Numerical analyses of a mat below a nuclear power reactor under seismic loading

Abstract

The Nuclear Power Reactor facility is an important and very sensitive nuclear structure due to its requirement to have both structural and radiational integrity for ensuring nuclear safety to the people and environment. The mat foundation of reactor building has to be stable under probable static and seismic loads in compliance with national and international nuclear regulatory requirements. To estimate the deformation of mat foundation under static and seismic loading, it is required to consider the engineering properties of soil beneath the foundation and also the probability of having post-liquefaction settlement. The main goals of the analysis are to determine the anticipated settlement and tilting of mat foundation under Nuclear Power Reactor considering designed static and seismic loads. The mat foundation of the Reactor building is modeled with two different soil conditions, like natural and improved soil using numerical analysis software Plaxis 3D to achieve the goals. In this study, the designed structural and seismic loads are taken from Rooppur Nuclear Power Plant Project and applied on models of mat foundation. Four models are developed considering natural and improved soil in which all designed static and seismic loads are applied using the finite element method Plaxis 3D software. For seismic loads, the Kobe and Loma Prieta earthquakes are used, taking into consideration the scale of maximum designed peak ground acceleration of 0.33 g. Analyzing the unimproved soil model with Koba earthquake, it is observed that the maximum settlement and tilting are 42.36 cm and 0.0036 and with Loma earthquake maximum settlement and tilting are 42.34 cm and 0.0025 respectively. According to Russian code PiNAE-5.10-87 “Rules and Regulation in Nuclear Energy”, the maximum allowable settlement of structural foundation of reactor building is Su  30 cm and the tilting of I-category structure is allowable up to <0.003 in seismic loads. Analyzing the improved soil model, with Koba earthquake the maximum settlement and tilting are found 23.68 cm and 0.0018 and with Loma earthquake maximum settlement and tilting are 23.60 cm and 0.0014 respectively. Numerical analyses shows that engineering soil properties of Rooppur NPP site have drastically change of improved soil and as results decreased settlement and tilting of mat foundation of Nuclear Power Reactor which have the compliance with related regulatory requirements.