The new high-flux neutron source FRM-II is constructed as a reactor to replace the Munich Research Reactor FRM which has been in operation since 1957. Based on its sophisticated technical concept, the FRM-II will achieve a useable neutron flux 50 times higher at a reactor power (20 MW) five times higher than that of the FRM. A large-scale heavy-water-moderator tank is used to establish this high flux in a considerably greater usable volume and practically only by slow neutrons which are particularly well suited for utilization.