| dc.description | This paper presents a study of the application of Leak-Before-
Break (LBB) to nuclear piping using three different materials. Although had
been introduced more than three decades ago, through a fundamentally
technical justification, the LBB concept currently has been widely applied in
nuclear installations projects in several countries. Based on the fracture
mechanics, the LBB concept considers that a leakage from a crack can be
detected before it reaches a critical size that implies the pipe failure, that is,
the LBB analysis demonstrates through a technical justification that the
probability of pipe rupture is extremely low. Among the aspects that involve
the application of LBB, the main ones are: the definition of the material
properties, which are obtained through tensile and fracture tests; the leakage
analysis, which determines the rate of leakage due to the presence of a
through-wall crack; and the analysis that verifies if the crack is stable
considering the failure modes by ductile tear and plastic collapse. The
materials SA-508 Cl. 3, SA-106 Gr. B and SA-376-TP304 were evaluated in
relation to their performances for LBB. Data obtained from literature cases
were used for the materials properties, and for the geometry and loadings of
the pipe, all corresponding to the primary circuit of a PWR reactor. After
application of the LBB, it was verified that all three materials met the limits
established in the methodology. SA-508 Cl. 3 and SA-376-TP304 steels
showed the best performance for ductile tear failure and plastic collapse
failure, respectively, and SA-106 Gr. B steel had the lowest performance in
both. All three materials presented plastic collapse as the most likely failure
mode. In general, SA-376-TP304 steel presented the best performance for the
LBB among the three materials evaluated in this work. | |
