Patent Number: 
Section: claims

1. A system comprising:for a nuclear fission traveling wave burnfront propagating along first and second dimensions in a nuclear fission reactor core, first electrical circuitry configured to determine a desired shape of the nuclear fission traveling wave burnfront along the second dimension within a plurality of nuclear fission fuel subassemblies according to a selected set of dimensional constraints;second electrical circuitry configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations in the nuclear fission reactor core toward respective second locations in the nuclear fission reactor core in a manner responsive to the desired shape; anda subassembly configured to migrate selected ones of the plurality of nuclear fission fuel subassemblies responsive to the second electrical circuitry. 2. The system of claim 1, wherein the second electrical circuitry is further configured to determine an existing shape of the nuclear fission traveling wave burnfront. 3. The system of claim 1, wherein the second electrical circuitry is further configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner to establish the desired shape. 4. The system of claim 1, wherein the second electrical circuitry is further configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner to maintain the desired shape. 5. The system of claim 1, wherein the second electrical circuitry is further configured to determine a time when to migrate the selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. 6. The system of claim 1, wherein:the first dimension includes an axial dimension; andthe second dimension includes a radial dimension. 7. The system of claim 1, wherein:the first dimension includes an axial dimension; andthe second dimension includes a lateral dimension. 8. The system of claim 1, wherein:the first dimension includes a lateral dimension; andthe second dimension includes an axial dimension. 9. The system of claim 1, wherein:the first locations are intermediate the second locations and an exterior of the nuclear fission reactor core. 10. The system of claim 9, wherein an attribute of position within the nuclear fission reactor core of the second locations and the first locations include geometrical proximity to a central portion of the nuclear fission reactor core. 11. The system of claim 9, wherein the inward locations and the outward locations are based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. 12. The system of claim 9, wherein the inward locations and the outward locations are based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. 13. The system of claim 1, wherein:the first locations include inward locations; andthe second locations include outward locations. 14. The system of claim 13, wherein the inward locations and outward locations are based on geometrical proximity to a central portion of the reactor core. 15. The system of claim 13, wherein the inward locations and the outward locations are based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. 16. The system of claim 13, wherein the inward locations and the outward locations are based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. 17. The system of claim 1, wherein the second electrical circuitry is further configured to determine rotation of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 18. The system of claim 1, wherein the second electrical circuitry is further configured to determine inversion of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 19. The system of claim 1, wherein the subassembly includes a nuclear fuel handling apparatus. 20. The system of claim 1, wherein the subassembly is further configured to radially migrate selected ones of the plurality of nuclear fission fuel subassemblies from respective first locations toward respective second locations. 21. The system of claim 1, wherein the subassembly is further configured to spirally migrate selected ones of the plurality of nuclear fission fuel subassemblies from respective first locations toward respective second locations. 22. The system of claim 1, wherein the subassembly is further configured to axially translate selected ones of the plurality of nuclear fission fuel subassemblies. 23. The system of claim 1, wherein the subassembly is further configured to rotate selected ones of the plurality of nuclear fission fuel subassemblies. 24. The system of claim 1, wherein the subassembly is further configured to invert selected ones of the plurality of nuclear fission fuel subassemblies. 25. A nuclear fission traveling wave reactor comprising:a nuclear fission traveling wave reactor core;a plurality of nuclear fission fuel subassemblies received in the nuclear fission traveling wave reactor core, each of the plurality of nuclear fission fuel subassemblies being configured to propagate a nuclear fission traveling wave burnfront therein along first and second dimensions in the nuclear fission reactor core;first electrical circuitry configured to determine a desired shape of the nuclear fission traveling wave burnfront along the second dimension within a plurality of nuclear fission fuel subassemblies according to a selected set of dimensional constraints;second electrical circuitry configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations in the nuclear fission reactor core toward respective second locations in the nuclear fission reactor core in a manner responsive to the desired shape; anda subassembly configured to migrate selected ones of the plurality of nuclear fission fuel subassemblies responsive to the second electrical circuitry. 26. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine an existing shape of the nuclear fission traveling wave burnfront. 27. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner to establish the desired shape. 28. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner to maintain the desired shape. 29. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a time when to migrate the selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. 30. The reactor of claim 25, wherein the plurality of nuclear fission fuel subassemblies are elongate along the second dimension. 31. The reactor of claim 25, wherein the first dimension is substantially orthogonal to an elongated axis of the plurality of nuclear fission subassemblies. 32. The reactor of claim 25, wherein the first dimension and the second dimension are substantially orthogonal to each other. 33. The reactor of claim 25, wherein:the first dimension includes a radial dimension; andthe second dimension includes an axial dimension. 34. The reactor of claim 25, wherein:the first dimension includes an axial dimension; andthe second dimension includes a radial dimension. 35. The reactor of claim 25, wherein:the first dimension includes an axial dimension; andthe second dimension includes a lateral dimension. 36. The reactor of claim 25, wherein:the first dimension includes a lateral dimension; andthe second dimension includes an axial dimension. 37. The reactor of claim 25, wherein:the first locations are intermediate the second locations and an exterior of the nuclear fission reactor core. 38. The reactor of claim 37, wherein an attribute of position within the nuclear fission reactor core of the second locations and the first locations include geometrical proximity to a central portion of the nuclear fission reactor core. 39. The reactor of claim 37, wherein the inward locations and the outward locations are based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. 40. The reactor of claim 37, wherein the inward locations and the outward locations are based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. 41. The reactor of claim 25, wherein:the first locations include inward locations; andthe second locations include outward locations. 42. The reactor of claim 41, wherein the inward locations and outward locations are based on geometrical proximity to a central portion of the reactor core. 43. The reactor of claim 41, wherein the inward locations and the outward locations are based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. 44. The reactor of claim 41, wherein the inward locations and the outward locations are based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. 45. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine rotation of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 46. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine inversion of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 47. The reactor of claim 25, wherein the selected set of dimensional constraints includes a predetermined maximum distance along the second dimension. 48. The reactor of claim 25, wherein the selected set of dimensional constraints is a function of at least one burnfront criteria. 49. The reactor of claim 48, wherein the burnfront criteria includes neutron flux. 50. The reactor of claim 48, wherein the burnfront criteria includes neutron fluence. 51. The reactor of claim 48, wherein the burnfront criteria includes burnfront location within at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 52. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a radial migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. 53. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a spiral migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. 54. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine an axial translation of selected ones of the plurality of nuclear fission fuel subassemblies. 55. The reactor of claim 25, wherein the desired shape includes a shape chosen from a substantially spherical shape of the nuclear fission traveling wave burnfront, a shape conforming to a selected continuously curved surface, a shape that is substantially rotationally symmetrical around the second dimension, and a shape having substantial n-fold rotational symmetry around the second dimension. 56. The reactor of claim 25, wherein the desired shape of the nuclear fission traveling wave burnfront is asymmetrical. 57. The reactor of claim 25, wherein the subassembly includes a nuclear fuel handling apparatus. 58. The reactor of claim 25, wherein the subassembly is further configured to radially migrate selected ones of the plurality of nuclear fission fuel subassemblies from respective first locations toward respective second locations. 59. The reactor of claim 25, wherein the subassembly is further configured to spirally migrate selected ones of the plurality of nuclear fission fuel subassemblies from respective first locations toward respective second locations. 60. The reactor of claim 25, wherein the subassembly is further configured to axially translate selected ones of the plurality of nuclear fission fuel subassemblies. 61. The reactor of claim 25, wherein the subassembly is further configured to rotate selected ones of the plurality of nuclear fission fuel subassemblies. 62. The reactor of claim 25, wherein the subassembly is further configured to invert selected ones of the plurality of nuclear fission fuel subassemblies.