Design and Fatigue Life Evaluation of Components of Nuclear Steam Generator

Abstract

Steam generator is a shell and tube type heat exchanger use for generating steam in nuclear power plant to generate electricity. In nuclear power plant, each reactor is connected with 4, 700 MWe steam generators. Nowadays, Pressurised heavy water reactor steam generators are used to generate steam at high temperature and high pressure. Steam generated at high temperature and pressure is used to run turbine. Turbine turns generator to produce electricity. Nuclear steam generator is subjected to various loadings and transient cycles during service. So it is necessary to ensure uninterrupted operation of steam generator due to different transient cycles and external loads. So evaluation of steam generator for different fatigue cycles with external nozzle local load is to be carry out theoretically and analytically. ASME section 3 NB provides guidelines for design of nuclear facility components. So design by rule is done by ASME section 3 NB. Theoretically cumulative fatigue usage is found from ASME section 3 NB. Cumulative usage factor should be less than 1 for safe design. Thermal transient cycles provided by customer is used to find change in pressure and temperature with respect to time for different transient loops which will be used as an input for thermal transient analysis in finite element analysis. Various piping local loads acts on nozzles and it is necessary to evaluate effect of these local loads with respect to time, temperature and pressure. Finite element analysis is used to find critical locations and maximum values of stress in critical sections. Linearized stress intensity is determined across most critical section to find stress across thickness. Different load cases are created and combined to find actual stress intensity for different operating cycles and then ASME section 3 NB is used to find cumulative usage factor.