Research on the flywheel clearance flow in canned motor RCP

Abstract

Canned motor reactor coolant pump (canned motor RCP) is one of the most important parts of the reactor coolant system (RCS), the safety and stability of the canned motor RCP is the guarantee of the reactor security. Flywheels are introduced in the canned motor RCP to improve the coasting performance. When the canned motor RCP works, the reactor coolant water flows through the guard ring of the flywheel and the wall of stator, forming a clearance flow with large axial thermal gradient. The structure of the clearance flow directly affects the distribution of the temperature. So study on the flow and heat transfer characteristics of the clearance flow is necessary for the safety of the canned motor RCP. A varying clearance width transient CFD method is presented and used in the study of the clearance flow in this work. The results indicate that the friction loss induced by the clearance flow would decrease as the clearance width increases within certain limits, but the friction loss would increase with the increases of the clearance width if the clearance width exceed a certain range. As to the thermal barrier function of the clearance flow, the function would be weakened as the clearance width increases. These two effects should both be taken into consideration in the designing of flywheel clearance.