A comprehensive investigation of computational analysis on flow characteristics, stability and safe limits of a supercritical natural circulation loop for different heating power profiles

The Generation IV International Forum (GIF) is a global organization focused on the research and advancement of next-generation nuclear reactor technologies. GIF-IV reactors particularly seek to improve the safety, efficiency, and sustainability of nuclear power, with an emphasis on developing cleaner and more renewable energy sources. Supercritical water reactors (SCWRs) and supercritical water natural circulations (SCWNCL) are one of the most advanced technologies developed by the GIF-IV for cooling the core of nuclear reactors. In this study,a thermal-hydraulic (TH) model has been developed based on the nonlinearly coupled equations of mass, momentum, and energy conservation, with an equation of state which depends on two independent thermodynamic characteristics pressure and enthalpy. The present model is first validated against literature result such as experimental and numerical which showed a good agreement, followed by a grid independence test (GIT) conducted for both steady state and transient conditions to ensure accurate predictions of the SCWNCL. Further, the simulations are carried out to examine loop behavior and ascertain thermal-hydraulic transient instability, along with determining the stable and safe limits of the SCWNCL. Additionally, numerous simulations have been conducted to ascertain the presence of static instability that occurs at extremely low enthalpy. Furthermore, dynamic instability has been seen in the loop at both low and high enthalpy using three different heating profiles like uniform, point and half sinusoidal profiles, resulting in the construction of the marginal stability map. Subsequently, comprehensive simulations have been conducted to forecast heat transfer deterioration within the loop from a material point of view, aiming to ascertain the stable and safe limits of the SCWNCL. Comparative studies have been conducted with and without the consideration of heating structure stability maps, demonstrating that the addition of the structure provides a higher stability zone compared to its absence.