Abstract
There are a lot of types of branch pipes with a closed end in a nuclear power plant. At a branch pipe connected to a main such as a main coolant pipe, there is temperature gradient in the layer between the cavity flow and the colder fluid by heat removal. It is necessary to evaluate the structural integrity of a pipe in the front of the cavity flow and to establish the piping design standard. In the piping design standard, there are the maximum penetration length (L_1) and the minimum one (L_2) in order to avoid the elbow between L_2 and L_1. The L_1 evaluation method is shown in the present report. The method is based on the momentum balance model by defining the boundary layer coefficient. The method reproduced the penetration length by cavity flow in several types of the vertical pipes within 10% accuracy. The piping design standard is going to be established by using the method.
