Patent Number: 
Section: claims

1. A metal fuel pin system for a nuclear reactor, the system comprising:an annular metal nuclear fuel alloy, wherein a central hole provides for an effective fuel density of 75% or less upon irradiation;a zirconium sheath surrounding and fit tightly to the metal nuclear fuel alloy;a cladding surrounding the sheath; anda gas plenum. 2. The system of claim 1, wherein the metal nuclear fuel alloy comprises uranium-zirconium. 3. The system of claim 1, wherein the metal nuclear fuel alloy comprises uranium-molybdenum. 4. The system of claim 1, wherein the metal nuclear fuel alloy comprises transuranic elements. 5. The system of claim 1, wherein the metal nuclear fuel alloy comprises thorium alloys. 6. The system of claim 1, wherein the gas plenum is filled with helium. 7. The system of claim 1, wherein the cladding is steel. 8. The system of claim 1, wherein the metal nuclear fuel alloy acts like a traditional metal fuel upon irradiation. 9. The system of claim 1, wherein the metal nuclear fuel alloy is cast into the zirconium sheath to form a unitary product. 10. A metal fuel mold system comprising:a mold block with a cylindrical hole for receiving metal nuclear fuel alloy;a central rod within the cylindrical hole; anda zirconium sheath lining the cylindrical hole. 11. The system of claim 10, wherein the mold block comprises graphite. 12. The system of claim 10, wherein the central rod comprises steel coated with titanium nitride or a threaded solid graphite rod. 13. The system of claim 10, wherein the metal nuclear fuel alloy comprises uranium-zirconium. 14. The system of claim 10, wherein the metal nuclear fuel alloy comprises uranium-molybdenum. 15. The system of claim 10, wherein the metal nuclear fuel alloy further comprises transuranic elements. 16. The system of claim 10, wherein the metal nuclear fuel alloy comprises thorium alloys. 17. The system of claim 10, wherein the system is adapted for bottom pour casting. 18. A method of fabricating a sheathed, annular metal nuclear fuel, the method comprising:bottom pouring a liquid metal nuclear fuel alloy into a mold, wherein the mold comprises a set of holes within the mold, a rod in the approximate center of each of the holes, and a zirconium sheath within each of the one or more holes;allowing the liquid metal nuclear fuel alloy to form a sheathed, annular metal fuel;removing the sheathed, annular metal fuel; andplacing the sheathed, annular metal fuel in a cladding with a gas plenum. 19. The method of claim 18, wherein the one or more tubes are placed into a cladding prior to bottom pouring. 20. The method of claim 18, wherein the rod is a titanium nitride coated steel rod or a threaded solid graphite rod. 21. The method of claim 18, wherein the metal nuclear fuel alloy comprises uranium-zirconium. 22. The method of claim 18, wherein the metal nuclear fuel alloy comprises uranium-molybdenum. 23. The method of claim 18, wherein the metal nuclear fuel alloy comprises transuranic elements. 24. The method of claim 18, wherein the metal nuclear fuel alloy comprises thorium alloys. 25. The method of claim 18, further comprising remote fabrication of reprocessed fuel. 26. A method of using an annular metal fuel slug, the method comprising:providing an annular metal fuel slug created by bottom pour casting;initially irradiating of the annular metal fuel slug; andwherein the annular metal fuel slug acts like a traditional metal fuel after initial irradiation. 27. The method of claim 26, further comprising remote fabrication of reprocessed fuel. 28. The method of claim 26, further comprising removing minor actinides from spent fuel and alloying the minor actinides with new metal fuel. 29. The method of claim 26, further comprising providing a zirconium sheath surrounding the annular metal fuel slug. 30. The method of claim 26, wherein the annular metal fuel slug comprises thorium alloys.