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Naoe, Takashi; Hasegawa, Shoichi; Ahmed, B.*; Futakawa, Masatoshi
no journal, ,
Cavitation damage, which is induced by pressure waves in mercury, is viewed as one of the critical issues to satisfy high power spallation neutron source. Microbubble injection into the mercury is under study to improve mitigation of the pressure waves. In general, microbubble dissolves in liquid swiftly, therefore, it is important to estimate its lifetime to determine the injection position and bubble distribution. However, data for the lifetime estimation in mercury are insufficient. In this study, since mercury is an opaque liquid, helium microbubbles in contact with an acrylic wall were observed and their lifetimes were measured. Based on the observed bubbles, actual lifetime of bubbles suspended in the liquid was estimated. It was found that lifetime of microbubbles in mercury is longer than in water.
Aihara, Jun; Ueta, Shohei; Yasuda, Atsushi; Ishibashi, Hideharu; Sawa, Kazuhiro; Motohashi, Yoshinobu*
no journal, ,
Japan Atomic Energy Agency (JAEA) has started to study and develop ZrC coated fuel particles for advanced high temperature gas cooled reactors. The ZrC coating layers were fabricated with bromide process at JAEA. We report in this study the microstructures of the ZrC coating layers deposited in the second year of the project. We already reported the microstructure of the one deposited in the first year of the project last year. The ZrC coating layer deposited at lower temperatures contains less free carbons. The crystal grains of ZrC were columner in shape and oriented in the region containing less free carbons. The orientation was different from the one reported in the last year. In addition to the stoichiometry of the ZrC layer, the microstructure of PyC/ZrC boundary also depended on the deposition temperature. The fibrous carbon structure is observed at PyC/ZrC boundary when the ZrC layer is deposited at higher temperature but not when ZrC layer is deposited at lower temperature.
Yamaguchi, Yoshihito*; Kogawa, Hiroyuki; Naoe, Takashi; Futakawa, Masatoshi
no journal, ,
High power spallation targets for neutron sources are being developed in the world. A mercury target is being installed in the material and life science facility of J-PARC (Japan Proton Accelerator Research Complex). The mercury target is subjected to pressure waves caused by a proton beam bombardment. The pressure waves load macroscopic stresses on the target vessel and induce the cavitaion in mercury through the pressure wave propagation processes. When cavitation bubbles collapse, the localized impact damages so-called pitting damage, occur on the target vessel. The target vessel is subjected to the pitting damage and macroscopic stress at the same time. It is necessary, therefore, to evaluate the superimposed effect of macroscopic stresses the pitting damage. Pitting damage tests were carried out using a ultrasonic cavitation testing with a static tensile-stress loading unit. The results showed that the damage increased with the imposed tensile stress.
Bucheeri, A.; Kogawa, Hiroyuki; Naoe, Takashi; Futakawa, Masatoshi; Maekawa, Katsuhiro*
no journal, ,
A high-power liquid mercury target system for spallation neutron source is being developed in Japan Atomic Energy Agency. Cavitation will be induced by pressure waves which are caused by high intense proton beam injection into mercury. Injection of microbubbles in mercury with 50 to 200
m in diameter may be effective to mitigate the cavitation. The effectiveness is dependent on bubble size and population. To investigate the behavior of bubble formation in mercury from a nozzle and develop microbubbles injection technique, numerical simulation on bubble injection in stagnant and flowing mercury were carried out using a Computational Fluid Dynamics (CFD) code. The simulation in stagnant showed that bubble grew around the outer wall of the nozzle. Bubble computed under flowing condition was smaller than that in stagnant due to the drag and shearing fources induced by mercury flow.
Osone, Ryuji; Bucheeri, A.; Kurishita, Hiroaki*; Kato, Masahiro*; Yamasaki, Kazuhiko*; Maekawa, Katsuhiro*; Naoe, Takashi; Futakawa, Masatoshi
no journal, ,
Liquid mercury target system for high power spallation neutron sources is being developed. When high intensity proton beams are injected into the target, pressure waves are generated by the thermal shock in mercury and pitting damage will be imposed on the target vessel. Bubble injection into mercury is effective to mitigate the pressure waves. In this work, we propose a method of fabricating meso-nozzle for bubble injection. The method is based on powder metallurgy by inserting thin glass fibers into a metal powder matrix to create a green compact, followed by sintering at a temperature between the melting points of the powder and the fiber. SUS316L and molybdenum powders were used as the nozzle matrix materials. In order to investigate optimum sintering condition, experiments were performed at different combination of pressing load and sintering temperature. We found that in molybdenum high relative density and straight hole with circlar cross section were obtained.
Nemoto, Hiroyuki*; Shiina, Yasuaki; Inagaki, Terumi*; Ogi, Hiromichi*
no journal, ,
no abstracts in English