Gas-lift enhanced natural circulation of alkali and heavy liquid metals for passive cooling of nuclear reactors

Abstract

Gas-lift enhanced natural circulation of alkali and heavy liquid metals is a desirable option for passive cooling of advanced large, small, and micro nuclear reactors, accelerator driven systems, thermal solar plants, and experimental facilities and test loops. The injected inert gas into the riser or the chimney above the reactor core needs to be in the bubbly flow regime for best performance. Gas-heavy liquid metals flow maps are developed based on a well-established theoretical knowledge and the reported experimental data for various test loops. In addition, a thermal-hydraulics model for enhanced natural circulation of heavy liquid metals is developed and validated using the reported experimental data for LBE-N2 and LBE-Ar flow loops. The developed and validated thermal-hydraulics model and two-phase flow maps are used to parametrically investigate natural circulation enhancement of liquid sodium, molten lead, and liquid LBE in a representative loop with Ar gas injection. For enhanced natural circulation of alkali and heavy liquids metals of Na, Pb and LBE, the determined average gas void fraction in the bubbly flow regime is < 0.2. The rates of natural circulation of liquid sodium, molten lead, and liquid LBE increase with increased riser height and/or the gas injection rate for operating in the bubbly flow regime. For the same riser height and gas average void fraction, the natural circulation rates of molten Pb and LBE are similar but much higher than that of liquid sodium. However, liquid sodium has a much higher heat capacity for operating at higher fission power density in or lower temperature rise across the reactor core.