## 5 Summary and Conclusions  
The topic of control and shutdown was introduced through a literature review and a reduction in the control approaches to a limited number of basic functions with different variations. In this study, the requirements for the control and shutdown systems for a reactor experiment were formulated, and based on these, an approach for the shutdown, i.e., splitting the lower part of the core with the reflector, and an approach for the control, i.e., a vertically movable radial reflector, were proposed. Both systems are usable for a zero-power system with a liquid as well as a solid core, and even more importantly, both systems somehow work at the integral system level and do not require the central part of the core to be disturbed, which will be the essential area for the experimental measurements. Both approaches, as singular systems, as well as their interaction, and the sensitivity of the control system were investigated through the use of a multitude of modeling and simulation results using deterministic and Monte Carlo tools of the SCALE package. The investigation of the shutdown efficiency assessed it between only moving the reflector and moving the reflector with increasingly sized layers of the core up to 30 cm. The comprehensive study indicated a variety of solutions, with a shutdown reactivity effect from \(-2000\) up to \(-8000\) pcm, depending on the configuration. The analysis of the proposed control approach was evaluated against the U-235 to indicate the control span with increasing U-235 enrichment, which was followed by the investigation of the control curve for the standard system delivering a control span of \(-18{,}000\) pcm. The sensitivity investigation was based on a variation of the reflector thickness by \(\pm 10\) cm, which led to a variation of \(\sim\pm 20\%\) in the control span, based on the slight core size variations resulting from the effect of changes to the reflector thickness. A control reactivity curve dependent on the stepwise downward movement of the reflector for systems with different thicknesses of the reflector was provided for all cases and the neutron spectrum change between the core with a reflector (lower core part) and without a reflector (upper core part). The interaction between both systems was analyzed by introducing a shutdown with different openings in conjunction with the reflector control system being in the position of a critical system delivering a shutdown reactivity curve with a maximum between \(-3500\) pcm for a 10 cm layer and \(-6200\) pcm for a 30 cm layer. The dependence of the shutdown system on the system size change due to the change in the reflector thickness was found to be marginal. A sensitivity study based on a system temperature change of \(\pm 50\) K led to a reflector movement of \(+24\) cm for \(+50\) K and \(-14.6\) cm for \(-50\) K to compensate for the related reactivity change induced by the temperature change. Finally, a consistency check between the multi-group Monte Carlo result, as used for this study, and a continuous energy Monte Carlo result using the same cross-section basis of SCALE was presented, which indicated a small change in the predicted control position. This inter-comparison of codes of the SCALE package with good agreement between them creates trust in the results obtained but indicates that there is room for improvement and demonstrates the need for validation experiments to assure the best possible results for future modeling and simulation of molten salt reactor systems. The current analysis was only applied to a very narrow window of operational temperatures in molten salt, which is related to the limited data availability. Thus, a much more comprehensive study will be required as soon as the relevant thermo-physical properties are available down to room temperature. Both approaches, the control through the movement of the reflector, and the shutdown through moving a layer of the core, require mechanical movement of core pieces with a significant mass.