[en] The methods of removing impurities in the liquid sodium for FBR and the methods of measuring the concentration of impurities are reviewed. The coexistence of liquid sodium with austenite stainless steel now in use for FBR is also reviewed. Cold traps or hot traps are equipped in bypasses in loop type Na equipments in order to continuously remove impurities in sodium, and sodium is handled in inert gas atmosphere to prevent mixing of impurities. The methods of measuring concentration are chemical analysis, electrochemical analysis, distributive equilibrium method, and C and H diffusion gas analysis process. The distributive equilibrium method is that utilizing distribution of nonmetallic elements between liquid sodium and solid metals. An example of the coexistence experiment of sodium at high temperature and at high flow rate is reviewed. An example of corrosion model in high temperature, high speed sodium is also reviewed. As an example, Westinghouse sodium loop for testing material is illustrated. Further, the corrosion model between iron and sodium in boundary layer by Weeks is illustrated. The corrosion rate Rsub(ss) of stainless steel can be computed by the equation Rsub(ss)=(7.93 x 10¹¹T/Xsub(Fe)) [C₀(Na)/C₀⁰(Na)]sup(2XFe) exp(-50,300/RT) (1-5 x 10^-5(L/D)²) mil/year at 650-760⁰C in the range of 3-30 ppm C₀(Na), in which (Na) is dissolved state of oxygen in sodium. (Iwakiri, K.)