Development of modified piping evaluation diagram for leak-before-break application to Korean next generation reactor

Recently, the piping evaluation diagram (PED) is accepted in nuclear industry for an efficient application of leak-before-break (LBB) concept to piping system at an initial piping design stage. The objective of this paper is to develop the modified PED, which can account for the variation of the material properties of the PED development stage and those of the assembly stage. For this purpose, a parametric study was performed to investigate the effect of stress-strain curve on the detectable leakage crack length and the effect of fracture resistance curve on the LBB allowable load. Finite element analyses were also performed to investigate the effect of stress-strain curve on the LBB allowable load. Finally, a modified PED was proposed as a function of crack length and the allowable safe shutdown earthquake load. The LBB analyses based on the modified PED are in good agreement with those based on the traditional PED. By adopting the modified PED, the variation of material properties can be considered in the LBB analysis and the computing times required for the application of LBB during the design process can be considerably reduced. (orig.)