Study on seismic safety evaluation of crossover pipeline connecting containment and turbine building in three-dimensional isolated nuclear power plant

Abstract

Isolation design enhances the safety of nuclear islands during earthquakes. Magnification of isolation layer displacement increases the damage risk of the nuclear pipeline crossing the isolation gap. A simplified safety evaluation procedure for pipelines based on elbow displacement limits and damage indices was proposed. An analytical model of the nuclear elbow was first developed for unidirectional and multi-directional displacement loading. The failure point is determined based on the elbow force–displacement curve and adjusted to obtain a safe displacement limit. Subsequently, a 3DBNL model with a horizontal isolation frequency of 0.5 Hz and a vertical isolation frequency of 1.25 Hz was proposed based on the BNL model. Nonlinear time history analysis was performed to obtain the dynamic responses such as nuclear island acceleration, isolation layer displacement, and pipe relative displacement. Finally, the damage index was calculated as the ratio of the peak relative displacement to the elbow displacement limit. The damage index and the distribution interval under multi-directional seismic input were calculated separately to assess pipeline safety. The results indicate that the three-dimensional isolated nuclear island remains safe under the horizontal 0.6 g and vertical 0.4 g seismic input, while the pipeline failed under the horizontal 0.3 g and vertical 0.2 g seismic input.