Patent Number: 
Section: claims

1. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being placed in the at least one retention bore such that at least a portion of the at least one irradiation target is embedded inside of the tie plate attachment,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the outer structure of the tie plate attachment is further shaped with an outer perimeter that corresponds to an outer perimeter of the tie plate. 2. The structure of claim 1, wherein the at least one hole is configured to permit an end plug of a fuel rod of the nuclear fuel assembly to pass through the tie plate attachment and into the tie plate. 3. The structure of claim 2, wherein the tie plate attachment is maintainable in an axial position by a shoulder at the joining of the fuel rod and the end plug. 4. The structure of claim 1, wherein the tie plate attachment is rectangular. 5. The structure of claim 1, wherein the tie plate attachment further includes at least one cap joined to the tie plate attachment over the at least one retention bore, the cap shaped to seal and fully enclose the irradiation target within the retention bore. 6. The structure of claim 5, wherein the irradiation target substantially converts to a liquid or gaseous radioisotope when exposed to the neutron flux in the operating nuclear reactor. 7. The structure of claim 5, wherein the irradiation target is at least one of a liquid and gas. 8. The structure of claim 1, wherein the irradiation target is at least one of Iridium-191, Selenium-74, Strontium-88, and Cobalt-59. 9. The structure of claim 1, wherein a plurality of irradiation targets are placed in the retention bore, at least a first irradiation target of the plurality being a first material and at least one of a second irradiation target of the plurality being a second material. 10. The structure of claim 1, wherein the at least one retention bore does not pass entirely through the tie plate attachment such that a bottom and sides of the bore are continuously defined by the tie plate attachment. 11. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore not passing entirely through the tie plate attachment such that a bottom and sides of the bore are continuously defined by the tie plate attachment, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being inside of and retained by the at least one retention bore,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the outer structure of the tie plate attachment is further shaped with an outer perimeter that corresponds to an outer perimeter of the tie plate. 12. The structure of claim 11, wherein the tie plate attachment is rectangular. 13. The structure of claim 11, wherein the tie plate attachment further includes at least one cap joined to the tie plate attachment over the at least one retention bore, the cap shaped to seal and fully enclose the irradiation target within the retention bore. 14. The structure of claim 11, wherein a plurality of irradiation targets are placed in the retention bore, at least a first irradiation target of the plurality being a first material and at least one of a second irradiation target of the plurality being a second material. 15. The structure of claim 1, wherein the outer structure has a cross-sectional thickness sufficient to encompass only a single row of fuel rods, and the cross-sectional thickness is along a transverse cross section of the nuclear fuel assembly. 16. The structure of claim 11, wherein the outer structure has a cross-sectional thickness sufficient to encompass only a single row of fuel rods, and the cross-sectional thickness is along a transverse cross section of the nuclear fuel assembly. 17. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being placed in the at least one retention bore such that at least a portion of the at least one irradiation target is embedded inside of the tie plate attachment,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the tie plate attachment further includes at least one lateral extension configured to connect the tie plate attachment to a channel surrounding the nuclear fuel assembly, the at least one lateral extension configured to hold the tie plate attachment in a constant axial position within the fuel assembly. 18. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore not passing entirely through the tie plate attachment such that a bottom and sides of the bore are continuously defined by the tie plate attachment, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being inside of and retained by the at least one retention bore,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the tie plate attachment further includes at least one lateral extension configured to connect the tie plate attachment to a channel surrounding the nuclear fuel assembly, the at least one lateral extension configured to hold the tie plate attachment in a constant axial position within the fuel assembly. 19. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being placed in the at least one retention bore such that at least a portion of the at least one irradiation target is embedded inside of the tie plate attachment,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the tie plate attachment further defines at least one hole shaped and positioned to permit a fuel rod of the nuclear fuel assembly to pass through the tie plate attachment and into the tie plate. 20. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore not passing entirely through the tie plate attachment such that a bottom and sides of the bore are continuously defined by the tie plate attachment, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being inside of and retained by the at least one retention bore,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the tie plate attachment further defines at least one hole shaped and positioned to permit a fuel rod of the nuclear fuel assembly to pass through the tie plate attachment and into the tie plate. 21. The structure of claim 19, wherein the at least one hole is shaped to seat against the fuel rod so as to lock the tie plate attachment against the tie plate. 22. The structure of claim 20, wherein the at least one hole is shaped to seat against the fuel rod so as to lock the tie plate attachment against the tie plate.