Patent Number: 
Section: claims

1. A method of operating a nuclear fission reactor, comprising:producing at least a portion of a traveling burn wave at a location relative to a nuclear fission module; andoperating a flow control assembly coupled to the nuclear fission module to modulate flow of a coolant in response to the location of the traveling burn wave relative to the nuclear fission module, the flow control assembly comprising a flow regulator subassembly having a first sleeve having a first hole and a second sleeve inserted into the first sleeve, the second sleeve having a second hole alignable with the first hole as the first sleeve translates in an axial direction relative to the second sleeve. 2. The method of claim 1, wherein operating the flow control assembly comprises modifying the flow regulator subassembly in response to an operating parameter associated with the nuclear fission module. 3. The method of claim 1, wherein operating the flow control assembly comprises reconfiguring the flow regulator subassembly according to a predetermined input to the flow regulator subassembly. 4. The method of claim 1, wherein operating the flow control assembly comprises achieving a controllable flow resistance via the flow regulator subassembly. 5. The method of claim 1, further comprising coupling a temperature sensor to the nuclear fission module and the flow regulator subassembly. 6. The method of claim 1, further comprising controlling flow of the coolant in response to the location relative to the nuclear fission module by operating the flow regulator subassembly according to when the burn wave arrives at the location relative to the nuclear fission module. 7. The method of claim 1, further comprising controlling flow of the coolant in response to the location relative to the nuclear fission module by operating the flow regulator subassembly according to when the burn wave departs from the location relative to the nuclear fission module. 8. The method of claim 1, further comprising controlling flow of the coolant in response to the location relative to the nuclear fission module by operating the flow regulator subassembly according to when the burn wave is proximate to the location relative to the nuclear fission module. 9. The method of claim 1, further comprising controlling flow of the coolant according to a width of the burn wave. 10. The method of claim 1, further comprising controlling flow of the coolant by operating the flow control assembly according to a heat generation rate in the nuclear fission module. 11. The method of claim 1, further comprising controlling flow of the coolant by operating the flow control assembly according to a temperature in the nuclear fission module. 12. The method of claim 1, further comprising controlling flow of the coolant by operating the flow control assembly according to a neutron flux in the nuclear fission module. 13. The method of claim 1, wherein:the nuclear fission module has a temperature dependent reactivity change; andthe flow control assembly controls the temperature dependent reactivity change within the nuclear fission module. 14. The method of claim 1, wherein producing at least a portion of a traveling burn wave comprises producing at least a portion of the traveling burn wave at a location relative to a nuclear fission fuel assembly. 15. The method of claim 1, wherein producing at least a portion of a traveling burn wave comprises producing at least a portion of the traveling burn wave at a location relative to a fertile nuclear breeding assembly. 16. The method of claim 1, wherein producing at least a portion of a traveling burn wave comprises producing at least a portion of the traveling burn wave at a location relative to a neutron reflector assembly. 17. A method of operating a nuclear fission reactor, comprising:producing at least a portion of a traveling burn wave at a location relative to a nuclear fission module; andcontrolling flow of a coolant in response to the location of the traveling burn wave relative to the nuclear fission module with a flow control assembly by relatively axially translating a first sleeve having a first hole and a second sleeve inserted into the first sleeve, the second sleeve having a second hole alignable with the first hole. 18. The method of claim 17, wherein relatively axially translating the first sleeve having the first hole and the second sleeve having the second hole comprises rotating a member coupled to the first sleeve. 19. The method of claim 17, wherein controlling the flow of coolant comprises controlling the flow of coolant in response to an operating parameter associated with the nuclear fission module.