Recent status of the pulsed spallation neutron source at J-PARC

Takada, Hiroshi; Haga, Katsuhiro

JPS Conference Proceedings (Internet), 28, p.081003_1 - 081003_7, 2020/02

https://doi.org/10.7566/JPSCP.28.081003

At the Japan Proton Accelerator Research Complex (J-PARC), the pulsed spallation neutron source has been in operation with a redesigned mercury target vessel from October 2017 to July 2018, during which the operational beam power was restored to 500 kW and the operation with a 1-MW equivalent beam was demonstrated for one hour. The target vessel includes a gas-micro-bubbles injector and a 2-mm-wide narrow mercury flow channel at the front end as measures to suppress the cavitation damage. After the operating period, it was observed that the cavitation damage at the 3-mm-thick front end of the target vessel could be suppressed less than 17.5 m.

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.

Failure probability analysis on mercury target vessel

Ishikura, Shuichi*; Shiga, Akio*; Futakawa, Masatoshi; Kogawa, Hiroyuki; Sato, Hiroshi; Haga, Katsuhiro; Ikeda, Yujiro

JAERI-Tech 2005-026, 65 Pages, 2005/03

JAERI-Tech-2005-026.pdf:2.86MB

Failure probability analysis was carried out to estimate the lifetime of the mercury target which will be installed into the JSNS (Japan spallation neutron source) in J-PARC (Japan Proton Accelerator Research Complex). The lifetime was estimated as taking loading condition and materials degradation into account. Considered loads imposed on the target vessel were the static stresses due to thermal expansion and static pre-pressure on He-gas and mercury and the dynamic stresses due to the thermally shocked pressure waves generated repeatedly at 25 Hz. Materials used in target vessel will be degraded by the fatigue, neutron and proton irradiation, mercury immersion and pitting damages, etc. The imposed stresses were evaluated through static and dynamic structural analyses. The material-degradations were deduced based on published experimental data. As results, it was quantitatively confirmed that the failure probability for the lifetime expected in the design is very much lower, 10 in the safety hull, meaning that it will be hardly failed during the design lifetime. On the other hand, the beam window of mercury vessel suffered with high-pressure waves exhibits the failure probability of 12%. It was concluded, therefore, that the leaked mercury from the failed area at the beam window is adequately kept in the space between the safety hull and the mercury vessel to detect mercury-leakage sensors.

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.

Current status of pulsed spallation neutron source at J-PARC

Takada, Hiroshi

no journal, , 

At the Japan Proton Accelerator Research Complex, a pulsed spallation neutron source provides neutrons with high-intensity and narrow pulse width to promote a variety field of materials science by injecting high power proton beam of 3-GeV, 1 MW at repetition rate of 25 Hz. The core components of the spallation neutron source are a mercury target, liquid hydrogen moderators and a reflector with beryllium and iron. Their sizes and arrangement were optimized to get superior neutronics performance for 100% para-hydrogen as the moderator material. Since the lifetime of the mercury target vessel made from SS316L steel is determined by the pitting damage induced by the pressure wave generated at the pulsed proton beam injection, mitigating the pitting damage is the most critical issue to achieve 1 MW operation for long time. So far, gas micro-bubbles injection technique and a target front structure to get faster mercury flow in narrow channel were employed for mitigating the pitting damage in the mercury target vessel. A pitting damage of 25 m was observed on the target front after 670 MWh operation with an average power of 406 kW. In 2018, it is planned to observe the target front of the newly manufactured target after operation with a power of 300 to 500 kW. Further developments of the narrow channel structure of the target front will be carried out. It is also planned to make post irradiation examination to study radiation damage of the target vessel in other facility of Japan Atomic Energy Agency.