Nuclear power has been extensively used in space applications but in very few cases it entailed the use of nuclear fission reactors. The paper deals with a feasibility study of a space nuclear reactor for planet settlements, based on a “Generation III+” technology, specifically the integral type PWR one, currently under study in several projects (e.g. IRIS, CAREM, IMR, SMART) for its simplicity, compactness and cost reduction, but mainly based on already proven technology. This approach was suggested by the following constraints, typical in research activities for space applications, especially when nuclear is considered: to obtain a solution which has to be extremely reliable, moderately expensive in the R&D program, deployable in a reasonable period of time, safe and operable/controllable with no human intervention for several years. These requirements have been coped with by means of a reactor design based mainly on the well proven PWR technology of present terrestrial reactors. The fuel selection, the core configuration and related burnup, the primary and conversion systems, the reactivity and system control as well as preliminary considerations on safety are presented. The space nuclear reactor is envisaged to be suited mainly for stationary needs on a planet, by producing electrical energy of the order of 100 kW for nearly 4000 days. The obtained results are fully satisfactory and suggest to continue the study to reach a more detailed design.