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Iwamoto, Yosuke; Yoshida, Makoto*; Matsuda, Hiroki; Meigo, Shinichiro; Satoh, Daiki; Yashima, Hiroshi*; Yabuuchi, Atsushi*; Kinomura, Atsushi*; Shima, Tatsushi*
JPS Conference Proceedings (Internet), 28, p.061003_1 - 061003_5, 2020/02
To predict the lifetime of target materials in high-energy radiation environments at spallation neutron sources, radiation transport codes such as PHITS are used to calculate the displacements per atom (DPA) value. In this work, to validate calculated DPA values of tungsten, we implemented 0.25-mm-diameter wire sample of tungsten in a proton irradiation device with a Gifford-McMahon cryocooler and measured the defect-induced electrical resistivity changes related to the displacement cross section using 389-MeV protons at 10 K. In comparison with experimental data under 1.1 and 1.9 GeV proton irradiation, we found that damage rate of tungsten increases with proton energy due to increase the number of secondary particle s produced by nuclear reactions.
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; Harjo, S.; Kawasaki, Takuro; Xiong, Z.*; Futakawa, Masatoshi
JPS Conference Proceedings (Internet), 28, p.061009_1 - 061009_6, 2020/02
At the J-PARC, a mercury target vessel made of 316L SS suffers proton and neutron radiation environment. The target vessel also suffers cyclic impact stress caused by the proton beam-induced pressure waves. The vessel suffers higher than 4.5
10
cyclic loading during the expected service life of 5000 h. We have investigated fatigue strength 316L SS up to gigacycle in the previous studies. The cyclic hardening and softening behavior were observed. In this study, to evaluate the cyclic hardening/softening behavior, the dislocation densities of specimens were measured using the neutron diffraction method at the MLF BL-19. The result showed that the dislocation density of a 316L SS was increased with increasing the number of loading cycles. By contrast, in the case of cold-rolled 316L SS, annihilation and re-accumulation of dislocation by cyclic loading were observed. In the workshop, result of neutron diffraction measurement will be introduced with the progress of fatigue test.
Meigo, Shinichiro; Matsuda, Hiroki; Iwamoto, Yosuke; Yoshida, Makoto*; Hasegawa, Shoichi; Maekawa, Fujio; Iwamoto, Hiroki; Nakamoto, Tatsushi*; Ishida, Taku*; Makimura, Shunsuke*
JPS Conference Proceedings (Internet), 28, p.061004_1 - 061004_6, 2020/02
no abstracts in English
Takada, Hiroshi; Haga, Katsuhiro
JPS Conference Proceedings (Internet), 28, p.081003_1 - 081003_7, 2020/02
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.
Saito, Shigeru; Okubo, Nariaki; Obayashi, Hironari; Wan, T.; Sugawara, Takanori; Sasa, Toshinobu; Maekawa, Fujio
JPS Conference Proceedings (Internet), 28, p.071003_1 - 071003_6, 2020/02
Japan Atomic Energy Agency (JAEA) proposes transmutation of minor actinides (MA) by accelerator-driven systems (ADS). The ADS designed by JAEA is a system composed by LBE (Lead-Bismuth Eutectic) spallation target and a subcritical core. In the ADS, a beam window (BW) is exposed in complex field of heavy irradiation by proton/neutron and corrosion by flowing LBE. To develop ADS structural materials, it is of critical importance to investigate materials used in such environment. Thus, JAEA plans to construct a proton irradiation facility at the J-PARC to prepare an irradiation database for candidate ADS structural materials and to investigate irradiation effects in flowing LBE environment. In this paper, giving a whole scope of the JAEA ADS development, some results of experimental measurements and the specific program for planed R&D will be presented.
