A code development for leak before break (LBB) leakage from supercritical to subcritical conditions

Abstract

The leak before break (LBB) concept plays an important role in reactor safety. A code (LEABLE) for leak before break (LBB) leakage estimation was developed in this paper. Complicated crack morphologies and different conditions were taken into account, covering subcritical and supercritical fluids, single phase and multi-phases, choked and unchoked flow. Precise and reliable criteria were proposed for proper model selection. A modified two-phase critical flow model was presented and a single-phase critical flow model for superheat gas was established. Besides, modifications on flashing inception, flow resistance and particulate plugging were conducted in the LEABLE code. Moreover, the code was validated and verified by experimental data for both artificial and natural cracks. Reasonable agreements between experiment values and code predictions are shown for all the conditions. And in the present study the LEABLE shows a higher precision than existing models and commercial softwares (PICEP and SQUIRT). The parameter sensitivity study of LBB leakage was performed as well. The mass flux increases with crack opening crack opening displacement (COD), crack length and the entrance resistance coefficient, and decreases with global and local roughness, number and angle of turns. However, the entrance resistance coefficient and local roughness have limited effects on LBB leakage.