  The paper explores the linear and nonlinear dynamic interaction between the
reactor and the auxiliary buildings of a Nuclear Power Plant, aiming to
evaluate the effect of the auxiliary building on the seismic response of
crucial components inside the reactor building. Based on realistic geometrical
assumptions, high-fidelity 3D finite element (FE) models of increasing
sophistication are created in the Real-ESSI Simulator. Starting with elastic
soil conditions and assuming tied soil-foundation interfaces, it is shown that
the rocking vibration mode of the soil-reactor building system is amplified by
the presence of the auxiliary building through a detrimental out-of-phase
rotational interaction mechanism. Adding nonlinear interfaces, which allow for
soil foundation detachment during seismic shaking, introduces higher excitation
frequencies (above 10 Hz) in the foundation of the reactor building, leading to
amplification effects in the resonant vibration response of the biological
shield wall inside the reactor building. A small amount of sliding at the
soil-foundation interface of the auxiliary building slightly decreases its
response, thus reducing its aforementioned negative effects on the reactor
building. When soil nonlinearity is accounted for, the rocking vibration mode
of the soil-reactor building system almost vanishes, thanks to the strongly
nonlinear response of the underlying soil. This leads to a beneficial
out-of-phase horizontal interaction mechanism between the two buildings,
reducing the spectral accelerations at critical points inside the reactor
building by up to 55% for frequencies close to the resonant one of the
auxiliary building. This implies that the neighboring buildings could offer
mutual seismic protection to each other, in a similar way to the recently
emerged seismic resonant metamaterials, provided that they are properly tuned
during the design phase.
