Untersuchungen zum Ratcheting von Segmenten der ''Ersten Wand'' zukuenftiger Fusionsreaktoren unter zyklischer thermischer und mechanischer Belastung

During the operation of a fusion reactor, the first wall elements are heated from the plasma-faced side and cooled from the blanket side. This leads to thermal stresses due to inhomogeneous temperature fields. Because of the pulsed operation of a tokamak these stresses are of cyclic nature. During disruptions or vertical plasma movements additional mechanical stresses occur in the first wall, caused by the interaction of the induced currents and the magnetic fields. These electromagnetic stresses may lie above the yield stress of the structural material. From the interaction of thermal and mechanical forces, a complex stress state is achieved which under certain circumstances may lead to premature failure or to progressive plastic deformation (ratcheting). In order to study the boundary conditions for the occurrence of ratcheting, a testing rig has been erected at KFA. In this rig small scale mock ups of the first wall, concerning the design of ITER-CDA stage, have been tested under conditions similar to those expected during the operation of ITER. In addition to the experimental work, theoretical analysis of the ratcheting phenomenon was carried out. Using simplified beam models, so-called BREE diagrams were developed to characterise the structural behaviour as a function of the applied primary and secondary stresses. The results were compared to existing design tools and the special features of ratcheting under bending conditions were discussed. In addition numerical calculations, using the finite element program ABAQUS, were carried out. In these calculations the temperature and stress fields in the mock-ups were investigated and the influence of the material behaviour on the ratcheting-effect was studied. Due to the fact that a decision about the design of the first wall is not yet made and the ratcheting-effect is strongly dependent on the exact design, the investigations in this work shall give a common access to the problem of ratcheting of first wall segments for dominating bending loading. (orig.)SIGLEAvailable from TIB Hannover: RA 831(3250) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman