Techniques for heat dissipation from a nuclear transmutation target

Abstract

Techniques are described for dissipating heat from a capsule placed within a nuclear reactor. A capsule may comprise a target material that includes one or more isotopes that are to be transmuted by neutrons in the reactor, and a housing that holds the target material. The techniques allow for improved heat dissipation from the capsule and / or its contents when the capsule is arranged within a nuclear reactor.

Description

Attorney Docket No.: 226194-700620 / PCTTECHNIQUES FOR HEAT DISSIPATION FROM A NUCLEAR TRANSMUTATION TARGET CROSS-REFERENCE

[0001] The present application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 63 / 776,589, filed March 24, 2025, titled “Techniques for Heat Dissipation from a Nuclear Transmutation Target,” and U.S. Provisional Patent Application No. 63 / 929,396, filed December 2, 2025, titled “Techniques for Heat Dissipation from a Nuclear Transmutation Target,” each of which is hereby incorporated by reference in its entirety.BACKGROUND

[0002] The abundance of neutrons makes a nuclear reactor an attractive location to produce certain desirable radioisotopes. A number of radioisotopes may be produced directly or indirectly as a result of neutron interactions by leaving a suitable target material inside a reactor. While the target material is in the reactor, the ambient neutrons in the reactor may produce reactions with the target material isotope(s) to produce other isotopes. The isotope(s) produced may themselves be desirable or may radioactively decay into one or more other desirable isotopes.SUMMARY

[0003] According to some aspects, the techniques described herein relate to a capsule configured to be inserted into a nuclear reactor, the capsule including: a housing; a target material arranged within the housing; and a thermal transport material arranged within the housing and arranged at least partially between the target material and the housing.

[0004] According to some aspects, the techniques described herein relate to a method including: inserting a capsule into a thimble tube of a nuclear reactor, the capsule including a target material arranged within a housing; leaving the capsule in the thimble tube of the nuclear reactor for a first time period during which the housing of the capsule contacts the thimble tube and at least some of a first isotope within the target material is transmuted into a second isotope; and removing the capsule from the nuclear reactor.Attorney Docket No.: 226194-700620 / PCT

[0005] The foregoing apparatus and method embodiments may be implemented with any suitable combination of aspects, features, and acts described above or in further detail below. These and other aspects, embodiments, and features of the present teachings can be more fully understood from the following description in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF DRAWINGS

[0006] Various aspects and embodiments will be described with reference to the following figures. It should be appreciated that the figures are not necessarily drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing.

[0007] FIG. 1A is a schematic of a system in which aspects of the present disclosure may be practiced, according to some embodiments;

[0008] FIG. IB is a cross-sectional view of a capsule inserted into a thimble tube of a reactor, according to some embodiments;

[0009] FIG. 1C is a cross-sectional view of a coupled series of capsules inserted into a thimble tube of a reactor, according to some embodiments;

[0010] FIG. 2 is a cross-sectional view of a coupled series of capsules inserted into a thimble tube of a reactor and arranged to contact the thimble tube, according to some embodiments;

[0011] FIG. 3 is a cross-sectional view of a capsule comprising a thermal transport material and a target material, according to some embodiments;

[0012] FIG. 4 depicts a system for backfdling a thimble tube with a gas, according to some embodiments; and

[0013] FIG. 5 is a flowchart of a method of transmuting one or more isotopes while dissipating heat from a capsule placed within a nuclear reactor, according to some embodiments.Attorney Docket No.: 226194-700620 / PCTDETAILED DESCRIPTION

[0014] As described above, the abundance of neutrons makes a nuclear reactor an attractive location to produce certain desirable radioisotopes. Radioisotope production in fission reactors can, for example, be based on neutron capture in a target material, either by activation or by generation of radioisotopes from fission of the target material by bombardment with thermal neutrons. For example, molybdenum-99 and lutetium-177 are often produced in research reactors for medical usage. Another desirable isotope is actinium -225, which can be produced by using a radium -226 target material. If neutrons or gamma rays have a kinetic energy of at least 6.4MeV, they will initiate an (n,2n) or (g,n) reaction that converts radium-226 into radium-225, which then decays naturally into actinium -225.

[0015] Many reactions that take place during such an operation in a reactor produce additional neutrons and / or other particles that deposit energy in the target material and / or other nearby structures. As a result, some reactions that can be performed in a reactor generate heat within a target material and / or within a structure in which the target material is arranged. For example, in the (g,n) reaction mentioned above the target nucleus absorbs a gamma ray, then emits a neutron. The neutron may scatter, depositing energy in the target material and / or other nearby structures, thereby heating them. In some cases, a target material for reactions in a nuclear reactors may include isotopes other than the direct targets that in some way enhance or otherwise alter the processes that produce a desired radioisotope in the target. These additional reactions can also generate heat within the target material.

