Alwr thermal hydraulics is the specialized academic and engineering field concerned with the principles of heat transfer and fluid dynamics as applied specifically to Advanced Light Water Reactor systems. It investigates the complex thermal-hydraulic phenomena occurring within the reactor core, coolant loops, and associated components under both steady-state and transient conditions, including single-phase and two-phase flow, boiling, condensation, and critical heat flux. Its significance lies in providing the fundamental understanding necessary for the safe, efficient, and reliable design, performance prediction, safety analysis, and regulatory licensing of ALWR technologies.