Leak-Before-Break methodology applied to different piping materials: a performance evaluation

Israel Gleybson Ferreira Da Silva,Arnaldo Homobono Paes De Andrade,Waldemar Alfredo Monteiro

doi:10.3221/igf-esis.50.06

Abstract

This paper presents a study of the application of Leak-Before-Break (LBB) to nuclear piping using three different materials. 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 extracted 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 extracted 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 obtained the best performance for the LBB among the three materials evaluated in this work.

Highlights

Nuclear power plants use nuclear fission as a source of heat for energy production
Because they are built using ductile materials, this evaluation is made through the concepts of Elastic-Plastic Fracture Mechanics (EPFM)
AEvaluated materials mong the materials that have been used as base metal in primary circuits piping of PWR reactor SA-508 Cl. 3, SA-106 Gr

Summary

Introduction

Nuclear power plants use nuclear fission as a source of heat for energy production. Currently, 450 nuclear reactors are in operation in the world, producing about 400 GW of electrical capacity; of these units in operation, 298 are PWR (Pressurized Water Reactor). The operating principle of a PWR nuclear plant is based on the removal of heat from the reactor core through a closed circuit of high pressure water, called the primary circuit. The water heated under high pressure in the primary circuit passes through a steam generator where it heats and turns into steam the water of the secondary circuit. This steam moves a turbine that drives an electric generator. A crack in the piping should cause a leakage in a considerable amount, allowing its identification and quantification, before a growth can occur that would lead to a sudden rupture of the pipe This is the essence of the Leak-Before-Break (LBB) concept. Through a fundamentally technical justification, the LBB concept has been widely applied in nuclear installation projects in several countries [2, 3, 4, 5]

Methods

Results

Conclusion