Patent Number: 
Section: claims

1. A nuclear fission reactor comprising:a reactor vessel;a nuclear fission reactor core disposed in the reactor vessel, the nuclear fission reactor core including:a central core region including:a plurality of fissile nuclear fuel assemblies;ones of a plurality of fertile nuclear fuel assemblies; anda plurality of movable reactivity control assemblies; anda peripheral core region located radially outward from the central core region and radially inward of a radial shield of the core, the peripheral core region including:others of the plurality of fertile nuclear fuel assemblies; anda plurality of neutron absorber assemblies disposed among the others of the plurality of fertile nuclear fuel assemblies in the peripheral core region, locations of the plurality of neutron absorber assemblies selected from predetermined radial locations in the peripheral core region based upon a predetermined stage of core life of the others of the plurality of fertile nuclear fuel assemblies and any other nuclear fuel assemblies of the peripheral core region;an in-vessel handling system configured to shuffle ones of the plurality of fissile nuclear fuel assemblies and ones of the plurality of fertile nuclear fuel assemblies; anda reactor coolant system. 2. The nuclear fission reactor of claim 1, wherein the in-vessel handling system is further configured to shuffle ones of the plurality of fissile nuclear fuel assemblies and ones of the plurality of fertile nuclear fuel assemblies between the central core region and the peripheral core region. 3. The nuclear fission reactor of claim 1, wherein the plurality of fissile nuclear fuel assemblies includes:a plurality of enriched fissile nuclear fuel assemblies; anda plurality of bred fissile nuclear fuel assemblies. 4. The nuclear fission reactor of claim 3, wherein the peripheral core region further includes ones of the plurality of bred fissile nuclear fuel assemblies. 5. The nuclear fission reactor of claim 3, wherein the peripheral core region further includes selected ones of the plurality of enriched fissile nuclear fuel assemblies having at least a predetermined burnup level. 6. The nuclear fission reactor of claim 3, wherein the peripheral core region further includes selected ones of the plurality of bred fissile nuclear fuel assemblies having at least a predetermined burnup level. 7. The nuclear fission reactor of claim 3, wherein the peripheral core region further includes ones of the plurality of bred fissile nuclear fuel assemblies having less than a predetermined burnup level. 8. The nuclear fission reactor of claim 1, wherein:the plurality of fissile nuclear fuel assemblies includes a plurality of bred fissile nuclear fuel assemblies; andthe core peripheral region includes a plurality of enriched fissile nuclear fuel assemblies having at least a predetermined burnup level. 9. The nuclear fission reactor of claim 8, wherein the peripheral core region further includes ones of the plurality of bred fissile nuclear fuel assemblies. 10. The nuclear fission reactor of claim 9, wherein the peripheral core region further includes selected ones of the plurality of bred fissile nuclear fuel assemblies having at least a predetermined burnup level. 11. The nuclear fission reactor of claim 9, wherein the peripheral core region further includes ones of the plurality of bred fissile nuclear fuel assemblies having less than a predetermined burnup level. 12. The nuclear fission reactor of claim 1, wherein at least one of the plurality of fissile nuclear fuel assemblies includes fissile material discharged from a nuclear fission reactor. 13. The nuclear fission reactor of claim 12, wherein the plurality of fissile nuclear fuel assemblies that includes fissile material discharged from a nuclear fission reactor includes at least one re-clad fissile fuel assembly. 14. The nuclear fission reactor of claim 1, further comprising a plurality of fuel assembly flow receptacles defining:a first plurality of reactor coolant flow orifices in the central core region; anda second plurality of reactor coolant flow orifices in the peripheral core region. 15. The nuclear fission reactor of claim 14, wherein the first plurality of reactor coolant flow orifices includes a plurality of reactor coolant flow orifice groups. 16. The nuclear fission reactor of claim 15, wherein flow rate through a selected one of the plurality of reactor coolant flow orifice groups is based upon a power profile at a radial location of the selected one of the plurality of reactor coolant flow orifice groups. 