Cavitation damage prediction in mercury target for pulsed spallation neutron source using Monte Carlo simulation

Wakui, Takashi; Takagishi, Yoichi*; Futakawa, Masatoshi

Materials, 16(17), p.5830_1 - 5830_16, 2023/09

https://doi.org/10.3390/ma16175830

Cavitation damage on the mercury target vessel is induced by proton beam injection in mercury. The prediction method of the cavitation damage using Monte Carlo simulations was proposed taking into account of the uncertainties of the position of cavitation bubbles and impact pressure distributions. The distribution of impact pressure attributed to individual cavitation bubble collapsing was assumed to be the Gaussian distribution, and the probability distribution of the maximum value of impact pressures was assumed to be three kinds of distributions; the delta function, the Gaussian and Weibull distributions. Two parameters were estimated using Bayesian optimization by comparing the distribution of the cavitation damage obtained from experiment with that of accumulated plastic strain obtained from the simulation. It was found that the results obtained using the Weibull distribution reproduced the actual cavitation erosion phenomenon better than the other results.

Technical note for the cavitation damage inspection for interior surface of the mercury target vessel, 1; Development of specimen cutting machine for remote handling

Naoe, Takashi; Kinoshita, Hidetaka; Wakui, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro

JAEA-Technology 2022-018, 43 Pages, 2022/08

JAEA-Technology-2022-018.pdf:7.84MB

In the liquid mercury target system for the pulsed spallation neutron source of Materials and Life science experimental Facility (MLF) at the Japan in the Japan Proton Accelerator Research Complex (J-PARC), cavitation that is generated by the high-energy proton beam-induced pressure waves, resulting severe erosion damage on the interior surface of the mercury target vessel. The erosion damage is increased with increasing the proton beam power, and has the possibility to cause the leakage of mercury by the penetrated damage and/or the fatigue failure originated from erosion pits during operation. To achieve the long term stable operation under high-power proton beam, the mitigation technologies for cavitation erosion consisting of surface modification on the vessel interior surface, helium gas microbubble injection, double-walled beam window structure has been applied. The damage on interior surface of the vessel is never observed during the beam operation. Therefore, after the target operation term ends, we have cut out specimen from the target nose of the target vessel to inspect damaged surface in detail for verification of the cavitation damage mitigation technologies and lifetime estimation. We have developed the techniques of specimen cutting out by remote handling under high-radiation environment. Cutting method was gradually updated based on experience in actual cutting for the used target vessel. In this report, techniques of specimen cutting out for the beam entrance portion of the target vessel in high-radiation environment and overview of the results of specimen cutting from actual target vessels are described.

Progress of target system operation at the pulsed spallation neutron source in J-PARC

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.

Micro-impact damage caused by mercury bubble collapse

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.

Estimation of pitting damage induced by cavitation impacts

Soyama, Hitoshi*; Futakawa, Masatoshi; Homma, Kana*

Journal of Nuclear Materials, 343(1-3), p.116 - 122, 2005/08

https://doi.org/10.1016/j.jnucmat.2004.11.016

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.

Estimation of incubation time of cavitation erosion for various cavitating conditions

Soyama, Hitoshi*; Futakawa, Masatoshi

Tribology Letters, 17(1), p.27 - 30, 2004/07

https://doi.org/10.1023/B:TRIL.0000017415.79517.8c

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.

Off-line tests on pitting damage in mercury target

Futakawa, Masatoshi; Kogawa, Hiroyuki; Tsai, C.-C.*; Ishikura, Shuichi*; Ikeda, Yujiro

JAERI-Research 2003-005, 70 Pages, 2003/03

JAERI-Research-2003-005.pdf:12.08MB

A liquid-mercury target system for the MW-scale target is being developed in the world. The moment the proton beams bombard the target, stress waves will be imposed on the beam window and pressure waves will be generated in the mercury by the thermally shocked heat deposition. Provided that the negative pressure generates through its propagation in the mercury target and causes cavitation in the mercury, there is the possibility for the cavitation bubbles collapse to form pits on the interface between the mercury and the target vessel wall. In order to estimate the cavitation erosion damage due to pitting, two types of off-line tests were performed: Split Hopkinson Pressure Bar (SHPB), and Magnetic IMpact Testing Machine (MIMTM). The data on the pitting damage at the high cycle impacts up to 10 million were given by the MIMTM. As a result, it is confirmed that the mean depth erosion is predictable using a homologous line in the steady state with mass loss independently of testing machines and the incubation period is very dependent on materials and imposed pressures.

Effect of inner wall craking on the mercury flow induced vibration

Maeno, Koki*; Ariyoshi, Gen; Tsutsui, Kihei*; Saruta, Koichi; Kogawa, Hiroyuki; Li, Y.*; Futakawa, Masatoshi

no journal, , 

Cavitation damage is one of the issues for the mercury spallation target, which threatens the structural integrities of the target vessel wall. To reduce such cavitation damages, Japan Atomic Energy Agency (JAEA) tried to prevent the cavitation bubble growth using the "flow effect". To arrange the environment for the use of the "flow effect", a narrow channel was newly installed by adding an inner wall to the mercury target head. Moreover, the microbubble injection technique to the mercury was also used to reduce the pressure waves which is one of the causes of the cavitation bubble formation. Consequently, the damage could be almost weakened. However, the damage on the inner wall can still be accumulated gradually during the practical target operation. Then, the inner wall might be penetrated by such damage accumulation: wall cracking might happen to the inner wall. Therefore, development of a diagnostic technology for such inner wall cracking should be important. So, the purpose of this study is to clarify the flow field in the target head with wall cracking conditions. Effect of the wall cracking on the flow field in the target head was investigated by CFD analysis. For simplicity, the flow channel near the target head was simulated as two-dimensional models. As the results, the continuous vortices shedding was recognized in the cases of any cracking conditions. And, pulsation flows in the narrow channel were observed in the cases of the cracking width larger than 4 mm.

Effect of inner wall penetration on the flow field in double-walled structure channel

Maeno, Koki*; Ariyoshi, Gen; Saruta, Koichi; Murata, Atsushi*; Kogawa, Hiroyuki; Li, Y.*; Tsutsui, Kihei*; Futakawa, Masatoshi

no journal, , 

no abstracts in English