Development of seismic protection system for design extension conditions (SPSDEC) is suggested for enhancing safety of operation of NPP located on the territories with unfavorable seismic conditions. The idea of the system consists of the creation of a network of seismic stations arranged at a certain distance from the NPP and equipped with data transmission system. In case of detection by seismic sensors of movements of the ground with magnitude of vibrations exceeding a certain preset value, seismic stations transmit over radio-channel a signal indicating exceedance of the setting before the seismic wave reaches the NPP. This allows initiating transition of the reactor to subcritical operation mode prior to the beginning of destruction of equipment and reactor building. Ensuring reliable protected communication is achieved by simultaneous use of three radio-channels arranged in accordance with TETRA, WiMAx and LTE standards, as well as by the application of appropriate cryptography, authentication and data protection methods for preventing data corruption. Analysis was performed for determining optimal distance between seismic stations and the NPP and optimal number of these stations was determined for the following two options of arrangement of seismic stations: radial arrangement surrounding the NPP and arrangement along the direction towards the place with the highest probability of earthquake incipience. Layout was suggested of multilevel majoritarian data processing for excluding false triggering of the system. Conclusions were formulated on the enhancement of safety of NPP operation and significant reduction of probability of emergency situations due to the generation of anticipatory signals to reactor shutdown systems in case of earthquakes with intensity exceeding maximum design earthquake.