Leakage assessment in leak-before-break analysis

The assessment of a leakage event in an operating nuclear power plan requires a profound knowledge of structural and fluid mechanical phenomena. One relevant situation is the leak-before-break analysis, which analyzes if a leakage can be found while it is small and controllable, which prevents a rupture. The elements of such a detectability analysis require the computation of flow rates through narrow cracks as well the assessment of the stability of flawed pipes. For this purpose, the codes WinLeck and PROST have been developed by GRS. These codes include multiple model approaches, which are useful for the systematic evaluation of laboratory measurements, since modelling effects and other influences can be separated. These codes allow also the processing of a matrix of test cases, which is done in the form of a sensitivity study. Relevant influence quantities for the leak-before-break characteristics turn out to be the pipe size, the friction factor due to the roughness of the leakage path boundaries, the material's yield stress, the fracture toughness and the detection threshold of the leakage monitoring system.