17. The nuclear fission reactor of claim 14, wherein flow rate through the second plurality of reactor coolant flow orifices includes a predetermined flow rate based upon power level in the peripheral core region. 18. The nuclear fission reactor of claim 14, wherein the first and second pluralities of reactor coolant flow orifices include fixed orifices. 19. The nuclear fission reactor of claim 14, wherein the first and second pluralities of reactor coolant flow orifices include variable orifices. 20. The nuclear fission reactor of claim 14, wherein the first and second pluralities of reactor coolant flow orifices include fixed orifices and variable orifices. 21. The nuclear fission reactor of claim 1, wherein the in-vessel handling system is further configured to move ones of the plurality of neutron absorber assemblies among a plurality of locations in the peripheral core region. 22. The nuclear fission reactor of claim 21, wherein the plurality of locations in the peripheral core region include a plurality of predetermined radial locations in the peripheral core region that are selectable based upon a predetermined burnup level of nuclear fuel assemblies located in the peripheral core region. 23. The nuclear fission reactor of claim 1, wherein the in-vessel handling system is further configured to rotate ones of the plurality of neutron absorber assemblies. 24. The nuclear fission reactor of claim 1, wherein the in-vessel handling system is further configured to shuffle ones of the plurality of fissile nuclear fuel assemblies and ones of the plurality of fertile nuclear fuel assemblies between the central core region and a portion of the reactor vessel exterior the nuclear fission reactor core. 25. The nuclear fission reactor of claim 1, wherein the reactor coolant system includes a pool of liquid sodium disposed in the reactor vessel, the nuclear fission reactor core being submerged in the pool of liquid sodium. 26. The nuclear fission reactor of claim 1, wherein the neutron absorber assemblies are surrounded by the fertile fuel assemblies of the peripheral core region and inside the radial shield. 27. The nuclear fission reactor of claim 1, wherein at least a portion of the neutron absorber assemblies within the peripheral core region are not movable. 28. The nuclear fission reactor of claim 1, wherein at a beginning of life BoL of the nuclear fission reactor core, the peripheral core region includes no fissile nuclear fuel assemblies. 29. A nuclear fission reactor comprising:a reactor vessel;a nuclear fission reactor core disposed in the reactor vessel, the nuclear fission reactor core including:a central core region including:a plurality of fissile nuclear fuel assemblies;ones of a plurality of fertile nuclear fuel assemblies; anda plurality of movable reactivity control assemblies; anda peripheral core region located radially outward from the central core region and radially inward of a radial shield of the core, the peripheral core region including:others of the plurality of fertile nuclear fuel assemblies; anda plurality of neutron absorber assemblies disposed among the others of the plurality of fertile nuclear fuel assemblies in the peripheral core region, locations of the plurality of neutron absorber assemblies selected from predetermined radial locations in the peripheral core region based upon a predetermined stage of core life of the others of the plurality of fertile nuclear fuel assemblies and any other nuclear fuel assemblies of the peripheral core region;an in-vessel handling system configured to shuffle ones of the plurality of fissile nuclear fuel assemblies and ones of the plurality of fertile nuclear fuel assemblies;a reactor coolant system;a plurality of fuel assembly flow receptacles defining:a first plurality of reactor coolant flow orifices in the central core region; anda second plurality of reactor coolant flow orifices in the peripheral core region; anda decay heat removal system. 30. The nuclear fission reactor of claim 29, wherein the in-vessel handling system is further configured to shuffle ones of the plurality of fissile nuclear fuel assemblies and ones of the plurality of fertile nuclear fuel assemblies between the central core region and the peripheral core region. 31. The nuclear fission reactor of claim 29, wherein the plurality of fissile nuclear fuel assemblies includes:a plurality of enriched fissile nuclear fuel assemblies; anda plurality of bred fissile nuclear fuel assemblies. 