Mechanistic model for predicting two-phase behavior in CANDU reactor pumps

The behavior of the primary coolant pumps driven in two-phase flow plays an important role in determining the magnitude and direction of the core flow. This critically dominates the core heat transfer mechanisms. Loss-of-coolant accident (LOCA) conditions and a dryout in the reactor core may force steam to be carried through the pumps. Therefore, the flow through the pump under these conditions cannot be treated as a single-phase flow. Review of the existing thermohydraulic transient codes and pump models revealed that there are instability problems associated with the pump modeling. This is due to the methodology of modeling, the pump interaction with primary system fluid, and particularly to the two-phase flow degradation in the pump. Therefore, the need arises to develop an improved, reliably accurate model to describe the interaction between primary system fluid and the centrifugal pump during severe transients in CANDU reactors. It is strongly believed that the described model will enhance the capabilities of CANDU transient thermohydraulic codes in predicting the reactor's coolant pump behavior