Design and issues of the ITER in-vessel components: ITER Joint Central Team and Home Teams

Abstract

This paper surveys the status of the design of the in-vessel components for ITER, in particular the major components, namely the vacuum vessel, blanket and first wall, and divertor, and the interface of selected ancillary systems such as those used for RF heating and current drive, and for diagnostics. The vacuum vessel is a double-walled structure constructed from two toroidal shells joined by ribs. The space between the skins is filled with shield plates directly cooled by water. The structural material is 316 LN IG (ITER grade). Toroidal supports joining the vessel midplane ports with the TF structure limit possible differential toroidal displacements, as might occur due to seismic or vertical displacement events (VDEs). A variety of load conditions corresponding to normal and off-normal loads have been considered and in all cases peak vessel stresses are within allowables. The blanket system consists of approximately 700 modules, each weighing ∼4 t. The integrated first wall consists of a beryllium-tiled copper mat bonded to the water-cooled SS shield block. The copper mat functions as a heat sink and has imbedded in it an array of SS tubes providing water cooling. The modules are mechanically attached to a toroidal backplate. Loads due to centered disruptions are reacted via hoop stress in the backplate, whereas net vertical and horizontal loads such as those arising from VDEs are transferred through the backplate and divertor supports to the vessel. A double-wall backplate has been selected owing to structural advantages, longer coolant hold up times, and simplification of the manifold layout. Breeding blanket modules have been designed to replace the shield blanket modules within the same dimensional envelope. A solid breeder has been selected as reference breeder material. TBRs=0.8 are calculated which, together with tritium supplied from external sources, should permit a sufficient tritium supply for the EPP. The divertor design is based on a vertical target configuration. With the addition of a modest impurity fraction the divertor plasma is expected to detach from the target plates along the separatrix. The semi-detached mode of operation lowers the peak heat flux from ≥ 30 to ≤5 MW m −2. The high-heat flux (HHF) components in the divertor consist of a water-cooled copper heat sink with CFC and W tiles. A number of methods of joining CFCs, W and Be to copper are being successfully developed in the R&D program. Component testing has indicated that a heat removal of 20 MW m −2 is achievable. The divertor consists of 60 cassettes mounted on toroidal rails anchored to the bottom of the vessel. The HHF components are mounted on these cassettes and are designed to be replaceable in a hot cell. Both the blanket modules and the divertor cassettes are designed to facilitate remote replacement, with minimal turn-around time. ICRF, ECRF and NBI heating and current drive systems are under design, each at a nominal power level of 50 MW. Problems and solutions associated with RF and diagnostic interfaces are illustrated by description of the integration of ECRF, ICRF and LIDAR diagnostic systems.