[en] This report describes the out-of-pile test results to study the characteristics of two phase flow that occurs in the testing rigs to be used in the NSRR forced convection tests. In the tests a void generation was simulated by blowing air into the testing rigs assembled equivalently to the ones used in the in-pile forced convection test. Behavior of flow velocity was measured by drag-disc type flowmeters as the functions of initial flow velocity at the testing section and air flow rate blew into the section. Through the tests and the analyses, the following conclusions are obtained; the large flow depressions observed in the previous forced convection tests were caused by the pump cavitation; the prevention of the pump cavitation was achieved by lowering the pump position; the by-pass flow gave the slightest effect on the flow behavior around the fuel. (author)