Session: CS-12-01 High Temperature Codes and Standards

Paper Number: 123103

123103 - Development of the Buckling Evaluation Method for Large Scale Vessels in Fast Reactors Made of Grade 91 Steel and Austenitic Stainless Steel With Large Initial Imperfections 

Larger-diameter cylindrical vessels, because of their capacity enlargement, are pursued in response to the demand for economic competitiveness of commercial fast reactors (FRs). To accommodate the thinner vessel accompanied with larger diameter and the increasing seismic design load in Japan, the seismic base isolation is being planned for the application to FRs power plants. When a horizontal seismic base isolation design is adopted, cylindrical vessels are subject to cyclic vertical seismic load with long-period horizontal seismic load. Since the deformation generated by cyclic vertical load reduces the buckling strength, the effect should be taken into account. Although superposition of elastic-plastic axial compression, bending and shear buckling are expected in the larger-diameter cylindrical vessels, the current rules of buckling limit in the Japan Society of Mechanical Engineers (JSME) standard “Design and Construction for Nuclear Power Plants, Division 2 Fast Reactors” cannot estimate these complex elastic-plastic buckling modes adequately.
Therefore, we proposed the modified buckling strength evaluation method focusing superposition of elastic-plastic axial compression, bending and shear buckling under cyclic axial load, and evaluated their applicability through the buckling tests and analyses under monotonic or cyclic axial compressive load accompanied with constant horizontal load in the previous studies. The experiment and simulation results have confirmed the conservatism of the modified equations to Grade 91 steel and austenitic stainless steel vessels with circumferential wrinkle shape corresponding to the elephant foot buckling mode as a significant initial imperfection, under the dominant cyclic axial compressive load accompanied with horizontal load.
In the most of tests and analyses in previous studies, the amplitude of the initial imperfections of vessels were less than or equal to half the wall thickness. However, depending on the fabrication method, the initial imperfection of the large scale vessels might be larger than that. Therefore, we proposed a correction factor to reduce the buckling strength calculated by the modified equations for large initial imperfections.
In this study, a series of elastic–plastic buckling analyses considering large displacement and large strain theories was conducted to Grade 91 steel and austenitic stainless steel vessels which has a wide range of dimensions, initial imperfection amplitude, and vertical/horizontal load ratio. The simulation results have shown that the correction factor generally shows a reduction tendency of buckling strength corresponding to initial imperfection amplitude, and the modified equations are applicable to the vessels in FRs power plant even for large initial imperfection amplitude which exceeds half the wall thickness.

Presenting Author: Kazuhiro Miura Mitsubishi Heavy Industries, LTD.

Presenting Author Biography: Working for Mitsubishi Heavy Industries in Strength Laboratory, Research & Innovation Center as Senior Deputy Manager.
Addressing buckling strength for 10 years.

Authors:

Takashi Okafuji Mitsubishi Heavy Industries, LTD.
Kazuhiro Miura Mitsubishi Heavy Industries, LTD.
Hiromi Sago Mitsubishi Heavy Industries, LTD.
Hisatomo Murakami Mitsubishi FBR Systems, Inc.
Tomoyoshi Watakabe Japan Atomic Energy Agency
Masanori Ando Japan Atomic Energy Agency
Masashi Miyazaki Japan Atomic Energy Agency