Seismic analysis of primary sodium pump of prototype fast breeder reactor

This paper deals with seismic analysis of primary sodium pump of 500 MWe Prototype Fast Breeder Reactor (PFBR) by time history analysis. The associated fluid mechanics equations for determining stiffness coefficients for hydrostatic bearing (HSB) are formulated and solved by integrating with the governing structural dynamics equations. Thus, the stiffness coefficients of HSB are computed as function of eccentricity, speed and angular orientation of shaft at every solution time step. The maximum stress intensity values in the flywheel-motor support shell, pump shell and shaft are insignificant (<20 MPa). Hence, the structural integrity is assured for pump parts. The seizure of pump is found to be a critical issue under seismic events. The eccentricity of 60 μ experienced by the shaft during normal operation, increases to 250 μ under SSE. Since it is < 400 μ, the radial clearance, there is no problem of pump seizure. However, at speeds lower than 265 rpm, the eccentricity of shaft is higher than radial clearance and hence shaft can impact on the shell. Under OBE, up to 20 % speed (∼120 rpm), there is no impact. The peak impact force experienced by shaft and shell at HSB at 235 rpm under SSE is < 3 t, which may not cause pump seizure. This needs to be confirmed by experiments. (author)