Patent Application
20110051874
1. Field
Example embodiments generally relate to isotopes and apparatuses and methods for production thereof in nuclear reactors.
2. Description of Related Art
Radioisotopes have a variety of medical and industrial applications stemming from their ability to emit discreet amounts and types of ionizing radiation and form useful daughter products. For example, radioisotopes are useful in cancer-related therapy, medical imaging and labeling technology, cancer and other disease diagnosis, and medical sterilization.
Radioisotopes having half-lives on the order of days are conventionally produced by bombarding stable parent isotopes in accelerators or low-power research reactors with neutrons on-site at medical or industrial facilities or at nearby production facilities. These radioisotopes are quickly transported due to the relatively quick decay time and the exact amounts of radioisotopes needed in particular applications. Further, on-site production of radioisotopes generally requires cumbersome and expensive irradiation and extraction equipment, which may be cost-, space-, and/or safety-prohibitive at end-use facilities.
Because of difficulties with production and the lifespan of short-term radioisotopes, demand for such radioisotopes may far outweigh supply, particularly for those radioisotopes having significant medical and industrial applications in persistent demand areas, such as cancer treatment.
Example embodiments are directed to methods of producing desired isotopes in commercial nuclear reactors and associated apparatuses. Example methods may utilize instrumentation tubes conventionally found in nuclear reactor vessels to expose irradiation targets to neutron flux found in the operating nuclear reactor. Short-term radioisotopes may be produced in the irradiation targets due to the flux. These short-term radioisotopes may then be relatively quickly and simply harvested by removing the irradiation targets from the instrumentation tube and reactor containment, without shutting down the reactor or requiring chemical extraction processes. The short-term radioisotopes may then be immediately transported to end-use facilities.
Example embodiments may include assemblies for retention and producing radioisotopes in nuclear reactors and instrumentation tubes thereof. Example embodiments may include one or more retention assemblies that contain one or more irradiation targets. Example embodiments may be useable with example delivery systems that permit delivery of irradiation targets. Example embodiments may be sized, shaped, fabricated, and otherwise configured to successfully move through example delivery systems and conventional instrumentation tubes while containing irradiation targets and desired isotopes produced therefrom.
Example embodiments will become more apparent by describing, in detail, the attached drawings, wherein like elements are represented by like reference numerals, which are given by way of illustration only and thus do not limit the example embodiments herein.
Detailed illustrative embodiments of example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only example embodiments set forth herein.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” or “fixed” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.).
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the language explicitly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially and concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
The instrumentation tubes 50 may terminate below the reactor pressure vessel 10 in the drywell 20. Conventionally, instrumentation tubes 50 may permit neutron detectors, and other types of detectors, to be inserted therein through an opening at a lower end in the drywell 20. These detectors may extend up through instrumentation tubes 50 to monitor conditions in the core 15. Examples of conventional monitor types include wide range detectors (WRNM), source range monitors (SRM), intermediate range monitors (IRM), and/or Local Power Range Monitors (LPRM).
Although vessel 10 is illustrated with components commonly found in a commercial Boiling Water Reactor, example embodiments and methods may be useable with several different types of reactors having instrumentation tubes 50 or other access tubes that extend into the reactor. For example, Pressurized Water Reactors, Heavy-Water Reactors, Graphite-Moderated Reactors, etc. having a power rating from below 100 Megawatts-electric to several Gigawatts-electric and having instrumentation tubes at several different positions from those shown in
Applicants have recognized that instrumentation tubes may be useable to quickly and constantly generate desired isotopes on a large-scale basis without the need for chemical or isotopic separation and/or waiting for reactor shutdown of commercial reactors. Example methods may include inserting irradiation targets into instrumentation tubes and exposing the irradiation targets to the core while operating, thereby exposing the irradiation targets to the neutron flux commonly encountered in the operating core. The core flux may convert a substantial portion of the irradiation targets to a useful radioisotope, including short-term radioisotopes useable in medical applications. Irradiation targets may then be withdrawn from the instrumentation tubes, even during ongoing operation of the core, and removed for medical and/or industrial use.
Example delivery systems are discussed below in conjunction with example embodiment irradiation target retention assemblies and irradiation targets useable therewith, which are described in detail later. It is understood that example embodiment irradiation target retention assemblies may be useable with other types of delivery systems than those described below.
An example cable 100 is illustrated in
As shown in
Referring to
An operator may configure first guide 400 and second guide 500 so that cable 100 may be advanced to a desired destination. For example, between loading/unloading area 2000 and instrumentation tube 50.
After configuring first and second guides 400 and 500, an operator may operate driving mechanism 300 to advance cable 100 through tubing 200a, first guide 400, and second tubing 200b to place first end 114 of driving portion 110 of cable 100 into the loading/unloading area 2000. An operator may advance cable 100 by controlling a worm gear in driving mechanism 300 that meshes with cable 100. The location of first end 114 of driving portion 110 of cable 100 may be tracked via markings 116 on cable 100. Alternatively, position of first end 114 of driving portion 110 of cable 100 may be known from information collected from a transducer that may be connected to drive mechanism 300.
