Patent Number: 046831118
Section: claims

1. A gas circulator for a nuclear reactor, comprising: a stator;  a rotor having a rotor shaft with a first end and a second end;  an impeller attached to the first end of the rotor shaft;  a first radial active magnetic bearing positioned proximate the first end of the rotor shaft;  a first radial backup bearing positioned proximate the first end of the rotor shaft;  a second radial active magnetic bearing positioned proximate the second end of the rotor shaft;  a second radial backup bearing positioned proximate the second end of the rotor shaft;  an axial active magnetic bearing positioned between the first and second ends of the rotor shaft; and  an axial backup bearing positioned between the first and second ends of the rotor shaft;  wherein two of the backup bearings are located within a sealed chamber.  supporting the circulator radially with a first active magnetic bearing and a second active magnetic bearing;  supporting the circulator axially with a third active magnetic bearing;  providing a first backup bearing for the first active magnetic bearing;  providing a second backup bearing for the second active magnetic bearing;  providing a third backup bearing for the third active magnetic bearing; and  locating the second and third backup bearings in a sealed chamber.  a nuclear reactor contained within a primary system pressure boundary;  a gas coolant for the nuclear reactor; and  a gas circulator including a stator, a rotor having a rotor shaft with a first end and a second end, an impeller attached to the rotor shaft at the first end of the rotor shaft, a first radial active magnetic bearing positioned proximate the first end of the rotor shaft, a first radial backup bearing positioned proximate the first end of the rotor shaft, a second radial active magnetic bearing positioned proximate the second end of the rotor shaft, a second radial backup bearing positioned proximate the second end of the rotor shaft, an axial active magnetic bearing positioned between the first and second ends of the rotor shaft, an axial backup bearing positioned between the first and second ends of the rotor shaft;  wherein the gas circulator is contained within the primary system pressure boundary.  pumping a coolant through the nuclear reactor with a pump;  supporting the pump radially with two active magnetic bearings;  supporting the pump axially with an active magnetic bearing;  providing backup bearings for the radial active magnetic bearings;  providing a backup bearing for the axial active magnetic bearing; and  enclosing one radial backup bearing and the axial backup bearing in a sealed chamber. 2. A gas circulator as defined in claim 1, wherein the chamber contains a lubricant. 3. A gas circulator as defined in claim 2, wherein the lubricant is a solid lubricant. 4. A gas circulator as defined in claim 2, wherein the lubricant is a liquid lubricant. 5. A gas circulator as defined in claim 1, wherein the second radial backup bearing and the axial backup bearing are located within the chamber. 6. A gas circulator as defined in claim 5, wherein the second radial backup bearing is an antifriction bearing and wherein the axial backup bearing is an antifriction bearing. 7. A gas circulator as defined in claim 5, wherein the first radial backup bearing includes a graphite bushing mounted on the stator. 8. A gas circulator as defined in claim 7, wherein the first radial backup bearing further includes a metal sleeve mounted on the rotor shaft. 9. A gas circulator as defined in claim 5, wherein the axial backup bearing and second radial backup bearing are spaced apart sufficiently to permit the backup bearings to provide substantially all radial support for the rotor when the first and second radial active magnetic bearings are deenergized. 10. A gas circulator as defined in claim 5, wherein the sealed chamber is defined by an inner member, an outer member, and sealing means for forming a seal between the inner and outer members, the outer member being substantially annular and at least part of the inner member being located within the outer member. 11. A gas circulator as defined in claim 10, wherein one of the rotor shaft and the inner member has a bore and the other of the rotor shaft and the inner member has an extension with a first end and a second end, the extension extending into the bore, a clearance existing between the extension and the bore when the active magnetic bearings are energized. 12. A gas circulator as defined in claim 11, wherein the rotor shaft has the bore and the inner member has the extension, the first end of the extension extending into the bore, the second end of the extension being connected to the inner member. 13. A gas circulator as defined in claim 12, wherein the second end of the extension is beveled and the rotor shaft is correspondingly beveled. 14. A gas circulator as defined in claim 12, wherein the first end of the extension is beveled and the rotor shaft is correspondingly beveled. 15. A gas circulator as defined in claim 11, wherein the inner member has the bore and the rotor shaft has the extension, the first end of the extension extending into the bore, the second end of the extension being connected to the second end of the rotor shaft. 