A comprehensive review of the leak flow through micro-cracks (in LBB) for nuclear system: Morphologies and thermal-hydraulic characteristics

Piping cracks are widely spread in the nuclear system, which affects the safety and economy of reactors. The leak before break (LBB) concept detects the leakage through cracks and afterwards takes human intervention, to avoid break and rupture of pipes. Therefore the leakage through crack determines the safety of the reactor second pressure boundary. This paper looks over the existing research on LBB application and focuses on the leak through crack, which largely depends on the crack morphologies and thermal–hydraulic characteristics. The present work categories the cracks in nuclear piping system, where various morphologies are concluded for different cracks. The thermal–hydraulic characteristics of the leak flow through cracks, such as flow resistance, critical flow, thermodynamic non-equilibrium and flow pattern were systematically summarized and reviewed. Besides, the leak experiments were collected for natural and artificial cracks, and the theoretical calculation methods including commercial system software, numerical simulation and interdisciplinary approaches were evaluated. At last, the existing research on the leak flow through crack was summed up and the inherent relationship were clarified. This review paper provides a comprehensive foundation and guidance for the mechanism understanding of leak flow through cracks and LBB application.