Patent Number: 
Section: claims

1. A neutron source rod assembly for a nuclear reactor comprising;a neutron source positioning rodlet assembly having an upper coupling for connecting to a mounting assembly and an elongated substantially round body sized to slidingly fit within a guide thimble tube of a nuclear fuel assembly, the body extending a preselected distance from the upper coupling along an axis coinciding with an elongated dimension of the substantially round body and terminating in a lower coupling; anda source capsule assembly sealably enclosing a neutron source material, with the source capsule assembly configured as a separate component from the neutron source positioning rodlet assembly, structured to be boxed and shipped separately, sized to slidingly fit within the guide thimble tube and having an upper coupling configured to mate with the lower coupling of the neutron source positioning rodlet assembly and wherein the neutron source positioning rodlet assembly and the source capsule assembly are configured to be fixedly connected to each other at an assembly site and the preselected distance substantially extends from the mounting assembly to an elevation in a core of the nuclear reactor at which the neutron source material is to be situated. 2. The neutron source rod assembly of claim 1 wherein the neutron source positioning rodlet assembly lower coupling and the source capsule assembly upper coupling are mechanical couplings that are configured to mate with each other. 3. The neutron source rod assembly of claim 2 wherein the neutron source positioning rodlet assembly lower coupling is one of either a male or female threaded coupling and the source capsule assembly upper coupling is another of the male or female threaded coupling that the one of either the male or female threaded coupling on the neutron source positioning rodlet assembly lower coupling will mate with. 4. The neutron source rod assembly of claim 1 wherein the source capsule assembly has an elongated axial dimension that is sufficient to contain sufficient neutron source material to provide the neutrons required for a specified X-core source range detector count rate during startup for the nuclear reactor, but is substantially shorter than the elongated dimension of the neutron source positioning rodlet assembly. 5. The neutron source rod assembly of claim 1 wherein the neutron source positioning rodlet assembly is a solid rod. 6. The neutron source rod assembly of claim 1 wherein the neutron source positioning rodlet assembly is at least in part formed from a hollow tube that is capped at each end. 7. The neutron source rod assembly of claim 6 wherein the neutron source material is a primary neutron source and the hollow tube contains a secondary neutron source material. 8. The neutron source rod assembly of claim 1 wherein the lower coupling of the neutron source positioning rodlet assembly and the upper coupling of the source capsule assembly lock together when fully connected. 9. The neutron source rod assembly of claim 8 wherein the lower coupling of the neutron source positioning rodlet assembly and the upper coupling of the source capsule assembly are threaded couplings and lock together when fully tightened. 10. A method of manufacturing a neutron source rod assembly comprising a mounting assembly, a plurality of thimble plug rodlets or a plurality of burnable neutron poison rodlets, a neutron source positioning rodlet assembly and a source capsule assembly, comprising the steps of:manufacturing the mounting assembly, the plurality of thimble plug rodlets or the plurality of burnable neutron poison rodlets and the neutron source positioning rodlet assembly in a first manufacturing facility remote from an assembly site at which the neutron source rod assembly is intended to inserted into a fuel assembly, wherein the neutron source positioning rodlet assembly comprises an upper coupling for connecting to the mounting assembly and an elongated substantially round body sized to slidingly fit within a guide thimble tube of a nuclear fuel assembly, the body extending a preselected distance from the upper coupling along an axis coinciding with an elongated dimension of the substantially round body and terminating in a lower coupling;manufacturing the source capsule assembly in a second manufacturing facility remote from the assembly site, the source capsule assembly sealably enclosing a neutron source material, with the source capsule assembly sized to slidingly fit within the guide thimble tube at the assembly site and having an upper coupling configured to mate with the lower coupling of the neutron source positioning rodlet assembly and wherein the preselected distance substantially extends from the mounting assembly to an elevation in the fuel assembly at which the neutron source material is to be situated;shipping the mounting assembly, the plurality of thimble plug rodlets or the plurality of burnable neutron poison rodlets and the neutron source positioning rodlet assembly to the assembly site;shipping the source capsule assembly to the assembly site;assembling the source capsule assembly to the lower coupling of the neutron source positioning rodlet assembly at the assembly site; andinserting the neutron source rod assembly into a fuel assembly at the assembly site. 11. The method of claim 10 wherein the assembly site is a nuclear reactor at which the neutron source rod assembly is used. 12. The method of claim 10 wherein the assembly site is a nuclear fuel assembly manufacturing facility. 13. The method of claim 10 wherein the mounting assembly, the plurality of thimble plug rodlets or the plurality of burnable neutron poison rodlets and the neutron source positioning rodlet assembly are assembled together at the first manufacturing facility. 14. The method of claim 10 wherein the mounting assembly, the plurality of thimble plug rodlets or the plurality of burnable neutron poison rodlets and the neutron source positioning rodlet assembly are assembled together at the assembly site.