Development of the Buckling Evaluation Method for Thick Cylindrical Vessels With a Conical Section in Fast Reactors Made of Austenitic Stainless Steel

Abstract In commercial fast reactor (FR) power plants in Japan, a seismic isolation system is expected to be adopted in the next generation of fast reactors to cope with the relative thinning of the reactor vessel due to the enlargement of the diameter and the increase of the design seismic motion. It is assumed that elastic-plastic axial compressive buckling, bending buckling, and shear buckling are superimposed on a large-diameter cylindrical vessel. However, it is difficult to properly evaluate these complicated elastic-plastic buckling modes in the current rules for prevention of buckling in “Codes for Nuclear Power Generation Facilities, Rules on Design and Construction for Nuclear Power Plants, Section II Fast Reactor Codes” of the Japan Society of Mechanical Engineers (JSME). Therefore, the authors proposed a buckling evaluation method for the cylinder structure in the previous study 12. On the other hand, the intermediate heat exchanger (IHX) and safety vessel in the demonstration reactor under design study in Japan are supposed to be designed a structure with a conical section as a transition member between cylinders with different diameters. However, the effect of the conical section on the buckling strength is not considered in both the current rules in the JSME and the proposed buckling evaluation method for cylinder structure. In this study, buckling mode and buckling load were confirmed by buckling tests of a cylindrical structure with conical section, and a buckling evaluation equation considering the effect of conical section was also examined. The buckling test was performed under horizontal load on a test specimen with conical section, assuming IHX as a long and thick cylindrical structure. The buckling evaluation method was applied by converting the radius, thickness, and angle of a conical section into an equivalent cylinder, which is adopted in the buckling evaluation method for the conical section in the AEME/BPVC Code Case N-759. These results showed that the buckling load obtained in the test could be evaluated conservatively. In addition, elastic-plastic buckling analyses were performed considering the initial imperfection shape and the stress-strain relationship of the test vessel. The results of the analyses confirmed that the prediction accuracy of the buckling load was within 10% of the buckling strength obtained in the test, and the buckling mode and load could be simulated with good accuracy.