Nuclear Fatigue Analysis Codified Design Rules: Comparison of Cyclic Plasticity Effects

Abstract

Large uncertainties exist in fatigue life evaluation using existing elastic stress analysis. The usage factor is obtained by comparison of strain amplitude evaluation on different points of the components and the fatigue S-N curve of the material. This paper will review existing codified rules in major nuclear Codes that are proposed as simplified elastic-plastic analysis of strain amplitude. The different formulas proposed by the different Codes are described with their own background document and compared on typical cases. Methods are based on simplified elastic-plastic approach (elastic analysis plus correction factor) with associated material data. The Code comparison includes nuclear Codes, as ASME Boiler and Pressure Vessel Code Section III, French RCC-M and RCC-MRx and German KTA; Russian PNAEG Code and JSME rules are also considered based on specific English version of the Codes for fatigue rules. Two types of components are concerned by the comparison: vessels and piping systems. All these Codes are proposing different Ke and Kv rules based on different assumption. Finally, a first set of recommendation to perform reference inelastic analysis will be presented to improve existing codes on an harmonized way, associated to analytical recommendations, all material properties needed and criteria to apply this modern methods. This review is mainly done in World Nuclear Association (WNA), Cooperation in Reactor Design Evaluation and Licensing (CORDEL) Working Group, Codes & Standards Task Force.

Study the Cyclic Plasticity Behavior of 508 LAS under Constant, Variable and Grid-Load-Following Loading Cycles for Fatigue Evaluation of PWR Components

“…The present method used for fatigue life evaluation of nuclear power plant components has large uncertainties [1]. This problem is due to the overdependence on approaches that involve empirical fatigue life estimation, such as use of test-based curves of stress/strain versus life (S~N) and Coffin-Manson type empirical relations.…”

“…1 shows that the tensile-test-based properties are not able to capture the shape of the fatigue test data.…”

Tensile and Fatigue Testing and Material Hardening Model Development for 508 LAS Base Metal and 316 SS Similar Metal Weld under In-air and PWR Primary Loop Water Conditions

“…The relevant design codes allow elastic-analysis-based shakedown or ratcheting analysis of nuclear reactor and pressure components to check against progressive damage due to fatigue. However, as reported in literature [4], large uncertainties exist in fatigue life evaluations that use current elastic stress analysis [4]. Theoretically, if stress and strain stay below the elastic limit, no fatigue will occur in the reactor components.…”

“…4) give the incremental multi-axial representation for intra-cycle kinematic hardening stress or back stress. The equivalent uniaxial form can be integrated over a given cycle to estimate the corresponding cycle parameters (…”

“…Figure 4B 4. Linear kinematic hardening constant C1 with respect to number of iteration during parameter estimation using gradient based optimization scheme and using T07 stress-strain data (from elastic limit to 2% true total strain)…”