A review of modern advances in analyses and applications of single-phase natural circulation loop in nuclear thermal hydraulics

• Comprehensive review of state-of-the-art on single-phase natural circulation loops.
• Detailed discussion on growth in solar thermal system and nuclear thermal hydraulics.
• Systematic development in scaling methodologies for fabrication of test facilities.
• Importance of numerical modeling schemes for stability assessment using 1-D codes.
• Appraisal of current trend of research and possible future directions.

A comprehensive review of single-phase natural circulation loop (NCL) is presented here. Relevant literature reported since the later part of 1980s has been meticulously surveyed, with occasional obligatory reference to a few pioneering studies originating prior to that period, summarizing the key observations and the present trend of research. Development in the concept of buoyancy-induced flow is discussed, with introduction to flow initiation in an NCL due to instability. Detailed discussion on modern advancement in important application areas like solar thermal systems and nuclear thermal hydraulics are presented, with separate analysis for various reactor designs working on natural circulation. Identification of scaling criteria for designing lab-scale experimental facilities has gone through a series of modification. A systematic analysis of the same is presented, considering the state-of-the-art knowledge base. Different approaches have been followed for modeling single-phase NCLs, including simplified Lorenz system mostly for toroidal loops, 1-D computational modeling for both steady-state and stability characterization and 3-D commercial system codes to have a better flow visualization. Methodical review of the relevant studies is presented following a systematic approach, to assess the gradual progression in understanding of the practical system. Brief appraisal of current research interest is reported, including the use of nanofluids for fluid property augmentation, marine reactors subjected to rolling waves and exploring options to control system dynamics. Finally an effort is made to identify the possible direction of future research.