In this study are presented the results of an investigation on the durability of 2.25Cr-1Mo steel in conditions of water-in-sodium small leaks in the range of their initial flow rates, 0.005 ∼ 0.02 g/sec. Water outflow into sodium was performed through an artificial defect, having a cross section diameter of 0.1 ∼ 0.2 mm in the specimen of the steel under investigation, with simulated wall thicknesses of 2.5, 3.5, and 5.0 min. Water injection through the defects was performed at a pressure of 5 ∼ 10 atm (gauge) in sodium flow, having a velocity of ∼0.3 m/sec and temperature of 450 ℃. In six experimental runs, the overall leak quantity of water has been measured. For the walls' thickness investigated in the experiments, the injected water masses have been measured to be in the limits of 25 ∼ 125 g, increasing with the walls' thicknesses. We give the results of a visual and metallographic investigation of the 2.25Cr-1Mo steel specimens in the region of water outflow channel rupture and determination of the final dimensions of the channel. In the steel rupture region, no changes in the steel structure, elemental composition or traces of inter-granular corrosion have been detected.