After the cable 100 has been positioned in the loading/unloading area 2000 example embodiment retention assemblies 122 may then be connected to cable 100 as described below with reference to example embodiment retention assemblies. An operator may operate driving mechanism 300 to pull the cable from the loading/unloading area 2000 through tubing 200b and through first guide 400. The operator may then reconfigure first guide 400 to send cable 100 and example embodiment assemblies 122 to reactor pressure vessel 10. After first guide 400 is reconfigured, the operator may advance cable 100 through third tubing 200c, second guide 500, fourth tubing 200d, and into a desired instrumentation tube 50. Location of first end 114 of the driving portion 110 of cable 100 may be tracked via markings 116 on cable 100. In the alternative, position of first end 114 of driving portion 110 of cable 100 may be known from information collected from a transducer that may be connected to drive mechanism 300.
After cable 100 bearing example embodiment retention assemblies 122 has been advanced to the appropriate location within instrumentation tube 50, the operator may stop cable 100 in the instrumentation tube 50. At this point, irradiation targets within example embodiment irradiation target retention assemblies may be irradiated for the proper time in the nuclear reactor. After irradiation, the operator may operate driving mechanism 300 to pull cable 100 out of instrumentation tube 50, fourth tubing 200d, second guide 500, third tubing 200c, and/or first guide 400.
An operator may operate driving mechanism 300 to advance cable 100 through first guide 400, and second tubing 200b to place first end 114 of driving portion 110 of the cable 100 and example embodiment irradiation target retention assemblies 122 into the loading/unloading area 2000. Example assemblies 122 may be removed from cable 100 and stored in a transfer cask or another desired location. An example transfer cask may be made of lead, tungsten, and/or depleted uranium in order to adequately shield the irradiated targets. Attachment and detachment of example embodiment retention assemblies 122 may be facilitated by the use of cameras which may be placed in the loading/unloading area 2000 to allow an operator to visually inspect the equipment during operation.
An alternate delivery system includes use of a conventional Transverse In-core Probe (TIP) system 3000. A conventional TIP system 3000 is illustrated in
Because TIP system 3000 includes a tubing system 3200a, 3200b, 3200c, and 3200d and/or a guide 3500 for guiding a cable 3100 into an instrumentation tube 50, these systems may be used as an example delivery mechanism for example embodiment irradiation target retention assemblies and irradiation targets stored therein.
Cable 100 should be sized to function with existing tubing in example delivery systems and permit passage of example embodiment irradiation target retention assemblies. For example, the inner diameter of tubing 3200a, 3200b, etc. may be approximately 0.27 inches. Accordingly, cable 100 may be sized so that dimensions transverse to the cable 100 do not exceed 0.27 inches.
Example delivery systems being described, example embodiment irradiation target retention assemblies useable therewith are now described. It is understood that example retention assemblies may be configured/sized/shaped/etc. to interact with the example delivery systems discussed above, but example retention assemblies may also be used in other delivery systems and methods in order to be irradiated within a nuclear reactor.
Example embodiment irradiation target retention assembly 122a may include one or more bores 135 that extend partially into assembly 122a in an axial direction from a top end/face 138. Alternatively, bores 135 may extend into assembly 122a circumferentially or from other positions. Bores 135 may be arranged in any pattern and number, so long as the structural integrity of example embodiment irradiation target retention assemblies is preserved. Bores 135 themselves may have a variety of dimensions and shapes. For example, bores 135 may taper with distance from top face 138 and/or may have rounded bottoms and edges, etc. Example assembly 122a may be fabricated of a material that is configured to retain its structural integrity when exposed to flux encountered in an operating nuclear reactor. For example, example assembly 122a may be fabricated of zirconium alloy, stainless steel, aluminum, nickel alloy, silicon, graphite, and/or Inconel, etc.
Irradiation targets 130 may be inserted into one or more bores 135 in any desired number and/or pattern. Irradiation targets 130 may be in a variety of shapes and physical forms. For example, irradiation targets 130 may be small filings, rounded pellets, wires, liquids, and/or gasses. Irradiation targets 130 may be dimensioned to fit within bores 135, and/or bores 135 are shaped and dimensioned to contain irradiation targets 130. Additionally, example embodiment irradiation target retention assembly 122a may be fabricated from and/or internally contain irradiation target material, so as to become irradiation targets themselves. Irradiation targets 130 may further be sealed containers of a material designed to substantially maintain physical and neutronic properties when exposed to neutron flux within an operating reactor. The containers may contain a solid, liquid, and/or gaseous irradiation target and/or produced radioisotope so as to provide a third layer of containment for irradiation targets 130 within example embodiment retention assembly 122a.
