Proposal of the buckling design method by elasto-plastic buckling analysis for steel containment vessel of nuclear power plant

One of the seismic design methods for the steel containment vessel (SCV) of nuclear power plant is established by the Japan Electric Association as JEAC 4601-2015: Technical code for aseismic design of nuclear power plants. The buckling evaluation formulas for SCV in JEAC 4601-2015 are based on a number of buckling test results of various cylinders conducted by NASA (National Aeronautics and Space Administration)(1968) and considered a safety margin. The SCV shall be designed simply and conservatively using the formulas. Recently, the buckling evaluation method using static elasto-plastic buckling analysis has been studied and applied to vessel structures, such as the reactor vessel in fast breeder reactor plant. The elasto-plastic buckling analysis can consider seismic load distributions, openings, initial imperfection of vessel and stress-strain relationship directly in the analysis model, and can evaluate the buckling behavior and buckling load more realistically and reasonably compared to the design formulas. However, the buckling loads calculated by the elasto-plastic analysis are strongly affected by the analysis condition such as material properties, mesh size and initial imperfection shape, and it might be overestimated. In this study, the elasto-plastic buckling analyses for the buckling test of steel cylindrical vessel corresponding to the dimensions of SCV were carried out in various analysis conditions to confirm the sensitivity of buckling load and to establish the analysis procedure and the analysis conditions that can calculate the buckling behavior and buckling load of SCV conservatively and rationally. In addition, to verify the effectiveness of the proposed buckling design method by analysis, the elasto-plastic analyses in accordance with it were conducted for a series of buckling tests of steel vessels with or without stiffening rings. As a result of these analyses, the applicability of the proposed buckling design method by analysis was confirmed.