Seismic characteristics of the WWER-1000 reactor

For an analysis of seismic characteristics the model of the WWER-1000 reactor is divided into two systems: the system of horizontal motion and the system of vertical motion. The model for horizontal motion is continuous, for vertical motion discrete. It follows from the calculations made that the eigenfrequencies of the WWER-1000 reactor model for vertical motion are several times higher than the eigenfrequencies of the WWER-440 reactor. The conclusion is arrived at that the WWER-1000 reactor is more resistant to seismic excitation than the WWER-440, this both with regard to vertical and horizontal motion. It is evident from calculated eigenfrequencies that only the first eigenfrequency falls into the zone of seismic excitation (up to 40 Hz). Its shift outside this zone is mainly affected by the change of longitudinal rigidity of the reactor shaft and the rigidity of the fuel assembly springs. Additional adjustment of spring rigidity by one order of magnitude appears acceptable. (Z.M.)