24th Symposium on Fusion Technology

11 - 15 September 2006 - Palace of Culture and Science, Warsaw, Poland

TOPIC: G - Vessel/Vessel-in Engineering and Remote Handling

STRUCTURAL AND FRACTURE MECHANICS ANALYSIS OF ITER VACUUM VESSEL (P2-G-273)

Masahide Iguchi, Masakatsu Saito Institute of Engineering Mechanics, University of Tsukuba Tennodai 1-1-1 305-8573 Tsukuba Japan

The ITER vacuum vessel (VV) is a double-wall torus and a safety component confining radioactive materials such as tritium and activated dust. The eddy currents are induced on VV by plasma centered disruption (CD). And the electromagnetic (EM) force induced by an interaction of the eddy currents and the magnetic fields is applied on VV in the direction of center of plasma. During ITER machine life time, the assumed number of CD is 3000 and VV must assure the safety operation of ITER. Hence a structural and a fatigue crack growth analysis are required. The purpose of this study is to confirm the structural integrity of VV by global 3-D finite element model using shell element and evaluation of acceptable initial crack size of VV by a linear elastic fracture mechanics. The fatigue crack growth is evaluated using the cracks modeled by the local 3-D finite element model to calculate a stress intensity factor K as a function of crack size. During the current quench, plasma current drops from 15[MA] to 0[MA] in 27[ms]. It is assumed that CD occurs at start-of-flat (SOF) and end-of-burn (EOB). As a result of structural analysis, the principal stress in outboard region is mainly compression in direction of troidal and in inboard region is mainly tension in the same direction. The maximum Von-Mises stress of about 129[MPa] appears at the joint of outer shell of equatorial port and toroidal rib at EOB. To study fracture mechanics analysis, two local models of VV are created from VV global element model in the two small regions in which maximum stress in inboard region and outboard region respectively appears. The local models of VV have a crack and the K values are calculated for various crack size whose depth are from 2[mm] to 10[mm] every 2[mm] and 15[mm]. The possibility of unstable fracture is evaluated by comparison of K value with fatigue fracture toughness Kc.　And the fatigue crack growth is calculated by use ⊿K -da/dN curve. As a result of this analysis, maximum K value is estimated to be about 20[MPam1/2] at the inboard region which has a semi elliptical crack with depth of 15[mm] and width of 80[mm]. There is no significant unstable fracture and crack growth within the anticipated number of CD in ITER scenario.

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