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Journal Articles

Assessments of crack length-water leak correlation on ITER vacuum vessel and inherent safety of Tokamak-type fusion machine

Nakahira, Masataka; Shibui, Masanao*

Nihon Kikai Gakkai Dai-9-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu, No.04-2, p.267 - 272, 2004/06

A small water leak can cause a plasma disruption in a tokamak-type fusion machine. This plasma disruption will induce electromagnetic (EM) force acting in the vacuum vessel that is a physical barrier of tritium and activated dust. If the VV can sustain an unstable fracture by the EM force, the structural safety will be assured and the inherent safety will be demonstrated. Therefore, a new analytical model to evaluate the through crack and leak rate of cooling water is proposed, with verification by experimental leak measurements. Based on the analysis, the critical crack length to terminate plasma in ITER is evaluated as about 2 mm. On the other hand, the critical crack length for unstable fracture is obtained as about 400 mm. It is concluded that EM forces induced by the small leak to terminate plasma will not cause unstable fracture of the VV; thus the inherent safety is demonstrated.

JAEA Reports

Development of fabrication technology for ITER vacuum vessel

Nakahira, Masataka; Shibanuma, Kiyoshi; Kajiura, Soji*; Shibui, Masanao*; Koizumi, Koichi; Takeda, Nobukazu; Kakudate, Satoshi; Taguchi, Ko*; Oka, Kiyoshi; Obara, Kenjiro; et al.

JAERI-Tech 2002-029, 27 Pages, 2002/03


The ITER vacuum vessel (VV) R&D has progressed with the international collaborative efforts by the Japan, Russia and US Parties during the Engineering Design Activities (EDA). Fabrication and testing of a full-scale VV sector model and a port extension have yielded critical information on the fabrication and assembly technologies of the vacuum vessel, magnitude of welding distortions, dimensional accuracy and achievable tolerances during sector fabrication and field assembly. In particular, the dimensional tolerances of $$pm$$3 mm for VV sector fabrication and $$pm$$10 mm for VV sector field assembly have been achieved and satisfied the requirements of $$pm$$5 mm and $$pm$$20 mm, respectively. Also, the basic feasibility of the remote welding robot has been demonstrated. This report presents detailed fabrication and assembly technologies such as welding technology applicable to the thick wall without large distortion, field joint welding technology between sectors and remote welding technology through the VV R&D project.

Oral presentation

Fatigue behavior on welded joint for JT-60SA vacuum vessel

Yanagi, Yutaka*; Shibui, Masanao*; Kanahara, Toshio*; Mochida, Tsutomu*; Ejiri, Mitsuru*; Asano, Shiro*; Shibama, Yusuke; Masaki, Kei; Sakasai, Akira

no journal, , 

JT-60SA Vacuum Vessel (VV) has D-shaped cross section and double-walled structure. It consists of the inner and outer wall reinforced by poloidal ribs and is made of SUS316L (Co$$<$$0.05wt%). The welding outer wall on rib (so called continuous plug) is performed from the outside of double-wall. Since it is difficult to confirm the penetration bead from the inside of double-wall, an incomplete penetration is assumed to be included in this welded joint. In this study, the fatigue test of continuous plug welded joint with an artificial incomplete penetration was performed to investigate the effect of the incomplete penetration on fatigue behavior and fatigue strength.

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