Corrosion behavior of the cladding tubes (316SS) for FBR in high temperature sodium (IV); Effect of sodium exposure for 5,000 hours under a temperature gradient on tensile properties of various heats of fuel cladding tubes

not registered; Kano, Shigeki; Nakasuji, Takashi

As the basis for designing and manufacturing the fuel assembly for MONJU, and for confirming its integrity, it has been required to get the data concerning tensile properties of various heats of fuel cladding tubes exposed to different sodium environments. In this report, thirteen heats of fuel cladding tubes containing four kinds of ones manufactured in a few foreign countries were examined. These tubes were exposed to sodium at the linear temperature gradient test section of the Material Test Sodium Loop 1 for about 5000 hours. After that, tension tests of these tubes were made to clarity effects of sudium exposure on these tensile properties. Furthermore, additional tests related to these tensile properties were done. The results obtained are as follows. (1)From comparison of tensile properties before and after sodium exposure of these tubes, yield strength and tensile strength decreased after exposure, and fracture elongation increased. The variation amount of the values on tensile properties depended on exposure temperatures, and it was largest in the case of 500C. (2)The effects of cold-working and grain size on tensile test temperature dependence of tensile properties after exposure to flowing sodium up to 650C were similar to those before exposure in tendency. In respect to the effect of chemical composition, it is considered that minor boron content contributes to enhance the stability of tensile properties for sodium exposure. (3)From comparison of the tensile strength values (yield strength Sy, tensile strength Su) applied for designing the Monju fuel assembly with the present test results after sodium exposure, the experimental values were higher than those uf Sy and Su of annealed SUS316, but lower than those of Sy and Su of 20% cold-worked SUS316. (4)After tension test of sodium exposed tubes within the temperatures of 500C to 650C, many grain boundary cracks in slight depth were round out in the sodium ...