Thermochemical processes present a cyclic working mode combining two active phases separated by intermediate phases. A model coupling the solid-gas kinetics and heat and mass transfers in the reactive media was developed to simulate this cyclic working mode. With this model, the optimum values of the working conditions for a fixed reactor configuration had been defined in a previous work. The objective of this paper is to define the best reactor configuration to produce a given cold mean power. Towards this goal, the first stage consists of analyzing the influence of the two parameters characterizing the configuration: the reactor mass and the radius. This sensibility study is then used in a concrete application where a pre-fixed mean power is required.