Abstract: A high-temperature nuclear reactor having spherical fuel elements which are rranged approximately ring-shaped about a graphite core, and in particular, a massed-sphere nuclear reactor providing for inherent passive stabilization in the event of damage. The inventive high-temperature reactor of the above-mentioned type distinguishes itself in that the graphite core is formed by a pile or mass of graphite spheres. Through the intermediary of such an axial graphite sphere region, the maximum temperature of the fuel elements of the core can be limited in the event of encountered damage in a manner similar to that as would be the case for a compact graphite column.