The accelerator-driven nuclear transmutation system aims at transmuting minor actinides (MAs) and long-lived fission products to stable or short-lived nuclei. A feasibility design study of the proton beam window, which is an interface component between an accelerator and a nuclear reactor, needs a method to be able to evaluate heat transfer characteristics of the beam window under flowing lead bismuth. However, the validity of the numerical simulation model of the beam window has not been proven yet and a database on heat transfer characteristics has also not been established. Two experiments were conducted: one was particle image velocimetry measurement around the beam window in flowing water and the other was temperature measurement at the beam window under flowing lead bismuth. Numerical simulation was also done to validate the beam window model for design work. Results show that heat transfer characteristics of the beam window averaged in space and time under flowing lead bismuth was formulized by the experimental equation. The numerical simulation model can estimate the mean heat transfer coefficient. However, the local heat transfer coefficient was not stable: it fluctuates with time and even in space, especially around the stagnation point. The reason is discussed in detail.
