The first 3D thermal-fluid-dynamic and structural analyses done for the design and pre-test assessment of the so-called Thermo-Cycle Mock-up (TCM), reproducing about 0.3 m2 of a flat first wall (FW) with relevant helium cooling channels, are presented, based also on previous computational and experimental activities conducted at KIT but limited so far to a single cooling channel with straight heated length. The TCM is the first of a series of FW mock-ups presently under construction, to be tested starting from 2015 in the large HELOKA facility at KIT. Here, the fluid dynamics in the 180° turns of the TCM cooling channels is investigated together with the effects of heat transfer between neighboring channels, when the plate is subject to steady-state heat fluxes in the range 0.3-0.5 MW/m2. Based on the computed temperature maps, the stresses in the TCM and the related damage figures for the main failure modes (i.e., ratcheting and creep/fatigue) are assessed. These are compared with allowable limits in code and standards for the qualification of the TCM design and related to the prediction of the behavior of the component in the actual fusion environment.