Larger-diameter cylindrical vessels for commercial fast breeder reactors (FBRs) are planned to increase the electric generation capacity with thinner vessels compared to the existing ones. The modified 9Cr-1Mo steel (ASME Grade 91 steel) has high yield stress and low tangent modulus after yielding, and plans to be applied as well as austenitic stainless steel for vessels in existing FBR power plants. Although elasto-plastic axial compression, bending and shear buckling are expected to occur in vessels, the current buckling strength evaluation from the Japan Society of Mechanical Engineers (JSME) standard “Design and Construction for Nuclear Power Plants, Division 2 Fast Reactors” mainly focuses on plastic buckling of thick cylindrical vessels.
Seismic base isolation is being devised for next-generation FBR power plants by the increasing seismic design load in Japan. When a horizontal seismic base isolation design is adopted, cylindrical vessels are subject to cyclic vertical seismic load with long-period horizontal seismic wave. The deformation by cyclic vertical load reduces the buckling strength.
In this paper, we modified the existing buckling strength equations focusing on elasto-plastic axial compression, bending and shear buckling under cyclic axial load (hereinafter called “modified equations”), and confirmed their applicability through a series of elasto-plastic buckling analyses. We also conducted a series of buckling tests on Grade 91 steel vessels in the load regions where axial compression, bending and shear buckling interact, and where axial compression and bending buckling are dominant due to large vertical load. The buckling behavior and the buckling load estimated by the elasto-plastic buckling analysis considering the actual material stress–strain relationship and imperfections in the test vessel suitably agreed with corresponding test results in the load regions.