Corrosion or fatigue can lead to the formation of cracks in pipes of nuclear power plants. If these cracks penetrate the pipe wall, this, in turn, can lead to leaks through which large amounts of water and steam might escape within a short period of time (see figure below).
How severe the damages caused by such leakage may be depends on the so-called discharge flow rate (also referred to as leakage rate) of the leak. It refers to the amount of steam or water that escapes through the leak per unit of time.
The estimation of this discharge flow rate is important, for example, to assess the loss of coolant, but also to locate a leak in the pipe system. Given the risk that small cracks continue to grow which may result in a pipe rupture, it is important that already small through-wall cracks will be detected by using leak detection systems.
The WinLeck computer program offers a number of simplified models to the user to calculate leak areas and discharge flow rates on the basis of geometry, material and medium (water or steam).
For the calculation of the discharge flow rate, two factors are relevant:
• the size of the crack opening, and
• the flow of fluid through the crack.
For both parameters, there are a number of model approaches in WinLeck, i.e. five leak area models, five leakage rate models, variants of the models, and the possibility to calculate leakage rates by coupling with the ATHLET system code.
Thus, there are different calculation methods available, depending on the application limits of the individual models, to also consider uncertainties in the prediction of leakage rates.