Final Development of the Helium Inlet for the ITER Toroidal Field Coils

The Toroidal Field Coils (TFC) for the ITER magnet system are large `D´ shaped coils consisting of a Winding Pack (WP) enclosed in a stainless steel (316LN) casing. The WP is a bonded structure of 7 Double Pancakes (DP), each made up of a stainless steel radial plate (RP) housing the reacted Nb3Sn circular cable-in-conduit superconductor (CICC), which operate at 4.5 K. The cooling of the WP is assured by helium feed in the CICC through one inlet for each DP at an average mass flow of 7.9 g/s in the conductor. The helium inlet is critical from a structural point of view because it has to withstand both static and cyclic strains in the order of (10.2±2.3)×10^-4 coming from energization of the TFC and plasma operation conditions. The assembly of the helium inlet around the conductor includes a fillet weld that makes it even more critical. This paper describes the analyses results performed for the (static and fatigue) structural assessment of the helium inlet. It describes the statistical approach followed to determine the number of cycles to be used in the validation tests.