## 4 Structural Analysis of the Reference COB Segment
### Results  
Steady state analyses of the reference COB segment under different loading scenarios were performed with the aim of evaluating its structural behaviour, as well as verifying that the safety criteria of the RCC-MRx for the structural material were fulfilled. So, the von Mises equivalent stress fields obtained for each different loading scenario are reported in Figures 11 and 12, in which only the Eurofer structural material is displayed. The deformed vs. undeformed shapes are likewise depicted in Figures 13 and 14, also with the displacement fields for each assessed scenario. In particular, the deformed shapes are shown with an isotropic amplification factor equal to 20. Looking at the displacement fields, in each operating scenario analysed, the maximum displacement occured along the radial direction, as well as, looking the von Mises stress fields, the equatorial region being the particularly stressed one. In Table 5 the maximum and minimum values of displacement along all directions for all the assessed scenarios are reported, where Ur, Ut and Up indicate the displacements along the radial, toroidal and poloidal direction, respectively. The values obtained show the same trend and the largest displacement occurs in all the assessed scenarios along the radial direction, with the highest value raised in the OP loading scenario. Moreover, in the UVDE scenario, when the EM loads are considered at the time step of 11.585 s (maximum of radial moments), a larger displacement in toroidal direction than in the other scenarios can be highlighted. Figure 11: Von Mises stress field under NO and OP loading scenarios. Figure 12: Von Mises stress field under UVDE (t = 11.52 s and t = 11.585 s) loading scenarios. Figure 14: Deformed vs. Undeformed shapes under UVDE (t = 11.52 s and t = 11.585 s) loading scenarios. Figure 13: Deformed vs. Undeformed shapes under NO and OP loading scenarios. In the end, a stress linearization procedure was performed along some significant paths located within the most stressed regions of the structure. Then, the fulfilment of Level A, C and D criteria, namely, for the NO, UVDE and OP loading scenario, respectively, prescribed by the RCC-MRx design code along them was checked. In particular, four criteria were taken into account for the structural evaluation: Immediate Excessive Deformation (IED), Immediate Plastic Instability (IPI), Immediate Plastic Flow Localization (IPFL) and Immediate Fracture due to exhaustion of ductility (IF). While the first two criteria only considered the primary stresses, the others also took into account secondary stresses occurring along the analysed path. For each criterion, the stress limit values were calculated, for the service level (A, C or D) to which each loading scenario analysed relates, in accordance with the structural material and the average path temperature. Therefore, since the cooling channels located within the FW-SW region were not modelled to reduce the computational burden, only the SPs grid was considered from the mechanical point of view and some paths lying on the poloidal-radial and toroidal-radial SPs (Figure 15), at three different poloidal height, highlighted in red and blue in Figure 15, were individuated. The obtained results are reported in Tables 6-9, also representing the average temperature values arising within each path. For each criterion, the ratio between the equivalent stress value and the corresponding stress limit is reported in the tables where the values greater than 1 are highlighted in red, indicating that the criterion was not fulfilled within the selected path. The evaluation of the results of the RCC-MRx criteria indicated that the vertical SPs were particularly stressed, in particular the path named SPv2, in each poloidal height considered. In each considered loading scenario, these paths did not totally fulfill  
Figure 15: Paths within SPs grid in the equatorial region.