ITER divertor cassette and PFC attachment structural design

Abstract

High heat fluxes and high electromagnetic loads make for a challenging combination in the design of the ITER divertor cassette and plasma facing component (PFC) attachments. The cassette body must be able to handle high bending moments imposed by the electromagnetic (EM) forces in areas with cross sections that are reduced due to the coolant channel, vacuum port, gas box, shoe and PFC cut-outs. The ITER divertor cassette design incorporates removable, high heat flux components (PFCs) whose lives are shorter than the cassette body due to the more severe loading conditions. The PFC attachments must be designed to withstand the high EM and thermal loads and have limited constraint in order to minimize thermal stresses. The EM loads on the divertor cassette result in typical forces on the PFCs in the order of 1 MN and bending moments on the body of 1 MN-m. The forces used in the structural design represent a fast Vertical Displacement Event (VDE) with a 100 ms quench. In addition, thermal loads must also be considered in the design. The surface heat fluxes range from a nominal of 5 MW/m/sup 2/ to a peak of 20 MW/m/sup 2/ and are incident on the PFC surfaces. Volumetric heating also occurs, peaking at 10 W/cm/sup 3/ in the PFCs and 0.5 W/cm/sup 3/ in the body. These surface heat fluxes and volumetric heating result in differential temperatures and growth between the PFCs and cassette body. The attachment concepts must themselves be maintained within allowable temperatures, which limits their size and requires a certain proximity to coolant. The heat fluxes require the body to have frequent coolant channels to maintain temperature limits. These must be placed so they do not compromise the structural integrity of the cassette. Cassette body cross sections and PFC attachments must be designed to withstand these loads. General cassette design guidelines and cross sectional requirements have been examined for the body. A variety of attachment concepts have been examined for the different PFC locations and conditions. Dumbbell, keyhole, hat, L- and T-shaped attachments have been examined as well as a lug with a mandrel expanded hollow pin.