Patent Number: 
Section: claims

1. A method of creating desired isotopes in a commercial nuclear reactor generating heat for use in power production, the method comprising:operating the nuclear reactor to generate heat for use in power production,wherein the reactor includes an irradiation target holder in a core of the nuclear reactor, and the irradiation target holder being inaccessible from outside the reactor during the operating, wherein,the irradiation target holder directly contacts and is moveable within moderator of the nuclear reactor,the irradiation target holder is directly exposed to neutron flux from a plurality of fuel assemblies surrounding the irradiation target holder in the core during the operating,wherein the irradiation target holder is physically separate from all of the plurality of fuel assemblies,the irradiation target holder impermeably contains an irradiation target having a thermal neutron absorption cross section exceeding 1 barn and an atomic number less than 90, andthe operating irradiates the irradiation target holder with the neutron flux to produce a desired daughter product from the irradiation target. 2. The method of claim 1, further comprising:removing a startup source holder from the core; andinstalling the irradiation target holder in the core where the startup source holder was removed, wherein the removing and installing are performed during a non-operational period. 3. The method of claim 2, further comprising:retrieving the irradiation target holder from the core, wherein the retrieving is performed during a non-operational period. 4. The method of claim 3, wherein the retrieving includes moving at least one of the plurality of fuel assemblies directly adjacent to the irradiation target holder so as to expose and access the irradiation target holder. 5. The method of claim 2, wherein the removing withdraws at least a portion of the startup source holder from a penetration in a core plate supporting the plurality of fuel assemblies. 6. The method of claim 5,wherein the installing includes inserting at least a portion of the irradiation target holder into the penetration in the core plate previously occupied by the startup source holder and seating a fin of the irradiation target holder into an adjacent fuel casting on the core plate. 7. The method of claim 1, wherein the irradiation target is at least 0.1 kilograms of cobalt-59. 8. The method of claim 1, wherein the operating is performed for a plurality of months, and wherein the irradiation target holder is sealed inside the reactor during the operating, and wherein the irradiation target does not produce neutrons during the operating. 9. A method of creating desired isotopes in a commercial nuclear reactor generating heat for use in power production, the method comprising:removing a startup source holder from a startup holder position in a core of the nuclear reactor;installing an irradiation target holder in the startup holder position by inserting at least a portion of the irradiation target holder into a penetration in a core plate at a bottom of the core previously occupied by the startup source holder and seating a fin of the irradiation target holder into an adjacent fuel casting on the core plate;operating the nuclear reactor to generate heat for use in power production,wherein the reactor includes the irradiation target holder in the core of the nuclear reactor in the startup holder position directly exposed to neutron flux from a plurality of nuclear fuel assemblies surrounding the irradiation target holder and moderator in the core, and the irradiation target holder being inaccessible from outside the reactor during the operating, wherein,the irradiation target holder is physically separate from all the plurality of fuel assemblies and impermeably contains an irradiation target having a thermal neutron absorption cross section exceeding 1 barn and an atomic number less than 90, andthe operating irradiates the irradiation target holder with neutron flux to produce a desired daughter product from the irradiation target. 10. The method of claim 9, wherein the irradiation target is at least 0.1 kilograms of cobalt-59. 11. The method of claim 9, wherein the operating is performed for a plurality of months, and wherein the irradiation target holder is sealed inside the reactor during the operating, and wherein the irradiation target does not produce neutrons during the operating.