Symposium on Advanced Sensors and Modeling Techniques for Nuclear Reactor Safety

Design of Natural Circulation Systems: Issues and Challenges

Natural circulation systems are characterized by their simplicity and higher reliability. It is because of this reason that many of the next generation nuclear power plants propose to use natural circulation as the heat removal mode either during normal operational states or during off-normal operational states. Indian Advanced Heavy Water Reactor (AHWR) and Prototype Fast Breeder Reactor (PFBR), Westinghouse’s AP-600, General Electric’s Economic Simplified Boiling Water Reactor (ESBWR), Russian VVER-1000 and Argentina’s CAREM, are just to name a few. While AHWR, ESBWR and CAREM use natural circulation for heat removal during all operational states, other reactors use natural circulation for decay heat removal. Despite their higher reliability and simplicity, these systems also have their own set of challenges. One of the key issues is that these systems are susceptible to different types of flow instabilities. These instabilities pose a challenge to system operation and control. A study of their mechanism and characteristics is must for the safe and reliable operation of these systems. In this presentation, the design of such systems will be discussed. The results of experimental investigations carried out in natural circulation system are presented. Several types of flow instabilities observed in experimental facilities are discussed. Thermal-hydraulic behaviour of these facilities has been predicted using both linear and non-linear stability analysis tools. The presentation describes some of these techniques. Results of comparison between model predictions and experimentally observed behaviour are also discussed.