32. The nuclear fission reactor of claim 31, wherein the peripheral core region further includes ones of the plurality of bred fissile nuclear fuel assemblies. 33. The nuclear fission reactor of claim 31, wherein the peripheral core region further includes selected ones of the plurality of enriched fissile nuclear fuel assemblies having at least a predetermined burnup level. 34. The nuclear fission reactor of claim 31, wherein the peripheral core region further includes selected ones of the plurality of bred fissile nuclear fuel assemblies having at least a predetermined burnup level. 35. The nuclear fission reactor of claim 31, wherein the peripheral core region further includes ones of the plurality of bred fissile nuclear fuel assemblies having less than a predetermined burnup level. 36. The nuclear fission reactor of claim 29, wherein:the plurality of fissile nuclear fuel assemblies includes a plurality of bred fissile nuclear fuel assemblies; andthe core peripheral region includes a plurality of enriched fissile nuclear fuel assemblies having at least a predetermined burnup level. 37. The nuclear fission reactor of claim 36, wherein the peripheral core region further includes ones of the plurality of bred fissile nuclear fuel assemblies. 38. The nuclear fission reactor of claim 37, wherein the peripheral core region further includes selected ones of the plurality of bred fissile nuclear fuel assemblies having at least a predetermined burnup level. 39. The nuclear fission reactor of claim 37, wherein the peripheral core region further includes ones of the plurality of bred fissile nuclear fuel assemblies having less than a predetermined burnup level. 40. The nuclear fission reactor of claim 29, wherein at least one of the plurality of fissile nuclear fuel assemblies includes fissile material discharged from a nuclear fission reactor. 41. The nuclear fission reactor of claim 40, wherein the plurality of fissile nuclear fuel assemblies that includes fissile material discharged from a nuclear fission reactor includes at least one re-clad fissile fuel assembly. 42. The nuclear fission reactor of claim 29, wherein the first plurality of reactor coolant flow orifices includes a plurality of reactor coolant flow orifice groups. 43. The nuclear fission reactor of claim 42, wherein flow rate through a selected one of the plurality of reactor coolant flow orifice groups is based upon a power profile at a radial location of the selected one of the plurality of reactor coolant flow orifice groups. 44. The nuclear fission reactor of claim 29, wherein flow rate through the second plurality of reactor coolant flow orifices includes a predetermined flow rate based upon power level in the peripheral core region. 45. The nuclear fission reactor of claim 29, wherein the first and second pluralities of reactor coolant flow orifices include fixed orifices. 46. The nuclear fission reactor of claim 29, wherein the first and second pluralities of reactor coolant flow orifices include variable orifices. 47. The nuclear fission reactor of claim 29, wherein the first and second pluralities of reactor coolant flow orifices include fixed orifices and variable orifices. 48. The nuclear fission reactor of claim 29, wherein the in-vessel handling system is further configured to move ones of the plurality of neutron absorber assemblies among a plurality of locations in the peripheral core region. 49. The nuclear fission reactor of claim 48, wherein the plurality of locations in the peripheral core region include a plurality of predetermined radial locations in the peripheral core region that are selectable based upon a predetermined burnup level of nuclear fuel assemblies located in the peripheral core region. 50. The nuclear fission reactor of claim 29, wherein the in-vessel handling system is further configured to rotate ones of the plurality of neutron absorber assemblies. 51. The nuclear fission reactor of claim 29, wherein the in-vessel handling system is further configured to shuffle ones of the plurality of fissile nuclear fuel assemblies and ones of the plurality of fissile nuclear fuel assemblies between the central core region and a portion of the reactor vessel exterior the nuclear fission reactor core. 52. The nuclear fission reactor of claim 29, wherein the reactor coolant system includes a pool of liquid sodium disposed in the reactor vessel, the nuclear fission reactor core being submerged in the pool of liquid sodium.