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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.
Takada, Shoji; Takizuka, Takakazu; Kunitomi, Kazuhiko; Yan, X.
Nihon Kikai Gakkai Dai-9-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu, No.04-2, p.273 - 276, 2004/06
Design and evaluation method to reduce blade tip clearance to around 1 mm, which is around 30% lower than that of the same power industrial air compressor, was newly developed for the helium gas compressor of the GTHTR300 to enhance design efficiency. The method was verified in the aerodynamic performance test using a 1/3 scale, 4-stage helium gas compressor model. The blade tip clearance was numerically evaluated so that it should be around 0.4 mm in operation, and also measured during operation by using optical displacement sensor in the test. Aerodynamic performance tests were successfully carried out using the test model, which was connected with a helium gas loop. The inlet pressure was varied from 0.196 to 0.883 MPa. The measured efficiency was around 84 % at the design pressure ratio and the rated rotational speed of 10800 rpm, which prospected that the helium gas compressor of the GTHTR300 can be operated with efficiency over 90 % by extrapolation. The present study is entrusted from the Ministry of Education, Culture, Sports, Science and Technology of Japan.