## 3 Thermo-Mechanical Analysis and Further Design Improvement of the WCLL COB Segment TC Region
### \"TC Region-Mod\" Thermo-Mechanical Analysis and Results  
Once proved that the \"TC region-mod\" geometric configuration fulfils the design requirement on the Eurofer maximum temperature under nominal conditions, thermo-mechanical analysis under NO and OP steady-state loading scenarios is performed. The obtained results are processed in order to perform a stress linearization procedure for the verification of the corresponding RCC-MRx Level A and Level D criteria. To this purpose, a proper set of paths (i.e., stress lines) is selected on the basis of the analysis of the von Mises equivalent stress spatial distributions, which allows putting the focus on the most stressed regions. In particular, as the OP loading scenario represents the design basis accident, the first assessment is done looking at the results obtained under this accidental loading scenario. Hence, in Figures 8-10, the von Mises equivalent stress field calculated within TC, FW-SWs and SPs domains under OP loading conditions are depicted, respectively, with the indication of the path locations. Figure 9: OP von Mises equivalent stress field and path locations within FW-SWs domain. It has to be observed that, as for SPs, the paths are oriented through the plate thickness for both horizontal (toroidal-radial--TR) and vertical (polodial-radial--PR) SPs. Looking at the von Mises equivalent stress spatial distributions, it can be observed that some hotspots (i.e., isolated red stains in the distributions) are visible, mainly originated by the action of ferromagnetic forces which are applied as concentrated forces in the model. Hence, in close proximity to these stains, no significant evaluation in terms of RCC-MRx code application is possible. Moreover, it can be clearly observed that most of the assessed domain experiences von Mises stress values lower than 500 MPa, which is usually an index of promising structural behavior. The worst situation seems to be predicted for the SPsv in the TC domain. Figure 10: OP von Mises equivalent stress field and path locations within SPs domain. slice, since values greater than 500 MPa are calculated in a large volume. Once the proper paths are selected, a stress linearization procedure is performed in order to compare the equivalent stress values to the stress limits prescribed by the RCC-MRx code, using the Level D criteria, as the OP scenario represents an accidental condition. In particular, four criteria are taken into account for the structural evaluation: immediate excessive deformation (IED, \(\rm P_{m}/S_{m}\)), immediate plastic instability (IPI, \(\rm(P_{m}+P_{b})/(K_{eff}\times S_{m})\)), immediate plastic flow localization (IPFL, \(\rm(P_{m}+Q_{m})/S_{em}\)) and immediate fracture due to exhaustion of ductility (IF, \(\rm(P_{m}+P_{b}+Q+F)/S_{et}\)). While the first two criteria only consider the primary stresses (membrane, \(\rm P_{m}\), and bending, \(\rm P_{b}\)), the others take into account also secondary stresses (membrane, \(\rm Q_{m}\), and total, \(\rm Q\)) and peak stress (F) occurring along the analyzed path. For each criterion, the stress limit values (\(\rm S_{m}\), \(\rm S_{em}\), \(\rm S_{et}\), depending on the considered criterion) are calculated, for the service level D, to which the OP loading scenario relates, in accordance with the structural material and the average path temperature. The obtained results are summarized within Tables 1-3 regarding criteria verification for paths located within the TC, FW-SWs and SPs respectively. In these tables, the ratios between the equivalent stress intensities and the corresponding stress limits are reported, as prescribed by the code. Hence, values greater than 1.0 (highlighted in red, when they arise) mean that the criterion is not fulfilled in that path. Moreover, values very close to the critical one (>0.9) are reported in orange to indicate the stress level closeness to the limit. Concerning TC, the failures in the criteria verification are due to both primary and secondary stress.