Patent Number: 
Section: claims

1. A method of controlling a nuclear fission traveling wave reactor, the method comprising:for a nuclear fission traveling wave burnfront propagating along first and second dimensions in a nuclear fission reactor core, determining 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; anddetermining 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. 2. The method of claim 1, further comprising:determining an existing shape of the nuclear fission traveling wave burnfront. 3. The method of claim 1, wherein determining 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 responsive to the desired shape includes determining 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 method of claim 1, wherein determining 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 responsive to the desired shape includes determining 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 method of claim 1, further comprising:determining 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 method of claim 1, further comprising:migrating 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. 7. The method of claim 1, wherein the plurality of nuclear fission fuel subassemblies are elongate along the second dimension. 8. The method of claim 1, wherein the first dimension is substantially orthogonal to an elongated axis of the plurality of nuclear fission subassemblies. 9. The method of claim 1, wherein the first dimension and the second dimension are substantially orthogonal to each other. 10. The method of claim 1, wherein:the first dimension includes a radial dimension; andthe second dimension includes an axial dimension. 11. The method of claim 1, wherein:the first dimension includes an axial dimension; andthe second dimension includes a radial dimension. 12. The method of claim 1, wherein:the first dimension includes an axial dimension; andthe second dimension includes a lateral dimension. 13. The method of claim 1, wherein:the first dimension includes a lateral dimension; andthe second dimension includes an axial dimension. 14. The method of claim 1, wherein:the first locations are intermediate the second locations and an exterior of the nuclear fission reactor core. 15. The method of claim 14, 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. 16. The method of claim 14, 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. 17. The method of claim 14, 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. 18. The method of claim 1, wherein:the first locations include inward locations; andthe second locations include outward locations. 19. The method of claim 18, wherein the inward locations and outward locations are based on geometrical proximity to a central portion of the reactor core. 20. The method of claim 18, 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. 21. The method of claim 18, 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. 22. The method of claim 1, wherein the first locations and the second locations are located on opposite sides of a reference value along the first dimension. 23. The method of claim 1, wherein the first locations and the second locations include at least one attribute that is substantially equalized. 24. The method of claim 23, wherein the at least one attribute includes an attribute chosen from geometrical proximity to a central region of the reactor core, neutron flux, and reactivity. 25. The method of claim 1, wherein determining 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 includes determining a rotation of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 26. The method of claim 1, wherein determining 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 includes determining an inversion of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 27. The method of claim 1, wherein the selected set of dimensional constraints includes a predetermined maximum distance along the second dimension. 28. The method of claim 1, wherein the selected set of dimensional constraints is a function of at least one burnfront criteria. 29. The method of claim 28, wherein the burnfront criteria includes neutron flux. 30. The method of claim 29, wherein the neutron flux is associated with at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 31. The method of claim 28, wherein the burnfront criteria includes neutron fluence. 32. The method of claim 31, wherein the neutron fluence is associated with at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 33. The method of claim 28, wherein the burnfront criteria includes burnup. 34. The method of claim 33, wherein the burnup is associated with at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 35. The method of claim 28, wherein the burnfront criteria includes burnfront location within at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 36. The method of claim 1, wherein determining 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 includes determining 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. 37. The method of claim 1, wherein determining 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 includes determining 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. 38. The method of claim 1, wherein determining 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 includes determining an axial translation of selected ones of the plurality of nuclear fission fuel subassemblies. 39. The method of claim 1, wherein the desired shape of the nuclear fission traveling wave burnfront includes a shape chosen from a substantially spherical shape, 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. 40. The method of claim 1, wherein the desired shape of the nuclear fission traveling wave burnfront is asymmetrical. 41. The method of claim 40, wherein the desired shape of the nuclear fission traveling wave burnfront is rotationally asymmetrical around the second dimension.