The Nuclear Research reactor with light water as a coolant has a cooling system equipped with a delay chamber component. The delay chamber function is to reduce the light water flow which gives time for active nuclides such as Nitrogen-16 (N-16) to decay at the permissible threshold. The specification document states a minimum residence time inside the delay chamber is 50 seconds. However, it is necessary to do experimental related to the residence time as a comparison value as well as evaluation for validation. Numerical analysis using computations fluid dynamics (CFD) with scaling models has been carried out. The scale model simulation results show a residence time of 15.6 seconds, which the result will be validated using the Ishi-Kataoka method to scale up the value and obtained an error of 10.09%.