Natural Circulation Flow Behavior at Reduced Inventory Conditions

Abstract

The flow instability behaviour of a natural circulation loop was studied at reduced inventory conditions, which is important during a LOCA situation in a nuclear reactor with non-availability of circulating pumps. For this, experiments were conducted at low steam drum levels. Large amplitude U-tube type oscillations were observed at low power condition when the system was mostly under single-phase condition. With rise in power when boiling was initiated in the loop, low quality Type I density-wave instabilities were observed. The characteristics of Type I instabilities are found to be quite different from the oscillations observed under single-phase conditions.