2, University Lille 1, Lille, , France
In light water reactors (LWR), neutron irradiation is responsible for the embrittlement of the ferritic steels constitutive of the reactor pressure vessel (RPV) stemming from the formation of solute-enriched radiation induced clusters. A deep understanding of the evolution of such cluster population in terms of size and composition is of critical importance in order to assess the macroscopic mechanical properties of RPV steels. To this end, a multi-scale approach has been developed at EDF R&D. Starting from atomistic calculations (usually Density Functional Theory, DFT) unveiling the fundamental interactions between point defects and solute atoms, modeling of the microstructure over time length and dose rate typical of LWR operating conditions is performed via Kinetic Monte Carlo (KMC) or Cluster Dynamics (CD).
In this paper, we will report the main advancements on DFT calculation, kinetic Monte Carlo and Cluster Dynamics for applications to RPV steels carried out in our team at EDF R&D. First, a methodology for thermodynamical calculation allowing for error mitigation in the case of large simulation box calculation has been extended to the case of DFT: it permits to calculate formation entropy of defects inducing large strain fields such as dislocation loops and solute clusters and eventually to foresee the inclusion of temperature effects in KMC calculation. Then, an improved parameterization of the solute-point-defect interaction for complex alloys within KMC has been developed accounting for concentration effects while hybrid Object KMC-Atomistic KMC simulation tool improves the performance of KMC simulation to the point where typical LWR fluences for 40 year operation are accessible. Finally, an explicit model of cluster dynamics for the prototypal dilute Fe-Cu material will be presented, highlighting current challenges in reproducing the dynamics of Cu precipitation with CD and the importance of correct parameterization of the physical model.