In view of the strongly increasing energy demand of the world in future, the nuclear energy has to be used to a large extent, especially, if corresponding with the requirements of climatic research, the use of fossil energy carriers has to be limited. However, for a spread world-side use of nuclear energy a new safety quality has to be required. Solutions to a catastrophe-free nuclear energy have to be verified and introduced. By this is meant that the radioactive fission products stay at all imaginable malfunctions within the reactor plant and that no radiologically caused incident-consequences occur outside the plant. This requirement has to be met for all malfunctions which can occur from internal causes or from predictable external ones. There are several intial steps in the world in order to reach this objective. On the one hand, reactor safety buildings are being developed which are to retain the occurring core-melt at light water reactors. ON the other hand, technical solutions are possible at which core-melting can be excluded by lay of nature and at which the radioactive fission products can be dept back in the fuel elements at all malfunctions. These reactor systems - as example here the correspondingly developed high-temperature reactor should be mentioned - show under all conditions of malfunctioning nuclear, thermal, chemical and mechanical stability.