Structural integrity assessment of a nuclear vessel with FITNET FFS and Master Curve approach

The structural integrity of a Spanish nuclear vessel was assessed by obtaining the operation pressure–temperature (P–T) limit curves relevant to the beltline region according to the ASME Code. This method requires the knowledge of the material fracture toughness in the ductile to brittle transition (DBT) region which is conventionally described by the semi-empirical reference temperature RTNDT. Recent development of the Master Curve (MC) methodology, with T0 as a reference temperature, is an attractive alternative that do not rely on empirical correlations. Thus, the P–T curves were also calculated according to the N-629 and N-631 ASME Code Cases which partially include T0 through RTT0RTT0. Finally, to evaluate the conservatism of the different methodologies (ASME Code and Code Cases), the analysis was performed by means of the FITNET FFS procedure that consistently incorporates the MC concepts. The study demonstrates the conservatism of the ASME code which is manly due to the definition of the semi-empirical RTNDT index.