Analysis of hydraulic lift force of a fuel assembly

The exact expression for the lift force on a fuel assembly in a reactor core is derived in terms of calculable hydraulic parameters. The relation for the lift force, pressure drop, buoyancy force, viscous force, and fuel assembly weight is discussed. Based on the derived exact expression, error analysis is made for a simple expression applying COBRA IV-i to a typical PWR assembly. The error analysis revealed that the error of the simple expression consists of four terms and the overall error depends on the flow rate change direction and its magnitude is about 1%