Wakui, Takashi; Wakai, Eiichi; Kogawa, Hiroyuki; Naoe, Takashi; Hanano, Kohei; Haga, Katsuhiro; Takada, Hiroshi; Shimada, Tsubasa*; Kanomata, Kenichi*
JPS Conference Proceedings (Internet), 28, p.081002_1 - 081002_6, 2020/02
A mercury target vessel of J-PRAC is designed with a triple-walled structure consisting of the mercury vessel and a double-walled water shroud with internal and external vessels. During the beam operation at 500 kW in 2015, small water leakages from a water shroud of the mercury target vessel occurred twice. Design, fabrication and inspection processes were improved based on the lessons learned from the target failures. The total length of welding lines at the front of the mercury target vessel decreases drastically to approximately 55% by adopting monolithic structure cut out from a block of stainless steel by the wire-electrical discharge machining. Thorough testing of welds by radiographic testing and ultrasonic testing was conducted. The fabrication of the mercury target vessel #8 was finished on September 2017 and the beam operation using it started. Stable beam operation at 500 kW has been achieved and it could experience the maximum beam power of 1 MW during a beam test.
Ohdaira, Naoya; Saito, Shigeru; Wan, T.; Obayashi, Hironari; Sasa, Toshinobu
no journal, ,
J-PARC plans to install a lead-bismuth eutectic (LBE) spallation target to study the irradiation effects of structural materials in flowing LBE environment. A freeze seal valve is to be used for the LBE circulation system. LBE is known as a material which expands after solidification; hence the solidified LBE in freeze seal part will be deformed and tube in freeze seal part might be broken by the imposed stress consequently. To minimize the stress at freeze seal valve, deformation of stainless steel (SS) generated by LBE expansion in different cooling conditions were studied. It was found that annealing at a certain temperature for 24 hours is effective to reduce the stress.
Okubo, Nariaki; Fujimura, Yuki; Kitamura, Akane; Okuno, Yasuki
no journal, ,
Japan atomic energy agency has been conducting research activities for developing the accelerator driven system (ADS), which is expected to reduce and transmute radioactive wastes involved in spent fuels by nuclear power plants. The ADS adopts a liquid metal of lead-bismuth eutectic (LBE) as a coolant and also spallation target to produce high energy neutrons. In this study, effect of irradiation on corrosion behavior was evaluated for 316L stainless steel and T91 ferritic martensitic steel, which are candidate materials of ADS target window, through the immersion test under LBE with saturated and low oxygen concentration followed by ion irradiation experiment. In the case of soaking in LBE with saturated oxygen concentration for SS316L steels at 450
C, 330 hrs, non-irradiated region did not show clear oxide layer, however, irradiated region showed bi-layers of magnetite and spinel type oxides. The formation rate of oxide layer for irradiated region, 26 m/year, was about twice faster than that of non-irradiated region, 12 m/year. This result suggests that diffusion behavior after irradiation and mass transfer in the interface between LBE and steel surface is important for understanding of irradiation effect on liquid metal corrosion.
Suzudo, Tomoaki
no journal, ,
Although tungsten attracts attention as candidates for plasma facing materials in nuclear fusion reactors, hydrogen radioactive isotopes in plasma may be captured by irradiation defects in this material, leading to a serious problem. Therefore, it is important to suppress irradiation defect accumulation in tungsten materials, and a possible solution is to add alloy elements that suppress the defects. For this reason, we searched for optimum alloying elements using first principles calculation and kinetic Monte Carlo method, and the result suggested that chromium and vanadium may be promising candidates.
Harada, Masahide; Takada, Hiroshi
no journal, ,
In the spallation neutron source at J-PARC, proton beam hits a mercury target. Above or below the target, there are three liquid hydrogen moderators. Around the target and moderator, beryllium and iron reflectors are located. These components with helium atmosphere are set into the vessel which has a proton-beam windows. In the design stage, for a construction of maintenance and storage scenarios, DPA which is a major index of radiation damage were evaluated for each component with the PHITS code. And for mechanical designs of the target, the moderator and so on, nuclear heat was also estimated with the PHITS code. The PHITS code was recently updated recently. Therefore, the DPA calculation and the nuclear heat calculation were updated with the latest PHITS code. As results, it was confirmed that there was little significant difference between the latest estimated data and the old ones.
Nemoto, Hideyuki; Wakai, Eiichi; Kinoshita, Hidetaka; Masuda, Shiho; Harada, Masahide; Takada, Hiroshi; Ishikawa, Koji*; Imanari, Kei*; Ito, Takeshi*
no journal, ,
no abstracts in English
