## 4 Thermal and Structural Analysis and Design Improvements of the BC Region
### The Second Update (v2) of the BC Region Design
#### 4.2.2 Results
Moreover, the results have been compared, and the percentage of variation, calculated as, for example, (SPv1_Cave - SPv1_C)/SPv1_Cave, is also reported. Figure 22: Von Mises stress field under OP loading scenario. BC region v2. Looking at the results along the SPv paths globally, it can be observed that the average values obtained are lower than the reference ones. This behaviour indicates that the local phenomenon, which in this case is the strategy adopted to model the contact between the SPs and the Cap, actually affects the structural behaviour in those regions. The same statement cannot be said, however, looking at the paths individuated along the FW and Cap. In these cases, in fact, the average and the reference path values of the ratio are equal or even worse, which suggests that the structural response is not influenced by any singularities or any localised peak of stress. Finally, it can be concluded that, as for the SPs' structural behaviour, particular attention has to be paid to the modelling strategy in order to prevent this interfering with their performances. In any case, additional improvements to the geometric layout should  
Figure 23: Selected set of paths for SPv1_C. \begin{table}
\begin{tabular}{c c c c} \hline  & **SPv1\_C** & **SPv1\_Cave** & **Var. [\%]** \\ \(\mathrm{P_{m}}/\mathrm{S_{m}}\) & 1.226 & 1.141 & \(-\)7.48\% \\ \((\mathrm{P_{m}}+\mathrm{P_{b}})/(\mathrm{K_{eff}}\mathrm{S_{m}})\) & 0.843 & 0.770 & \(-\)9.49\% \\ \((\mathrm{P_{m}}+\mathrm{Q_{m}})/\mathrm{S_{em}}\) & 1.038 & 0.957 & \(-\)8.42\% \\  & SPv2\_C & SPv2\_Cave & Var. [\%] \\ Level D & \(\mathrm{P_{m}}/\mathrm{S_{m}}\) & 0.925 & 0.857 & \(-\)7.86\% \\ \((\mathrm{P_{m}}+\mathrm{P_{b}})/(\mathrm{K_{eff}}\mathrm{S_{m}})\) & 0.653 & 0.590 & \(-\)10.63\% \\ \((\mathrm{P_{m}}+\mathrm{Q_{m}})/\mathrm{S_{em}}\) & 0.424 & 0.354 & \(-\)19.74\% \\  & SPv3\_C & SPv3\_Cave & Var. [\%] \\ \(\mathrm{P_{m}}/\mathrm{S_{m}}\) & 1.174 & 1.123 & \(-\)4.56\% \\ \((\mathrm{P_{m}}+\mathrm{P_{b}})/(\mathrm{K_{eff}}\mathrm{S_{m}})\) & 1.131 & 1.006 & \(-\)12.41\% \\ \((\mathrm{P_{m}}+\mathrm{Q_{m}})/\mathrm{S_{em}}\) & 0.660 & 0.612 & \(-\)7.86\% \\ \hline \end{tabular}
\end{table} 
Table 8: RCC-MRx Level D criteria comparison within SPv. \begin{table}
\begin{tabular}{c c c c c} \hline  & **AB\_Cap1** & **AB\_Cap1 ave** & **Var. [\%]** \\  & \((\mathrm{P_{m}}+\mathrm{Q_{m}})/\mathrm{S_{em}}\) & 1.140 & 1.153 & 1.07\% \\  & \(\mathrm{AB\_Cap2}\) & \(\mathrm{AB\_Cap2}\) & Var. [\%] \\ Level A & \((\mathrm{P_{m}}+\mathrm{Q_{m}})/\mathrm{S_{em}}\) & 1.047 & 1.041 & \(-\)0.55\% \\  & \(\mathrm{AB\_C1}\) & \(\mathrm{AB\_C1}\) & \(\mathrm{AB\_C1}\) & Var. [\%] \\  & \((\mathrm{P_{m}}+\mathrm{Q_{m}})/\mathrm{S_{em}}\) & 0.923 & 0.939 & 1.66\% \\  & \(\mathrm{AB\_C2}\) & \(\mathrm{AB\_C2}\) & \(\mathrm{AB\_C2}\) & Var. [\%] \\  & \((\mathrm{P_{m}}+\mathrm{Q_{m}})/\mathrm{S_{em}}\) & 1.211 & 1.223 & 1.05\% \\ \hline \end{tabular}
\end{table} 
Table 9: RCC-MRx Level A criteria comparison within FW and Cap. also be helpful to further enhance the structural behaviour so that the RCC-MRx criteria are fulfilled with a great margin. Instead, looking at the FW and Cap response, since the results of the RCC-MRx criteria verification show that the criterion taking into account the secondary stresses (namely IPFL, (P\({}_{\rm m}\) + Q\({}_{\rm m}\))/S\({}_{\rm em}\)) is mostly not fulfilled in this region, a slight revision of the FW-SWs cooling system is necessary to obtain a significant performance improvement. Moreover, it can also be observed that the selected Cap thickness of 40 mm may be too high with respect to that of the surrounding components (FW and SPs). Hence, the Cap plate could act as a grip in their respect, preventing thermal expansion and then inducing secondary stress.