 degrees, (3) neutron absorber made from Ag-In-Cd alloy to make pulse widths narrower and pulse tails lower. As a result, it gives highest intensity pulsed neutrons per incident proton in the world. Towards the goal to achieve the target operation at 1-MW for 5000 h in a year, efforts to mitigate cavitation damages at the target vessel front with injecting gas micro-bubbles into the mercury target are under way. Also, improvement of structural target vessel design is an urgent issue since there was failure twice at the water shroud of the mercury target due to the thermal stress during operating periods at 500 kW in 2015.
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
Times Cited Count：11 Percentile：71.62(Materials Science, Multidisciplinary)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.
Futakawa, Masatoshi; Naoe, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro; Okita, Kohei*
Experimental Thermal and Fluid Science, 57, p.365 - 370, 2014/09
Times Cited Count：10 Percentile：46.63(Thermodynamics)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.
Ida, Masato
Nihon Ryutai Rikigakkai Nenkai 2005 Koen Rombunshu (CD-ROM), 6 Pages, 2005/09
The resonance frequencies and oscillation phases of three acoustically coupled bubbles in a fluid are examined to show that avoided crossings can appear in a few-bubble system. Using a simple coupled oscillator model, we show that if at least three bubbles exist, it is possible for their resonance frequencies as functions of the separation distances between the bubbles to experience an avoided crossing. Furthermore, by focusing our attention on the oscillation phases and the transition frequencies [Ida, Phys. Lett. A 297, 210 (2002); J. Phys. Soc. Jpn. 71, 1214 (2002)] of the coupled bubbles, we show that a distinct state exchange takes place between the bubbles at a point in the avoided crossing region, where a resonance frequency of the triple-bubble system crosses with a transition frequency not corresponding to the resonance frequencies.
Ida, Masato
Physics of Fluids, 17(9), p.097107_1 - 097107_13, 2005/09
Times Cited Count：16 Percentile：52.83(Mechanics)The transition frequencies of multibubble systems in a sound field are reexamined theoretically to confirm their existence and further clarify their physical properties. Via a forced coupled oscillator model, the following results are obtained: (1) further details of the characteristics of the transition frequencies, (2) the theoretical determination of the threshold distances for the appearance of the sub-transition frequencies, (3) a simple understanding of the sign reversal of the interaction force, and (4) the clarification of several similarities and differences among the natural, resonance, and transition frequencies in double-bubble cases. The present effort enforces our claim that transition frequencies causing no resonance response exist in multibubble systems and thoroughly clarifies the physical effects of the transition frequencies and their roles in the sign reversal of the interaction force.
Kogawa, Hiroyuki
Jikken Rikigaku, 5(1), P. 64, 2005/03
no abstracts in English
Futakawa, Masatoshi
Shindo Gijutsu, (10), p.22 - 26, 2004/11
no abstracts in English
Futakawa, Masatoshi; Naoe, Takashi*; Kogawa, Hiroyuki; Ishikura, Shuichi*; Date, Hidefumi*
Zairyo, 53(3), p.283 - 288, 2004/03
no abstracts in English
Ida, Mizuho*; Horiike, Hiroshi*; Akiba, Masato; Ezato, Koichiro; Iida, Toshiyuki*; Inoue, Shoji*; Miyamoto, Seiji*; Muroga, Takeo*; Nakamura, Hideo; Nakamura, Hiroshi*; et al.
Journal of Nuclear Materials, 307-311(Part2), p.1686 - 1690, 2002/12
Times Cited Count：6 Percentile：39.54(Materials Science, Multidisciplinary)no abstracts in English
Kogawa, Hiroyuki; Ishikura, Shuichi*; Futakawa, Masatoshi; Hino, Ryutaro
Jikken Rikigaku, 2(2), p.122 - 127, 2002/06
no abstracts in English
*; ; ; ; Fukami, Akihiro*; *; Igawa, Kenichi*
PNC TN9410 91-175, 52 Pages, 1991/05
An acoustic detection method is one of the FBR reactor core malfunction detection methods, and is regarded as being promising. In this study, the preliminary experiment of boiling detection by acoustic method was conducted at JOYO to measure the acoustic signal level and to investigate the applicability of the acoustic method. The experiment was performed on June 13 and 14, 1990 during the 8th periodic inspection of JOYO. The results obtained though the experiment are as follows: (1)Sodium bubbling (boiling) induced by the electric heater was detected as the fluctuation of temperature single of the thermocouple attached to surface of the electric heater. (2)Bubbling single of the acoustic detector could not be identified cleary because of the high background noise caused by the primary main pump vibration, sodium flow in the reacter vessel and the electric supply in the containment vessel. (3)The correlation between the signal of the acoustic detector or the fluctuation of temperature signal of the thermocouple and the flow rate of the primary loops was not ascertained. It became clear through this study that the validity of the reactor core malfunction detction by acoustic method depend on the peculiar noise level in the reactor vessel, and the reduction of noise is the subject for a future study.
