Limit load analysis and safety assessment of an elbow with a circumferential crack under a bending moment

Abstract

The use of the leak-before-break concept in the design of a Primary Heat Transport (PHT) piping system for nuclear power plants requires postulation of the largest credible flaws at highly stressed points and demonstration of system stability under the most severe loading conditions. In the PHT piping system, the elbows and branch tees are normally found to be among the most highly stressed piping components. This necessitates detailed flaw evaluation of these components. In the present paper, safety assessment of a pump discharge elbow of 500 MWe Indian PHWR with a throughwall circumferential crack under a bending moment is carried out using the R6 approach. The stress intensity factors (SIF) have been computed by using a database of SIF for elbows with cracks which was generated in one of our recent studies. Limit loads at plastic collapse have been evaluated by carrying out non-linear finite element analysis. Finally, the safety assessment of the pump discharge elbow is performed by doing a sensitivity study on crack length, applied moment and material fracture toughness.