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Naoe, Takashi; Xiong, Z.*; Futakawa, Masatoshi
Journal of Nuclear Materials, 506, p.12 - 18, 2018/08
Times Cited Count：8 Percentile：58.71(Materials Science, Multidisciplinary)A mercury target for neutron source (made of 316L SS) suffers not only proton and neutron radiation damage, but also cyclic impact stress caused by pressure waves. In the previous study, we carried out an ultrasonic fatigue test to investigate the gigacycle fatigue strength of 316L SS, concluding that specimen surface temperature rose abruptly more than 300
C just before failure. In this study, to clarify the mechanism of the temperature rise, we measured temperature distribution with a thermography during the fatigue test. The experimental results showed that the temperature rose locally only at the crack tip and the peak position moved with the crack propagation. We also carried out a nonlinear structural analysis by LS-DYNA to estimate the temperature rise with strain energy of elements. The analytical result showed that the heat due to plastic deformation at the crack tip is dominant for the temperature rise rather than the friction between crack surface.
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
Times Cited Count：6 Percentile：48.59(Materials Science, Multidisciplinary)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.
Wakui, Takashi; Wakai, Eiichi; Naoe, Takashi; Shintaku, Yohei*; Li, T.*; Murakami, Kazuya*; Kanomata, Kenichi*; Kogawa, Hiroyuki; Haga, Katsuhiro; Takada, Hiroshi; et al.
Journal of Nuclear Materials, 506, p.3 - 11, 2018/08
Times Cited Count：4 Percentile：34.86(Materials Science, Multidisciplinary)The mercury target vessel is designed as multi-walled structure with thin wall (min. 3 mm), and assembled by welding. In order to estimate the structural integrity of the vessel, it is important to measure the defects in welding accurately. For nondestructive tests of the welding, radiographic testing is applicable but it is difficult to detect for some defect shapes. Therefore it is effective to do ultrasonic testing together with it. Because ultrasonic methods prescribed in JIS inspect on the plate with more than 6 mm in thickness, these methods couldn't be applied as the inspection on the vessel with thin walls. In order to develop effective method, we carried out measurements using some testing method on samples with small defect whose size is specified. In the case of the latest phased array method, measured value agreed with actual size. It was found that this method was applicable to detect defects in the thin-walled structure for which accurate inspection was difficult so far.
Haga, Katsuhiro; Kogawa, Hiroyuki; Wakui, Takashi; Naoe, Takashi; Wakai, Eiichi; Takada, Hiroshi
no journal, ,
At the Japan Spallation Neutron Source (JSNS), there was trouble twice at the water shroud of the mercury target due to the thermal stress during operating periods with proton beam power at 500 kW in 2015. The target vessel, made from 316L stainless steel, has a triple-walled structure consisting of mercury vessel, inner and outer water shrouds, where the interstitial space between the mercury vessel and the water shroud is filled with helium gas. For the first trouble, the leak was to the outside of the shroud and the location was specified at a welded portion around a bolt connection. For the second trouble, the leak was detected in the helium layer. Results of FEM simulations suggested that the location was susceptible to fatigue cracking due to the cyclic thermal stress induced by beam trips. The cause of the troubles was attributed to the complicated structural design in which incompleteness remained at welding. The next target vessel design was improved to reduce welding lines ca. 30% and bolt connection as much as possible.
Saito, Shigeru; Kikuchi, Kenji*; Suzuki, Kazuhiro; Hatakeyama, Yuichi; Endo, Shinya; Suzuki, Miho; Okubo, Nariaki; Kondo, Keietsu
no journal, ,
The world's first megawatt-class lead-bismuth target, MEGAPIE (MEGAwatt Pilot Experiment), was dismantled and post irradiation examination (PIE) samples were prepared at PSI hot-lab. The samples were shipped to each institutions including JAEA. The samples were cut from the beam window (BW, T91) and the flow guide tube (FGT, SS316L). And all samples are prepared without LBE. The irradiation conditions of the specimens irradiated at SINQ target were as follows: proton energy was 580 MeV, irradiation temperatures were ranged from 251 to 341C, and displacement damage levels were ranged from 0.16 to 1.57 dpa. PIE including SP (small punch) and three point bending tests were performed. SP tests were executed for T91 and SS316L specimens at R.T. in air condition. Specimen size for SP test with 2.4 mm steel-ball is 8 mm 
8 mm 0.5 mm. T91 specimens were cut from the Spitze (triangle) sample and polished to thickness of 0.5 mm. The OM/SP specimens of SS316L were polished to thickness of 0.5 mm. Three point bending tests were executed for SS316L specimens at R.T. in air condition. The bend bar specimens of SS316L without notch were employed. Results of the SP tests and three point bending tests on the irradiated specimens will be presented at the workshop. Cross sectional observation on the Spitze sample and microstructural observation by TEM will be also reported.
Wakui, Takashi; Naoe, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro; Wakai, Eiichi; Takada, Hiroshi; Futakawa, Masatoshi
no journal, ,
The mercury target vessel has large size as 1.31.32.5 m
. In view of reducing the amount of wastes, we have studied the structure so that the fore part could be separated. The flange is required to have high seal performance less than 110
Pam/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 of 973, 1173, 1373 and 1473 K 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.
