LBB assessment on ferrite piping structure of large-scale FBR

These days, the interest on LBB (Leak Before Break) design becomes to be rising in the viewpoint of the cost reduction and structural integrity for the commercialization of FBR plants. LBB design enables plants to be shut down safely before occurring unstable fracture by detecting the leak rates even if a crack initiates and penetrates a wall thickness. It is necessary to assess crack growth and penetration behavior considering in-service conditions under operation temperature, leak rates considering the detector capability and unstable fracture quantitatively for LBB assessment. The governing service loading of FBR can be identified thermal expansion stress and thermal transient stress because the operation temperature is higher than that of LWR and the liquid metals contain higher heat transfer coefficient than water. On that reason, the use of 12Cr type ferrite steel in the primary cooling system is investigated for reducing stress in the design of large-scale FBR. This study deals with LBB assessment when the primary piping components of FBR which consist of 12Cr type ferrite steel are subjected to a series of transients, and the results envisioned the use of 12Cr type ferrite steel for FBR components. (author)