The analysis of one-mass and two-mass models indicates that the earthquake-generated horizontal forces and deformations of the main structures of a nuclear power plant can be reduced by a factor of about ten times by mounting the overall power plant building on a recently developed base-isolation system. The very high forces which the ‘resonant appendage‘ effect may induce in some critical components (such
 as fuel elements, control rods and essential piping) may be reduced by a factor of 40 or more times by the isolation system. The parameters of
 the isolation system have been chosen as appropriate to the level of protection which should be provided for a nuclear plant in a seismically active area. Consideration is given to flexible mounts and dampers suitable for such an isolator.