Patent Number: 
Section: claims

1. A molten fuel nuclear reactor comprising:a containment vessel and vessel head enclosing a volume;a reactor core configured to contain molten fuel salt enclosed within the volume, the reactor core having an upper region and a lower region;a neutron reflector within the volume, the neutron reflector configured to contain at least some neutron-reflecting liquid;a heat exchanger enclosed within the volume adjacent to a portion of the neutron reflector;a molten fuel salt flow path that passes through the reactor core and the heat exchanger wherein the heat exchanger is configured to transfer heat from molten fuel salt passing through the heat exchanger to a primary coolant and further configured to transfer heat from the adjacent neutron reflector to the primary coolant;anda neutron-reflecting liquid flow path, separate from the molten fuel salt flow path, that passes the at least some neutron-reflecting liquid in the neutron reflector through the portion of the neutron reflector. 2. The molten fuel nuclear reactor of claim 1, wherein the at least some neutron-reflecting liquid is selected from lead, lead alloys, lead-bismuth eutectic, lead oxide, iron uranium alloys, iron-uranium eutectic, graphite, tungsten carbide, densalloy, titanium carbide, depleted uranium alloys, tantalum tungsten, and tungsten alloys. 3. The molten fuel nuclear reactor of claim 1, wherein the at least some neutron-reflecting liquid exhibits an elastic cross section of 0.1 barns or greater for 0.001 MeV neutrons. 4. The molten fuel nuclear reactor of claim 1, wherein the at least some neutron-reflecting liquid has a density greater than 10 grams/cm3 at the reactor operating temperature. 5. The molten fuel nuclear reactor of claim 1 wherein the heat exchanger enclosed within the volume is a first heat exchanger and the molten fuel nuclear reactor further comprises:a second heat exchanger through which the neutron-reflecting liquid passes, the second heat exchanger configured to remove heat from heated neutron-reflecting liquid and discharge cooled neutron-reflecting liquid. 6. The molten fuel nuclear reactor of claim 5, wherein the second heat exchanger is outside of the reactor vessel. 7. The molten fuel nuclear reactor of claim 6, further comprising:a liquid reflector coolant inlet in the vessel head fluidly connected to the second heat exchanger that receives cooled neutron-reflecting liquid;a liquid reflector coolant outlet in the vessel head fluidly connected to the second heat exchanger that discharges heated neutron-reflecting liquid; andan inlet reflector transport channel interior to and in contact with a first portion of the containment vessel between the liquid reflector coolant inlet and the liquid reflector coolant outlet, wherein the inlet reflector transport channel receives cooled neutron-reflecting liquid from the liquid reflector coolant inlet, thereby cooling the first portion of the containment vessel. 8. The molten fuel nuclear reactor of claim 7, wherein the first portion of the containment vessel includes at least some of a side wall of the containment vessel or a bottom wall of the containment vessel. 9. The molten fuel nuclear reactor of claim 1, wherein the fuel salt includes one or more of the following fissile salts: UF6,UF4,UF3,ThCl4,UBr3,UBr4,PuCl3, UCl4, UCl3, UCl3F, or UCl2F2 and one or more of the following non-fissile salts: NaCl, MgCl2, CaCl2, BaCl2, KCl, SrCl2, VCl3, CrCl3, TiCl4, ZrCl4, ThCl4, AcCl3, NpCl4, AmCl3, LaCl3, CeCl3, PrCl3 or NdCl3. 10. The molten fuel nuclear reactor of claim 1, wherein the neutron reflector comprises:one or more walls enclosing a chamber configured to contain at least some neutron-reflecting liquid, the chamber located between the reactor core and the heat exchanger. 11. The molten fuel nuclear reactor of claim 10, wherein the neutron-reflecting liquid flow path comprises moving the neutron-reflecting liquid in the chamber. 12. The molten fuel nuclear reactor of claim 10, wherein a first wall or first portion of a wall separates the chamber from the reactor core. 13. The molten fuel nuclear reactor of claim 10, wherein a second wall or second portion of a wall separates the chamber from the heat exchanger. 14. The molten fuel nuclear reactor of claim 10 further comprising:an impeller in the molten fuel salt flow path configured to drive flow of the molten fuel salt. 15. The molten fuel nuclear reactor of claim 10 further comprising:a pump in the neutron-reflecting liquid flow path configured to drive flow of the neutron-reflecting liquid. 16. The molten fuel nuclear reactor of claim 10, wherein molten fuel salt flow path passes around the chamber. 17. The molten fuel nuclear reactor of claim 16, wherein molten fuel salt flow path passes above and below the chamber. 18. The molten fuel nuclear reactor of claim 10, wherein the heat exchanger is a shell and tube heat exchanger comprising:a shell containing a plurality of tubes, at least a portion of the shell between the chamber and the plurality of tubes. 19. The molten fuel nuclear reactor of claim 18, wherein the molten fuel salt flow path passes through the plurality of tubes such that primary coolant in the shell removes heat directly from the tubes and the portion of the shell between the chamber and the plurality of tubes. 20. The molten fuel nuclear reactor of claim 18, wherein the molten fuel salt flow path passes through the shell such that primary coolant in the tubes removes heat directly from the molten fuel salt in the shell and, thereby, indirectly removes heat from neutron-reflecting liquid in the chamber via the portion of the shell between the chamber and the plurality of tubes.