Simplified Elastic-Plastic Analysis Methods in the JSME Rules on Design and Construction

Abstract

In a fatigue analysis for Class 1 components in the Rules on Design and Construction for Nuclear Power Plants (The First Part : Light Water Reactor Structural Design Standard) in the JSME Codes for Nuclear Power Generation Facilities, a simplified elastic-plastic analysis is used when the primary plus secondary stress intensity exceeds 3 times the Design Stress Intensity. The simplified elastic-plastic analysis is to multiply elastic-analysis-based stress by a Ke-factor. It is well-known that the Ke-factor of the ASME Boiler and Pressure Vessel Code Section III has a large amount of conservatism. Hence, to develop an appropriate Ke-factor evaluation method, the Ke-factor Advisory Committee was established in June 1999 as a research committee of the Thermal and Nuclear Power Energy Society. Typical basic models were selected from actual structures. Elastic analyses and elastic-perfectly plastic analyses were performed for the basic models and the Ke-factors were calculated. equations were established by bounding the Ke-factors. The new equation was verified by using experimental data of piping. The factors for typical actual nozzles of which Ke-factors were relatively higher were directly analyzed and it was confirmed that the developed evaluation method could be higher than the Ke-factor directly analyzed. Based on those evaluations, the Ke' equation expressed by Primary + Secondary Stress Intensity (Sn) and the Ke equation expressed by Primary + Secondary + Peak Stress Intensity (Sp) were developed. The Ke' equation has been taken in the JSME Design and Construction Code and the Ke equation has been taken in the Code Case, Alternative Structural Evaluation Criteria for Class 1 Vessels based on Elastic-Plastic Finite Element Analysis.