Final Report on CFD and Thermal-Mechanical Stress Analysis of PWR Surge Line under Transient Condition Thermal Stratification and an Evolutionary Cyclic Plasticity Based Transformative Fatigue Evaluation Approach without Using S~N Curve: Rev. 1

Abstract

This report presents an evolutionary cyclic plasticity based transformative approach for fatigue evaluation of safety critical components. This approach is generic which can be used not only for the present generation light water reactor components (which is our focus) but also for advanced reactor components. The approach is based on the fundamental concept of time-evolution of progressive fatigue damage rather than the end-of-life data based conventional S~N curve approaches. Series of fatigue tests on 316 stainless steel uniaxial specimens were conducted under strain-controlled and stress-controlled cyclic loading in two different environment such as in-air at 300 °C and PWR coolant water condition at 300 °C. Material models are developed to capture the uniaxial test data and are subsequently programmed into commercially available ABAQUS code to transform the uniaxial material behavior to multiaxial loading domain. The developed evolutionary cyclic-plasticity approach is verified by both analytical and 3D-FE modeling of uniaxial fatigue test specimens. Results show that the developed material models can capture the time-dependence of material hardening and softening with great accuracy. In addition, results show that the material models not only can capture the material behavior under constant amplitude loading but also can capture the load-sequence effect under variable and random amplitude loading. The ANL developed approach is one of its kind, which shows first in the fatigue research community that fatigue evaluation of a component (in our case verified for laboratory scale fatigue test specimens with great accuracy) can be performed for its entire fatigue life, including the hardening and softening behavior, without using a conventional S~N curve based approach.

A Deterministic and Probabilistic Framework for Forecasting of Time-Series Damage States and Associated End-of-lIfe of a Pressurizer Water Reactor Surge Line under Design-Basis and Grid-Load-Following Loading Conditions

“…While the rules and practices help prevent thermal stresses, they cannot completely eliminate thermal stresses, which over the life of a reactor may become significant. In the Argonne report on CFD analysis of thermal-mechanical stresses under transient conditions, the authors show that the stresses incurred during thermal stratification related transient cases can be significant [4].…”

“…As design life of NPPs is being extended, it is important to investigate the long-term effects that thermal stratification has on the safety of pressurizer surge lines and other similar components subjected to thermal stratification. Thermal stratification has been studied and reported extensively in the literature [4][5][6][7][8][9][10][11][12][13][14][15]. One common approach to studying this and related phenomena is to use a finite element code.…”

“…For the stainless steel pipe, the temperature-dependent properties of specific heat capacity and thermal conductivity were used and can be found in Ref. [4]. Additionally, the density of the pipe metal was taken to be a constant value of 8238 kg/m 3 .…”

“…The structural analyses were performed for elastic and elastic-plastic material properties. To compare the structural analysis results with isothermal fatigue test (at 300 o C) results, we used the isothermal material properties at 300 o C. The associated material properties can be found in Table 5.1 and in our earlier publication [4]. For the heat transfer analysis, we used the temperature-dependent material properties that can be found in [4].…”

“…We validated our CFD modeling strategy in section 2 for a transient experimental loading case. In our earlier publication [4], we had discussed the CFD results for the SL pipe shown in Figure 3.2 for different transient cases. However, the full fuel cycle CFD model of the SL pipe is still under development.…”