Patent Number: 
Section: claims

1. A motor-driven centrifugal pump for circulating a coolant in a primary circuit of a nuclear reactor, the pump comprising:a sealed motor unit comprising a dry stator and an immersed rotor;a hydraulic part having an impeller; anda shaft which is immersed in the coolant, turned by the sealed motor unit and configured to pump the coolant via the impeller of the hydraulic part, the impeller and the immersed rotor being secured to the shaft, whereinthe motor-driven pump further comprises a thermal barrier between the motor unit and the hydraulic part, and through which the shaft passes, such that the motor unit is configured to be thermally isolated, the thermal barrier separating the motor-driven pump between a cold part comprising the motor unit and a hot part comprising the hydraulic part,the motor-driven pump also comprises an immersed flywheel mounted securely on the shaft between the rotor of the motor unit and the impeller of the hydraulic part to ensure a minimum amount of reactor cooling when the motor unit ceases to turn the shaft, andthe flywheel comprises a vaned wheel that includes at least one of fins, channels, and grooves formed on an upper surface of the flywheel facing toward the rotor, generating a circulation of the coolant around the flywheel from the cold part toward the hot part of the pump. 2. The motor-driven centrifugal pump as claimed in claim 1, further comprising an external cooling circuit connected to the motor unit, through which the coolant driven by the vaned wheel circulates, the cooled coolant being reintroduced into the motor unit. 3. The motor-driven centrifugal pump as claimed in claim 2, wherein the external cooling circuit comprises at least one coil wound on a body of the motor-driven pump the coolant circulating through the at least one coil being cooled via a secondary coolant circulating around the body in a shell. 4. The motor-driven centrifugal pump as claimed in claim 1, wherein the thermal barrier comprises a feed duct configured to allow a radial bearing to be lubricated by the coolant via the circulation of coolant generated by the vaned wheel. 5. The motor-driven centrifugal pump as claimed in claim 1, wherein the vaned wheel includes the channels or the grooves on the upper surface of the flywheel. 6. The motor-driven centrifugal pump as claimed in claim 1, further comprising at least three radial bearings that guide the rotation of the shaft, the at least three radial bearings including a first radial bearing, a second radial bearing, and a third radial bearing, whereinthe rotor is positioned between the first radial bearing and the second radial bearing,the flywheel is positioned between the second radial bearing and the third radial bearing, andthe circulation of coolant generated by the vaned wheel is configured to lubricate the third radial bearing. 7. The motor-driven centrifugal pump as claimed in claim 6, wherein the first radial bearing and the second radial bearing are hydrodynamic bearings of the plain bearing, pad bearing and/or three-lobe bearing type, and the third radial bearing is a hydrostatic bearing. 8. The motor-driven centrifugal pump as claimed in claim 6, comprising an axial bearing positioned near the first radial bearing and able to block axial movement of the shaft. 9. The motor-driven centrifugal pump as claimed in claim 8, wherein the axial bearing is a tilting-pad bearing. 10. The motor-driven centrifugal pump as claimed in claim 1, wherein the flywheel is made of a NiCr22Mo9Nb alloy. 11. The motor-driven centrifugal pump as claimed in claim 1, comprising an anti-backspin device able to mechanically prevent the rotation of the shaft in a predetermined direction.