With the life extension of Nuclear Power Plants worldwide, new challenges have emerged in engineering calculations. These challenges often stem from the difficulty to demonstrate an adequate margin for some key components, which have gradually been ageing during the operation of the plant. In particular, the Reactor Pressure Vessel (RPV) is impacted by the irradiation, and the risk of brittle fracture under severe cold shocks must be assessed.
In parallel to conventional approaches, a significant amount work has been performed over the past 20 years in France to adapt the historic Griffith energy release-rate approach to engineering space. The work was initiated by Francfort and Marigowho set up a new elastic fracture theory, extended from the Griffith approach. Lorentz and Wadier have since then improved the model which is based on several ingredients including the application of an energy minimization principle, the definition of a specific damage model and the use of a notch to represent the crack.
Among other advantages, the Cleavage brittle fracture energy approach parameter (Gp) method has been developed as a true engineering approach and hence is relatively easy to implement in a FEA software: it has already been implemented into code_aster developed by EDF R&D . Recently, CEA also implemented the method in Cast3M .
Beyond the application in France, and in the wake of a simple comparison benchmark launched in 2018 with CNNC/NPIC from China on a CT specimen , a calculation on a RPV type geometry was initiated. This is the second step of a larger effort aiming at working together on establishing a strong industrial basis to demonstrate applicability in engineering and structural integrity space.
The paper provides the progress achieved in the benchmark work and the results obtained in the frame of the work jointly led with company B in the field.