Shigehiro Shimoyashiki

Investigation of self-welding rate of structural materials in liquid sodium

The characteristics of self-welding of fast breeder reactor structural materials in liquid sodium have been investigated. A maximum contact pressure of 98 MPa was loaded on the materials (Type 304, Type 321, Inconel 718, and 2.25 Cr-1 Mo steel) for 100 to 900 h in sodium at 505 to 550/sup 0/C. Shear stress for breakaway between the bonded material couples is in proportion to contact pressure. The 2.25 Cr-1 Mo steel welded to itself is the strongest combination among couples of the same material. Each pair of two materials chosen from Type 304, Type 321, and Inconel 718 materials shows almost the same self-welding coefficient, which is defined as the ratio between shear stress for breakaway and contact pressure on testing. Self-welding coefficients are in proportion to the square root of the contact periods and increase as the temperature of sodium is elevated. The apparent activation energy obtained from the self-welding coefficient is -- 188 kJ/mol for the combination of 2.25 Cr-1 Mo/2.25 Cr-1 Mo, and 218 kJ/mol for Type 304 or Type 304/Type 321.