A new plastic correction for the stress intensity factor of an under-clad defect in a PWR vessel subjected to a pressurised thermal shock

For the assessment of an under-clad defect in a vessel subjected to a cold pressurised thermal shock, plasticity is considered through the amplification β of the elastic stress intensity factor K_I in the ferritic part of the vessel. An important effort has been made recently by CEA to improve the analytical tools in the frame of R&D activities funded by IRSN. The current solution in the French RSE-M code has been developed from fitted F.E. calculation results. A more physical solution is proposed in this paper. This takes into account two phenomena: the amplification of the elastic K_I due to plasticity in the cladding and a plastic zone size correction in the ferritic part.