Materials and NDE aspects in the RPV operating conditions behaviour

The demonstration of the in-service resistance of the PWR vessels is based on the toughness evaluation of the materials constituting the vessels. The objective is indeed to compare the toughness to the solicitations applied on a crack, resulting from the different loading potentially experienced by the component. This article aims at presenting the in-service inspections - NDE aspects - as well as the toughness assessment method, closely linked with different materials aspects. The potential defects in the welded, cladded shells of the PWR vessels are only fabrication flaws. To date every core zone vessel has been entirely examined by a non destructive process. The implemented Ultrasonic Techniques are qualified according to the RSEM code since 1999. Thus, EDF has a reliable and exhaustive knowledge of the manufacturing defects to be found under the cladding of the PWR vessel core zones. The toughness of the materials is determined according to an indirect method. It is based on a codified lower bound curve associating the minimum KIC to a reference temperature, the RTNDT. RTNDT is characteristic for a material and integrates the evolutions due to neutronic bombardment through specific irradiation formulae. The Pressure Vessel Surveillance Program allows to verify that the formulae are conservative. The PVSP results and an analysis of the toughness assessment are presented in this paper. (authors)