## 6 Analysis of the Influence of the Reflector Material on the Neutron Flux
### Control Curve and Shutdown  
In a final step, the consequences of the change in the reflector for the reactor control and shutdown system as developed in [6] had to be evaluated to ensure that the changed reflector still allows the application of the envisaged control and shutdown approach. The use of the smaller core with the copper reflector led to a significant increase in the control span compared with the original larger core with the NaCl reflector (see Figure 17). The increase in the control span can be explained by the significantly stronger effect of the reflector on core criticality, which was finally reflected through the opportunity to decrease the size of the core while the core still stayed critical. Thus, the control approach cannot only be kept when using the copper reflector: the approach will even become more efficient and the control span will become wider, which allows the higher flexibility of the reflector control and the core design.  
The evaluation of the consequences of changing to a significantly more effective reflector material on the shutdown system is given in Figure 18. The splitting of 30 cm in this layer of the core, including the reflector, delivers a significantly higher shutdown reactivity with the smaller core than in the reference case with the NaCl reflector. Thus, the envisaged shutdown approach would not be negatively influenced by the change to a much more efficient reflector material. It would even allow a potential reduction of the core layer which has to be split away. This optimization should be carried out when a definitive decision has been taken regarding the reflector material and the final core design.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Reflector** & **Cost [\$/ton]** & **Density [ton/m\({}^{3}\)]** & **Cost [\$/m\({}^{3}\)]** & **Cost Estimate [\$]** \\ \hline SS304 30 cm & & & & \\ ([[https://www.stindia.com/stainless-steel-304-316l-price-per-kg-india.html#price](https://www.stindia.com/stainless-steel-304-316l-price-per-kg-india.html#price)]([https://www.stindia.com/stainless-steel-304-316l-price-per-kg-india.html#price](https://www.stindia.com/stainless-steel-304-316l-price-per-kg-india.html#price))\_per\_kg, accessed on 1 April 2021) & 4380 & 7.390 & 34,733 & 88,372 \\ \hline Lead 50 cm & & & & \\ ([[https://markets.businessinsider.com](https://markets.businessinsider.com)]([https://markets.businessinsider.com](https://markets.businessinsider.com)), accessed on 1 April 2021) & 2026 & 11.343 & 22,980 & 132,728 \\ \hline Copper 20 cm & & & & \\ ([[https://markets.businessinsider.com](https://markets.businessinsider.com)]([https://markets.businessinsider.com](https://markets.businessinsider.com)), accessed on 1 April 2021) & 7735 & 8.94 & 69,150 & 105,458 \\ \hline \end{tabular}
\end{table}
Table 2: Cost comparison for different reflector configurations.  
\begin{table}
\begin{tabular}{c c c} \hline  & **Volume Saving** & **Case** \\ \hline All reflectors & 20.3\% & Pb 30 cm to 50 cm \\ \cline{2-3}  & 10.4\% & Cu 20 cm to 30 cm \\ \hline Axial reflector & 4.1\% & Pb 30 cm to 50 cm \\ \cline{2-3}  & 2.2\% & Cu 20 cm to 30 cm \\ \hline Radial reflector & 16.9\% & Pb 30 cm to 50 cm \\ \cline{2-3}  & 8.5\% & Cu 20 cm to 30 cm \\ \hline \end{tabular}
\end{table}
Table 3: Study of potential volume savings resulting from an increase in the reflector thickness at different places.