Natural Circulation Cooling in a Pressurized Water Reactor Geometry Under Accident-Induced Conditions

The characteristics and limits of natural circulation heat rejection over a wide range of conditions were experimentally investigated in a small-scale model of a pressurized water reactor. Conditions that were varied included primary and secondary coolant inventory, decay heat power, and primary noncondensible gas content. The results have defined three distinct modes of natural circulation, their limits and transition points, and the characteristic “signatures” accompanying natural circulation behavior. Particular emphasis is focused on the limits of natural circulation under severely degraded primary and secondary conditions.