Abstract
Prediction of crack propagation kinetics in the components of nuclear plant primary circuits undergoing Stress Corrosion Cracking (SCC) can be improved by a refinement of the SCC models. One of the steps in the estimation of the time to rupture is the crack propagation criterion. Current models make use of macroscopic measures (e.g. stress, strain) obtained for instance using the Finite Element Method. To go down to the microscopic scale and use local measures, a two-step approach is proposed. First, synthetic microstructures representing the material under specific loadings are simulated, and their quality is validated using statistical measures. Second, the shortest path to rupture in terms of propagation time is computed, and the distribution of those synthetic times to rupture is compared with the time to rupture estimated only from macroscopic values. The first step is realized with the cross-correlation-based simulation (CCSIM), a multipoint simulation algorithm that produces synthetic stochastic fields from a training field. The Earth Mover’s Distance is the metric which allows to assess the quality of the realizations. The computation of shortest paths is realized using Dijkstra’s algorithm. This approach allows to obtain a refinement in the prediction of the kinetics of crack propagation compared to the macroscopic approach. An influence of the loading conditions on the distribution of the computed synthetic times to rupture was observed, which could be reduced through a more robust use of the CCSIM.
Highlights
Stress corrosion cracking (SCC) is a major problem in the nuclear industry
We propose a complementary approach where (i) the microstructure is simulated through the cross-correlation-based simulation (CCSIM) [21,22], a geostatistics-based algorithm and (ii) the kinetics of crack propagation is described as an empirical law that reproduces laboratory observations
The grain structure seems random regarding to the training image, and no specific part could be spotted as being qualified of low quality
Summary
Stress corrosion cracking (SCC) is a major problem in the nuclear industry. It is one of the main environmental degradation phenomena affecting the materials of pressurized water reactors (PWR) [1]. The integrity of primary circuit, where flows the hot primary water (320 ◦C, 150 bar), is at stake since operational feedbacks revealed a potential susceptibility to SCC of various primary materials: austenitic stainless steels [2], nickel based alloys [3,4] and their weld joints [5,6]. SCC mechanisms require the synergistic effects of mechanical, metallurgical and environmental factors [7]. Those effects taken into account individually may not be harsh enough to damage the material, but they jointly can lead to great damages and failure
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