## 3 Structural Assessment of the Reference WCLL COB Segment BC Region
### Reference BC Region v1
#### 3.2.2 Results  
Another set of analyses have been launched in order to evaluate the structural behaviour of the up-to-date version of the Reference BC region, with an increased BC thickness equal to 40 mm. In Figure 9, the equivalent Von Mises stress field arose within the structure in NO and OP loading scenarios.  
Then, a stress linearisation procedure has been conducted along the same paths already considered for the BC region v0, and the fulfilment of the RCC-MRx design criteria has been checked. As to the NO loading scenario, the results are not reported for the sake of brevity, but similar values to those obtained for the previous configuration have been found. Looking at the OP loading scenario, the results of the RCC-MRx design criteria verification are reported in Table 2. As it can be observed, globally, the criteria are fulfilled, and some critical values are reached; compared with the results of the reference BC region v0 analysis, some criticalities have been mitigated.  
Figure 8: Reference BC region v0 vs. v1.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Level D**} \\ \cline{2-5}
**Path** & \(\mathbf{P_{m}/S_{m}}\) & \(\mathbf{(P_{m}+P_{b})/(K_{eff}S_{m})}\) & \(\mathbf{(P_{m}+Q_{m})/S_{cm}}\) & \(\mathbf{(P_{m}+P_{b}+Q+F)/S_{ct}}\) \\ \hline AB\_Cap & 0.363 & 0.267 & 0.287 & 0.090 \\ AB\_Cap2 & 0.336 & 0.269 & 0.331 & 0.163 \\ AB\_low & 1.328 & 1.020 & 0.835 & 0.213 \\ AB\_low & 1.248 & 0.866 & 1.033 & 0.232 \\ AB1\_mid & 0.576 & 0.472 & 0.360 & 0.128 \\ AB1\_up & 0.314 & 0.225 & 0.362 & 0.124 \\ CD\_low & 0.303 & 0.830 & 0.142 & 0.308 \\ CD1\_low & 0.228 & 0.629 & 0.230 & 0.189 \\ CD1\_mid & 0.429 & 0.353 & 0.532 & 0.187 \\ CD1\_up & 0.501 & 0.448 & 0.611 & 0.197 \\ EF\_low & 0.468 & 1.143 & 0.292 & 0.218 \\ EF1\_low & 0.478 & 1.139 & 0.420 & 0.313 \\ EF1\_mid & 0.265 & 0.212 & 0.360 & 0.082 \\ EF1\_up & 0.307 & 0.281 & 0.402 & 0.134 \\ EF2\_low & 0.419 & 0.680 & 0.259 & 0.181 \\ SPv1\_low & 0.788 & 1.010 & 0.496 & 0.160 \\ SPv1\_up & 1.091 & 0.818 & 0.456 & 0.098 \\ SPv2\_low & 0.940 & 0.955 & 0.513 & 0.163 \\ SPv2\_up & 1.281 & 0.869 & 0.325 & 0.050 \\ SPv3\_low & 0.959 & 0.654 & 0.813 & 0.204 \\ SPv3\_up & 1.056 & 0.725 & 0.865 & 0.241 \\ Cap1 & 0.406 & 0.765 & 0.359 & 0.149 \\ Cap2 & 0.320 & 0.542 & 0.308 & 0.151 \\ Cap3 & 0.209 & 0.626 & 0.172 & 0.092 \\ Cap4 & 0.170 & 0.523 & 0.166 & 0.075 \\ \hline \hline \end{tabular}
\end{table}
Table 2: RCC-MRx Level D criteria verification. Reference BC region v1.  
Figure 9: Von Mises stress field under NO and OP loading scenario. Reference BC region v1.  
Finally, results allow the conclusion that the first adopted improvement provided some enhancements in the structural performances of the considered BC region and, in particular, the Bottom Cap plate performances undergo an evident improvement. Some issues still remain within the vertical SPs and in the lowest region of the Cap, near the cooling channel. In any case, comprehensive analysis of the BC complete region, and the manifold region, is necessary to understand their contribution to its behaviour. Moreover, it is also important to take into account some additional elementary cells, firstly to be able to study in detail the horizontal SPh and, secondly, to ensure that the elementary cell housing the BC plate is far enough from the boundary conditions application and its structural response is not affected. Finally, to investigate in depth the thermo-mechanical behaviour of the BC region, a dedicated thermal analysis is necessary.