Investigation upon the dynamic structural response of a nuclear plant on aseismic isolating devices

The behaviour of a special isolating system for the Nuclear Island of an ADS Plant is here analysed, with a preliminary assessment of base isolation main effects on the building response to a typical earthquake excitation. After a general description of isolators and main principles of seismic isolation, the attention is focused upon the HDRB isolator and its major applications to date. The application to the ADS Plant is investigated through an iterative approach combining the results from a three-dimensional finite element model and simplified by-hand calculations taking into account the typical non-linear characteristics of considered isolators. The analysis results allow a comparison between the NI building seismic response for a basemat on classical foundations and for two different types of isolators. The comparison is focused on the acceleration floor response spectra evaluated at the reactor support level, a basic concern in the main vessel seismic design. Given results highlight the drastic reduction of considered floor accelerations as the base isolation major effect. The criteria presently recommended for the stability of isolated buildings are also verified.