Demonstration of Leak-Before-Break in Japan sodium cooled fast reactor (JSFR) pipes

Wakai, Takashi ; Machida, Hideo*; Yoshida, Shinji*; Xu, Y.*; Tsukimori, Kazuyuki

This paper describes the Leak-Before-Break (LBB) assessment procedure applicable to Japan Sodium cooled Fast Reactor (JSFR) pipes made of modified 9Cr-1Mo steel. For the sodium pipes of JSFR, the continuous leak monitoring will be adopted as an alternative to a volumetric test of the weld joints under conditions that satisfy LBB. Firstly, a LBB assessment flowchart eliminating uncertainty resulted from small scale leakage, such as self plugging phenomenon and influence of crack surface roughness on leak rate, was proposed. Secondly, a rational unstable fracture assessment technique, taking the compliance changing with crack extension into account, was also proposed. Thirdly, a Crack Opening Displacement (COD) assessment technique was developed, because COD assessment method applicable to JSFR pipes - thin wall and small work hardening material - had not been proposed yet. In addition, fracture toughness tests were performed using compact tension (CT) specimens to obtain the fracture toughness, JIC, and the crack growth resistance (J-R) curve at elevated temperature. Finally, by using the flowchart, proposed techniques and collected data, LBB assessment for the primary sodium pipes of JSFR was conducted. As a result, LBB aspect was successfully demonstrated with sufficient margins.