Sodium (Na) has been used as the coolant of fast reactors for the various merits. On the other hand, it is postulated that steel liner may fail and lead to sodium-concrete reaction (SCR) during the Na-leak accident. Because of release of hydrogen gas due to the chemical reactions between Na and concrete components, SCR is one of the important phenomena in the Na-leak accident.
　In this study, fundamental experiments related to SCR were performed using Na and concrete powder. The used concrete powder is milled siliceous concrete which is used as the structural concrete in Japanese nuclear power plants. The obvious temperature changes around 100, 300 and 500 ℃ were observed for Na-melt, NaOH-SiO₂ and Na-H₂O-SiO₂ reaction, respectively. Especially, the violent reaction around 500 ℃ caused the temperature peak to 836~853 ℃, and the reaction heat of 0.15 ~ 0.23 kW g^-1 was estimated under the Na-concrete mixing ratio such as Na concentration, γ ≈0.32.
　After the experiments, main components and thermophysical properties of the reaction products were measured. The main component was identified as Na₂SiO₃ with X-ray diffraction technique. The measured thermophysical properties of melting point, density, specific heat, thermal conductivity and viscosity were similar to those of xNa₂O-(1-x)SiO₂ (x ≦ 0.5).