A cap 131 may attach to top end/face 138 and seal irradiation targets 130 into bores 135. Cap 131 may attach to top end 138 in several known ways. For example, cap 131 may be directly welded to top face 138. Or, for example, cap 131 may screw onto top end 138 via threads on example retention assembly 122a and/or within individual bores 135. Although cap 131 is shown sized to cover a single bore 135, it is understood that cap may cover several or all bores 135, so as to seal irradiation targets 130 in multiple bores 135. For example, cap 131 may be annular and seal all bores 135 radially positioned in example retention assembly 122a but leave a middle bore 135 or hole 136 unsealed. In any of these attachments, cap 131 may retain irradiation targets 130 within a bore 135 and allow easy removal of cap 131 for containment and harvesting of desired solid, liquid, or gaseous radioisotopes and daughter products from irradiation targets 130.
As shown in
If a stack of example embodiment assemblies 122a are substantially flush against one another on cable 124, because bores 135 may not pass entirely through example assemblies 122a, the bottom surface of each assembly may be largely flat so as to facilitate a containing seal against another example assembly 122a stacked immediately below. In this way, irradiation targets 130 may be contained within bores 135 with or without an additional cap 131.
Example embodiment irradiation target retention assembly 122b has dimensions that enable it to be inserted into instrumentation tubes 50 (
Example embodiment irradiation target retention assembly 122b may be fabricated of a material that is configured to retain its structural integrity when exposed to flux encountered in an operating nuclear reactor. For example, example assembly 122b may be fabricated of aluminum, silicon, stainless steel, etc. Alternately, example embodiment irradiation target retention assembly 122b may be fabricated from a flexible material that permits some bending/deformation through bends in tubing 200a, b, c, d, including, for example, a high-temperature plastic. Still alternately, example embodiment irradiation target retention assembly 122b may be fabricated from an irradiation target material itself.
Example embodiment irradiation target retention assembly 122b may further include a first endcap 126 configured to join the assembly 122b to driving portion 110 of cable 100 (
Example embodiments of irradiation target retention assemblies 122 may permit several different types and phases of irradiation targets 130 to be placed in each assembly 122. Because several example assemblies 122a,b may be placed at precise axial levels within an instrumentation tube 50, it may be possible to provide a more exact amount/type of irradiation target 130 at a particular axial level within instrumentation tube 50. Because the axial flux profile may be known in the operating reactor, this may provide for more precise generation and measurement of useful radioisotopes in irradiation targets 130 placed within example embodiment irradiation target retention assemblies. Example embodiment irradiation target retention assembly being described, example irradiation targets useable therein are described below.
An irradiation target is a target that is irradiated for the purpose of generating radioisotopes. Accordingly, sensors, which may be irradiated by a nuclear reactor and which may generate radioisotopes, do not fall within the scope of term target as used herein since their purpose is to detect the state of the reactor rather than to generate radioisotopes.
Several different radioisotopes may be generated in example embodiments and example methods. Example embodiments and example methods may have a particular advantage in that they permit generation and harvesting of short-term radioisotopes in a relatively fast timescale compared to the half-lives of the produced radioisotopes, without shutting down a commercial reactor, a potentially costly process, and without hazardous and lengthy isotopic and/or chemical extraction processes. Although short-term radioisotopes having diagnostic and/or therapeutic applications are producible with example assemblies and methods, radioisotopes having industrial applications and/or long-lived half-lives may also be generated. Further, irradiation targets 130 may be chosen based on their relatively smaller neutron cross-section, so as to not interfere substantially with the nuclear chain reaction occurring in an operating commercial nuclear reactor core.
For example, it is known that Molybdenum-98 may be converted into Molybdenum-99, having a half-life of approximately 2.7 days when exposed to a particular amount of a neutron flux. In turn, Molybdenum-99 decays to Technetium-99m having a half-life of approximately 6 hours. Technetium-99m has several specialized medical uses, including medical imaging and cancer diagnosis, and a short-term half-life. Using irradiation targets 130 fabricated from Molybdnenum-98 and exposed to a neutron flux in an operating reactor based on the size of irradiation target 130, Molybdenum-99 and/or Technetium-99m may be generated and harvested in example embodiment assemblies and methods by determining the mass of the irradiation target containing Mo-98, the axial position of the target in the operational nuclear core, the axial profile of the operational nuclear core, and the amount of time of exposure of the irradiation target.
Table 1 below lists several short-term radioisotopes that may be generated in example methods using an appropriate irradiation target 130. The longest half-life of the listed short-term radioisotopes may be approximately 75 days. Given that reactor shutdown and spent fuel extraction may occur as infrequently as two years, with radioisotope extraction and harvesting from fuel requiring significant process and cool-down times, the radioisotopes listed below may not be viably produced and harvested from conventional spent nuclear fuel.
Table 1 is not a complete list of radioisotopes that may be produced in example embodiments and example methods but rather is illustrative of some radioisotopes useable with medical therapies including cancer treatment. With proper target selection, almost any radioisotope may be produced and harvested for use through example embodiments and methods.
Example embodiments thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied through routine experimentation and without further inventive activity. Variations are not to be regarded as departure from the spirit and scope of the exemplary embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
