Overview of Code Case on Alternative Design Methodology by Using Elastic-Plastic Finite Element Analysis for Class 1 Vessels in the JSME Rules on Design and Construction

Abstract

An alternative design methodology by using elastic-plastic finite element analysis has been developed and published as a code case of the JSME Rules on Design and Construction for Nuclear Power Plants (The First Part: Light Water Reactor Structural Design Standard). This code case applies elastic-plastic analysis to evaluation of such failure modes as plastic collapse, shakedown, thermal ratchet and fatigue. Advantages of this evaluation method are no use of stress linearization/classification, consistent use of Mises equivalent stress and applicability to complex 3-dimentional structures which are hard to be treated by the conventional stress classification method. The evaluation method for plastic collapse consists of the Lower Bound Approach Method, Twice-Elastic-Slope Method and Elastic Compensation Method. Cyclic Yield Area (CYA) criterion based on elastic analysis is applied to screening evaluation of shakedown limit instead of secondary stress evaluation, and elastic-plastic analysis is performed when the CYA screening criterion is not satisfied. Strain concentration factors can be directly calculated based on elastic-plastic analysis.