An advanced seismic analysis of an NPP powerful turbogenerator on an isolation pedestal

This paper presents a detailed seismic analysis of a powerful high-speed Russian turbine within a Nuclear Power Plant. Although dozens of these turbines have worked reliably since the 1970s worldwide, until the last decade, only simplified structural analyses were available due to the turbines’ complicated overall structure and internal design. The current analysis considers the detailed geometry of the turbine itself and the vibration and seismic isolation system within the turbine's pedestal and the full range of operational, accident and seismic loads like high pressure, outside loads induced by pipelines and so on. To solve the problem of the turbine seismic qualification, the following steps have been taken. The first step was to create detailed finite element models of the turbine's high and low pressure parts and rotor system with bearings. Using such models, corresponding simplified models were developed to be included into the coupled model of the system: “Building–Vibroisolation Pedestal–Turbine” (BVT). The second step was the analysis of that coupled system. Soil–structure interaction was considered using actual soil conditions. Three components of time history acceleration were used to define seismic excitation. As the result of BVT system analysis, a full picture of time history displacements and loads was determined. At the same time, a problem of rotor gaps was solved. In the final step, determined loads were applied to the detailed models of the turbine's parts for seismic qualification of the whole structure.