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Report No.
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Development of LBB assessment method for Japanese Sodium cooled Fast Reactor (JSFR) pipes, 3; Fracture asessment methods considering compliance at a crack part

Wakai, Takashi ; Machida, Hideo*; Yoshida, Shinji*; Enuma, Yasuhiro*; Asayama, Tai 

For sodium pipes of Japanese Sodium cooled Fast Reactor (JSFR), the continuous leak monitoring will be adopted as an alternative of volume examination of welded joints under conditions of satisfying Leak-Before-Break (LBB). Modified 9Cr-1Mo steel with small thermal expansion and good tolerance to high temperature use is adopted to the sodium pipes, and the simplified pipe design will be achieved. While modified 9Cr-1Mo steel has good tolerance to high temperature use, its fracture toughness is low compared with the austenitic stainless steel used for many former FBR pipes. For this reason, a sophisticated LBB assessment is required for the pipes made of modified 9Cr-1Mo steel. This study was performed for expanding the conditions to satisfy LBB with a detailed evaluation of loading conditions used for a fracture assessment. The rational fracture assessment method, evaluating the loading conditions at a crack part considering change of compliance of the piping system by a crack, was proposed. The loading conditions at a crack part are evaluated by an FEM analysis in which the stiffness of a cracked pipe is modeled (1), and marginal crack size is estimated by the 2 parameter method (2). The stiffness of a crack part is evaluated using the marginal crack size and loading condition (3), and the stiffness of the crack part is reflected into the FEM analysis model (4). The detailed LBB evaluation is achieved by repeating from (1) to (4). It became clear that the conditions to satisfy LBB is remarkably expanded to adopt the proposed method compared with the case using the loading without considering change of compliance by a crack.

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