Haga, Katsuhiro; Kogawa, Hiroyuki; Naoe, Takashi; Wakui, Takashi; Futakawa, Masatoshi; Takada, Hiroshi
no journal, ,
For the mercury target of a pulsed spallation neutron source of J-PARC, cavitation damage of the target vessel wall which is caused by the pressure wave in mercury induced by high power pulsed proton beam of 1 MW is the crucial issue. In order to mitigate the cavitation damage, a microbubble injection technique has been developed. A microbubble generator to generate bubbles with a diameter less than 100
m in mercury was developed and has been used in the mercury target system of J-PARC since October 2012. The effect of microbubble injection into mercury was verified by using a laser Doppler vibrometer (LDV). The measured data showed that the displacement velocity of the target vessel was reduced to 1/3 in average by injecting microbubbles. For further development of the high power target, we focused on the mercury flow effect to mitigate the cavitation damage. In order to realize this effect into the target design of J-PARC, we adopted doubled-walled structure to the beam window of the target vessel. The mercury flow channel with a narrow gap of 2 mm was made by adding an inner wall to just inside of the beam window. Numerical simulations were carried out using the conventional code, ANSYS FLUENT. While the mercury velocity outside of the narrow channel was 1.2 m/s, the mercury velocity in the narrow channel increased to almost 4 m/s, which was promising to suppress the cavitation damages.
Naoe, Takashi; Wan, T.; Kogawa, Hiroyuki; Futakawa, Masatoshi
no journal, ,
Pressure wave propagation and following cavitation bubble and liquid jet from free-surface were analyzed through the high-speed photography method to study the effect of gas wall on pressure wave mitigation in mercury target for J-PARC. Spark discharge system was used as the pressure wave generator in acrylic tube filled with water. Distance among the source of pressure, the wall, and free-surface were parametrically changed in order to investigate the effect of the boundary conditions on jet behaviors. It was found that the velocity of liquid jet is changed correlated with the both of distances from free surface and wall. Velocity of jet is sufficiently smaller than the velocity of microjet (100
200 m/s), which is emitted during the collapsing of cavitation bubble and is dominant factor to produce cavitation erosion. Therefore, it was suggested that the gas wall has the potential to reduce the cavitation damage of the mercury target.
Haga, Katsuhiro; Naoe, Takashi; Wakui, Takashi; Kogawa, Hiroyuki; Kinoshita, Hidetaka; Futakawa, Masatoshi
no journal, ,
For the mercury target of a pulsed spallation neutron source of J-PARC, cavitation damage of the target vessel wall which is caused by the pressure wave in mercury induced by high power pulsed proton beam of 1 MW is the crucial issue. So far, the analytical and experimental studies and the operational experiences of SNS suggest that the rapid mercury flow can mitigate the cavitation damages. In order to include this effect into the target design of J-PARC, we adopted doubled-walled structure to the beam window of the target vessel. The mercury flow channel with a narrow gap of 2 mm was made by adding an inner wall to just inside of the beam window. In order to investigate the mercury flow distribution and flow field, numerical simulations were carried out using the conventional code, ANSYS FLUENT. While the mercury velocity outside of the narrow channel was 1.2 m/s, the mercury velocity in the narrow channel increased to almost 4 m/s, which was promising to suppress the cavitation damages. The effect of the inner wall failure of the narrow channel on the mercury flow was also evaluated. The round hole was created on the inner wall at the center of the beam window. The simulation results and the water experimental results showed that the mercury flow velocity in the narrow channel was almost the same with the case without a hole if the hole diameter is around 10 mm.
Haga, Katsuhiro; Naoe, Takashi; Wakui, Takashi; Kogawa, Hiroyuki; Futakawa, Masatoshi; Kai, Tetsuya; Kinoshita, Hidetaka; Takada, Hiroshi
no journal, ,
The pressure waves are generated in the mercury target of J-PARC by the injection of high power pulsed proton beams and induce cavitation damages on the mercury target wall. The damages are the serious threat factor for the lifetime of the target vessel. After the beam operation of 200 kW corresponding to the accumulated power of 470 MWh, damages with the maximum depth of 0.25 mm were found on the inner surface of the mercury target, and the counter measure to mitigate the damage was recognized to be important. The technique to inject micro-bubbles into the mercury target vessel which has been developed to mitigate the cavitation damages was applied to the next target vessel and the beam operation in the range of 200 kW to 300 kW was continued to 2050 MWh. A specimen was cut out from the target vessel and inspected visually by a remote video camera. No conspicuous damages were found on the specimen. This fact demonstrates the efficacy of the micro-bubble injection to mitigate the cavitation damages. The newly installed target vessel has double wall structure at the beam window as the additional technique for the cavitation damage mitigation. The rapid mercury flow in the narrow channel made by the double wall prevent the cavitation bubble from growing and moderate the severity of the cavitation energy. The efficacy of the double wall structure will be investigated by cutting out the specimen from the target vessel in the future.
Ito, Kei; Ezure, Toshiki; Kunugi, Tomoaki*; Ohshima, Hiroyuki
no journal, ,
no abstracts in English
Ito, Kei; Ezure, Toshiki; Tanaka, Masaaki
no journal, ,
Related to the establishment of evaluation method of vortex cavitation, applicability of evaluation equation of pressure drop at vortex center based on the Burgers model has been investigated. Outline of modification of the vortex model in the evaluation equation and result of validation of the modified evaluation equation were reported.
