Thermo-structural assessment of the limiter inboard first wall design of the Divertor Tokamak Test facility

The Divertor Tokamak Test facility (DTT) aims at investigating integrated power exhaust solutions that can be relevant for DEMO and future power plants. Such an ambitious goal imposes several constraints on the engineering design of the actively cooled plasma-facing components (PFCs) of DTT. For instance, the First Wall (FW) must withstand thermal and electromagnetic loads that arise during both normal and off-normal operations of various plasma scenarios. In particular, the Limiter Inboard FW (LIFW), covering 50 % of the IFW, has been designed to cope with plasma limited configurations, i.e. when the plasma interacts with the solid wall. Each module consists of seven long (2.3 m) coaxial pipes made of CuCrZr alloy. Owing to the high heat loads expected, the LIFW PFCs are based on the ITER-like W-monoblock design and the plasma-facing surface, protruding radially towards the plasma with respect to the standard IFW, has a toroidal shaping that helps distribute evenly the heat load. In the present work, the technological limits of the proposed LIFW design are assessed. Based on the hydraulic conditions of the cooling water, the maximum power that can be handled by the LIFW system is evaluated under the assumption of a safety margin from the critical heat flux (CHF). Moreover, the thermo-structural behavior of a LIFW unit is simulated in ANSYS under realistic boundary conditions. In this context, a parametric distribution of the thermal load is modelled as a function of the input power and the expected spatial-temporal evolution of the plasma “footprint”. Moreover, realistic kinematic boundary conditions, representative of the pinned supports, have been included in the structural integrity assessment of the pipe, carried out according to the ITER SDC-IC design criteria (design-by-analysis approach). Preliminary results suggest that the maximum peak heat flux that can be handled by the LIFW design falls in the range 5–8 MW/m2. This range is compatible with the DTT “Day0” scenario, when, due to the lesser knowledge of machine control, the most critical limiter operations may occur. Nonetheless, studies on the full power scenarios confirmed that in the ramp-up phase the maximum conductive heat load shall be lower than 1 MW/m2 therefore the calculated performances can be considered adequately safe. After the fabrication of small-scale mock-ups, the lifetime of such components will be assessed experimentally, by means of cyclic thermal fatigue high heat flux tests.