EM Pump and Orificing

Four ElectroMagnetic (EM) pumps are positioned in the reactor vessel. Each pump pulls cooled Sodium descending from the top of the vessel into the downcomer to be pumped into the bottom of the core. The pump is totally submerged in the Sodium in the vessel which eliminates the need for large pipes leaving the vessel at core level filled with liquid Sodium. This in turn eliminates the the possibility of the core becoming uncovered through a loss of coolant accident.

Each assembly in the core is orificed differently. The term orificing is used to describe the ability of controlling coolant flow rates in assemblies by controlling the flow area of the inlet orifices of the assemblies. If the inlet area is small, then the flow rate will be less than if the inlet area is large. Thus, each assembly can have the ideal flow rate necessary to keep the sodium outlet temperatures uniform even though the thermal powers of the assemblies may be different. It is desirable for the outlet temperature to be radially uniform because otherwise thermal stresses will be felt by components above the core. This is called thermal striping.