A crack flow rate model for leak-before-break applications

The ability to determine leakage from cracks or flaws is of vital importance in demonstrating the leak-before-break condition. This paper describes a fully continuous analytical model that was developed to predict flow rates through tight cracks in pipes and tubes. The initial blowdown can be subcooled liquid, saturated liquid, two-phase mixture, saturated steam or superheated steam. The model is based on Henry’s homogeneous non-equilibrium critical flow model ( Henry 1970 ) for blowdown of initially subcooled or saturated liquids in frictionless pipes. Extensive modifications were made to account for different initial fluid conditions, surface roughness of the walls, and curved flow paths. The model can be used for calculating flow rates through fatigue or intergranular stress corrosion cracks (IGSCC). Guidelines for selecting the number of crack path changes in direction are provided. Experimental data for flow through tight cracks is scarce. The model has been assessed using several open literature data (includes both fatigue and IGSCC cracks) for all fluid conditions. The work reported here has been used to help resolve leak-before-break issues for PWR and BWR plants.