## 4 Thermal and Structural Analysis and Design Improvements of the BC Region
### The First Update (v1) of the BC Region Design
#### 4.1.2 Results  
Firstly, the thermal analysis of the entire BC region has been performed, with the aim of ensuring that the thermal requirements, namely that the Eurofer temperature stays below 550 \({}^{\circ}\)C, are fulfilled. In Figure 12, the thermal field arising within the Eurofer domain is reported. As can be observed, the temperature remains below the suggested limit, reaching a maximum value of 536 \({}^{\circ}\)C at the FW-SWs bend regions in the bottom part, in correspondence with the Cap plate. Globally, high temperatures can be observed in the FW-SWs bend region due to the cooling channels layout. In particular, the bending radius should be properly tuned in order to minimise the distance of the channel from the Tungsten layer. Finally, no issues can be observed within the Cap plate, as reported in Figure 13, reaching a maximum temperature value of about 520 \({}^{\circ}\)C.  
Figure 11: Volumetric heat power density within SB, DWTs and PbLi. \begin{table}
\begin{tabular}{c c c} \hline \hline \(\mathbf{HTC_{CC}}\) & \(\mathbf{HTC_{DWTs}}\) & \(\mathbf{HTC_{DWTs,rec}}\) \\ [**W/m\({}^{2}\)-K**] & [**W/m\({}^{2}\)-K**] & [**W/m\({}^{2}\)-K**] \\ \hline
36,821.2 & 14,862.4 & 23,255.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: HTC values used for cooling channels and DWTs coolant. Then, the steady-state structural analyses of the entire BC region were performed under the NO and OP loading scenarios, and the fulfilment of the RCC-MRx design criteria were checked. In Figures 14 and 15, the Von Mises equivalent stress fields arising within the structure are reported. Globally, the structure appears to be more stressed in the FW region and, in particular, in correspondence with the two bends. Instead, looking at the OP scenario, the vertical SPs of the last elementary cell, housing the BC plate, experience high stress values. In any case, it has to be underlined that the high stress values predicted in correspondence of the BC plate/SPv interface may be affected by the adopted modelling strategy, foreseeing a simple \"bonded\" contact without any condition on the mesh continuity. The same modelling strategy has been considered for the FW-SW/BC plate interface. Moreover, as can be observed, there are some stress hotspots due to the local application of the EM loads. Those regions have not been evaluated from the structural point of view, and no paths have been considered near them. Figure 12: Thermal field arising within SB. BC region v1. Figure 13: Thermal field arising within Cap. BC region v1. Figure 14: Von Mises stress field under NO loading scenario. BC region v1. Figure 15: Von Mises stress field under OP loading scenario. BC region v1. A stress linearisation procedure was performed along the selected paths, and the RCC-MRx criteria, related to Level A and D, for the NO and OP loading scenario, respectively, were checked. In particular, 20 paths were considered within the FW region (Figure 16), 13 paths within the SPs and 3 along the Cap plate (Figures 17 and 18). Looking at the results within the paths considered along the FW and the Cap (Tables 4 and 5), some issues can be observed within the Cap and in the so-called path AB at every poloidal height (A, B and C). Because the not-matched criteria are those involving secondary stress, it is quite possible that a slight revision of the FW-SW cooling system will have to be performed. However, because these verifications are narrowly failed, this possible improvement is judged to be of the second order, and it can be postponed to a further phase. Instead, as to the SPs results reported in Tables 6 and 7, besides the criticalities due to secondary loads, it is possible to observe that globally, the Level D criteria are not fulfilled, especially the criterion against the Immediate Excessive Deformation (P\({}_{\text{m}}\)/S\({}_{\text{m}}\)), suggesting a revision of the SPs' thicknesses.