This study focuses on thermochemical cavity-type reactor, with a reactive material directly irradiated by concentrated solar energy. General tendencies of reactor performance are analyzed as a function of the reactor geometry. The objective is to define a simplified model that can be adapted easily to different reactor designs or different operating conditions. For this reason, the chemical reaction is not precisely fixed but rather characterized by a reaction temperature and a useful power consumed by the endothermic reaction, inside the reactive material. In order to increase the efficiency, two new reactor designs are proposed. These designs allow obtaining a nonuniform distribution of the useful power consumed by the reaction with the depth in a circular cylindrical cavity (z-axis). This is done in two ways: by varying the reactive material thickness along the axis or by varying its density at a constant thickness. The results show that these reactor concepts lead to a more uniform temperature distribution along the z-axis and a diminution of the heat losses. Thus, the reactor efficiency can increase significantly. The results of the simplified model can be used as a system predesign. A more accurate CFD model could be used afterward to refine the optimal shape.