16. A gas circulator as defined in claim 15, wherein the second end of the extension is beveled and the inner member is correspondingly beveled. 17. A gas circulator as defined in claim 10, further comprising means for braking the rotor. 18. A gas circulator as defined in claim 17, wherein the means for braking the rotor includes a first flange connected to the rotor shaft, a second flange connected to the inner member, and means for loading the first flange and the second flange at their respective beveled contacting surfaces. 19. A gas circulator as defined in claim 10, wherein the chamber contains a liquid lubricant, and wherein means for preventing the liquid lubricant from traveling toward the rotor shaft are located within the chamber. 20. A gas circulator as defined in claim 19, wherein the preventing means includes a ring which by centrifugal force urges the liquid lubricant away from the rotor shaft. 21. A gas circulator as defined in claim 5, further comprising control means for adjusting the position of the rotor while the rotor is rotating. 22. A gas circulator as defined in claim 21, wherein the control means includes means for sensing rotor vibrations and means for reducing rotor vibrations. 23. A method for using a circulator for a gas-cooled nuclear reactor, comprising the steps of: 24. A method as defined in claim 23, further comprising the step of electrically driving the circulator. 25. A method as defined in claim 23, wherein the supporting steps and the providing steps are performed within a primary system pressure boundary for the nuclear 26. A method as defined in claim 23, further comprising the step of introducing a lubricant into the 27. A method as defined in claim 26, wherein the introducing step includes introducing a solid lubricant into the chamber. 28. A method as defined in claim 26, wherein the introducing step includes introducing a liquid lubricant into the chamber. 29. A method as defined in claim 23, further comprising the step of supplying a braking mechanism for the circulator. 30. A method as defined in claim 23, further comprising the step of installing the circulator with a rotor shaft in a substantially horizontal orientation. 31. A method as defined in claim 23, further comprising the step of installing the circulator with a rotor shaft in a substantially vertical orientation. 32. A method as defined in claim 31, wherein the locating step includes locating both of the second and third backup bearings in a sealed chamber positioned proximate the bottom of the rotor shaft. 33. A method as defined in claim 32, wherein each providing step includes providing an antifriction backup bearing. 34. A nuclear reactor system, comprising: 35. A nuclear reactor system as defined in claim 34, wherein the rotor shaft has a substantially vertical orientation. 36. A nuclear reactor system as defined in claim 35, wherein the second radial backup bearing and the axial backup bearing are located within a sealed chamber. 37. A nuclear reactor system as defined in claim 36, wherein the first radial backup bearing includes a graphite bushing mounted on the stator, wherein the second radial backup bearing is an antifriction bearing, and wherein the axial backup bearing is an antifriction bearing. 38. A nuclear reactor system as defined in claim 37, wherein the first radial backup bearing further includes a metal sleeve mounted on the rotor shaft. 39. A nuclear reactor system as defined in claim 34, further comprising control means for controlling the active magnetic bearings to adjust the position of the rotor. 40. A nuclear reactor system as defined in claim 39, wherein the control means includes means for suppressing rotor vibrations. 41. A nuclear reactor system as defined in claim 34, wherein the active magnetic bearings include windings and wherein the windings are sealed off from the gas coolant. 42. A method for operating a nuclear reactor, comprising the steps of: 43. A method as defined in claim 42, wherein the pumping step includes pumping a gas coolant through the nuclear reactor. 44. A method as defined in claim 42, wherein the pumping step includes pumping the coolant with an electrically driven pump. 45. A method as defined in claim 42, wherein the pumping step includes pumping the coolant with a pump having a substantially vertical shaft. 46. A method as defined in claim 42, wherein the pumping step includes pumping the coolant with a pump having a substantially horizontal shaft. 47. A method as defined in claim 42, further comprising the step of introducing a lubricant into the chamber. 48. A method as defined in claim 47, wherein the introducing step includes introducing a solid lubricant into the chamber. 49. A method as defined in claim 47, wherein the introducing step includes introducing a liquid lubricant into the chamber. 50. A method as defined in claim 42, wherein the providing and enclosing steps are performed within a primary system pressure boundary for the nuclear reactor. 51. A method as defined in claim 42, wherein each active magnetic bearing includes a stator, further comprising the step of sealing off the stators of the active magnetic bearings from the coolant.