To protect the first wall of an inertia fusion reactor from extremely high heat flux. X-rays, alpha particles and fuel debris caused by a nuclear fusion reaction, a "cascade-type" failing liquid-film flow is proposed as a "liquid-wall" concept. The flow visualization experiment to investigate the feasibility of this liquid-wall concept has been conducted. The preliminary numerical simulation results suggest that the current cascade structure design should be improved because less thermal-mixing is expected. The cascade-type structure has, therefore, been redesigned. This new cascade-type first wall consists of a liquid reservoir which has a free-surface to maintain a constant water head in the rear, and connects to a slit composed of two plates, i.e., the first wall is connected to a slit which is partially made up of the first wall to begin with The numerical simulations were performed on the new cascade-type first wall and they show the stable it. liquid-film flow on it. Moreover, the POP (proof-of-principle) flow visualization experiments, which satisfy the Weber number coincident condition, are carried out using water as the working fluid. By comparing the numerical and experimental results. it was found that the liquid-film flow with 3-5 mm thickness could be stably established. According to these results for the new cascade-type first wall concept, it was confirmed that the coolant flow rate and the thickness of the liquid-film could be controlled if the Weber number coincident condition was satisfied. (C) 2008 Elsevier B.V. All rights reserved.