[0016] In some cases, the amount of heating of a target material and / or nearby structures (e.g., a capsule holding the target material) may exceed tolerances, such as safety limits. These limits may be set by reactor engineers, or may relate to safe limits for the target material and / or nearby structures. For example, a capsule holding the target material may be at risk of melting, deforming or bursting above a particular temperature. These limits may place a ceiling on the amount of a desired radioisotope that can be produced in a given process. That is, there may be situations where a particular amount of a desired radioisotope may be produced in principle, but the amount of heating and associated limits mean that the process must be engineered to produce lessAttorney Docket No.: 226194-700620 / PCTthan the maximum possible, which is inefficient and in some cases may be wasteful of expensive target materials.

[0017] The inventors have recognized and appreciated techniques for dissipating heat from a capsule placed within a nuclear reactor. As described further below, the capsule generally comprises a target material that includes one or more isotopes that are to be transmuted by neutrons in the reactor, and a housing that holds the target material. The techniques described herein allow for improved heat dissipation from the capsule and / or its contents when the capsule is arranged within a nuclear reactor.

[0018] According to some embodiments, the heat dissipation techniques described herein include providing a thermal transport material within the capsule that improves heat transfer from the target material to the housing of the capsule. The thermal transport material may be arranged, for example, between the target material and the housing. In some embodiments, the thermal transport material is, or comprises a powder such as aluminum powder or diamond powder. In some embodiments, the thermal transport material is a solid material, such as aluminum or diamond. Preferably, the thermal transport material has a low neutron cross section so that it does not significantly impede neutrons from reaching the target material.

[0019] According to some embodiments, the heat dissipation techniques described herein include arranging a capsule comprising a target material within a nuclear reactor so that it touches a structure within the reactor, such as the inner surface of a thimble tube. While ensuring this type of contact may be challenging for a single capsule, in some cases a target may comprise a series of coupled capsules. By arranging the coupling between capsules to introduce a slight deviation from a straight coupling, the total width of the series of capsules may be made at least as wide as a structure in which the series of capsules is to be inserted. For example, a series of capsules may be coupled together with a slight ‘kink’ in one or more of the couplings so that the width of the series of capsules is slightly wider than a thimble tube into which the series of capsules is to be inserted. As a result, it is highly likely that at least one of the capsules in the series of capsules will contact the inner surface of the thimble tube when the series of capsules is inserted into the thimble tube. This contact will increase heat dissipation from theAttorney Docket No.: 226194-700620 / PCTcapsule by allowing conductive heat transfer into the thimble tube and the surrounding water.

[0020] According to some embodiments, the heat dissipation techniques described herein include backfdling a structure in which a capsule is arranged with a gas that has a desirable thermal conductivity. Preferably, the gas also has a low neutron cross section so that it does not significantly impede neutrons from reaching the target material. For example, helium gas (e.g., helium-4 gas) has a much greater thermal conductivity than air (e.g., around 0.15W / mK for helium-4 vs 0.025 W / mK for air) and is essentially transparent to neutrons. As such, backfilling a thimble tube with helium gas would dramatically increase heat dissipation from capsule arranged within the thimble tube by allowing much more heat transfer through the thimble tube than would occur with air in the tube. In some cases, the improved thermal conductivity of the area around the capsule may cause heat within the capsule itself to be more uniform.

[0021] Following below are more detailed descriptions of various concepts related to, and embodiments of, techniques for dissipating heat from a nuclear transmutation target. It should be appreciated that various aspects described herein may be implemented in any of numerous ways. Examples of specific implementations are provided herein for illustrative purposes only. In addition, the various aspects described in the embodiments below may be used alone or in any combination, and are not limited to the combinations explicitly described herein.

[0022] FIG. 1A is a schematic of a system in which aspects of the present disclosure may be practiced, according to some embodiments. In the example of FIG.1A, system 100 includes a portion of a nuclear reactor 120 (e.g., a fission reactor) comprising water 125 and a guide tube 114 that allows for insertion of a capsule 105 into the reactor. The guide tube 114 may guide the capsule 105 into the reactor by allowing the capsule to be passed through the seal table 107 and through the guide tube into the thimble tube 115 and thereby into a portion of the reactor containing neutron flux.Motion of the capsule 105 is produced by a drive unit 110 coupled to the capsule 105 via cable 111. Operating the drive unit 110 feeds the capsule 105 through the guide tube by unspooling the cable 111, which feeds the cable into the guide tube, pushing the capsule inward. In some embodiments, the cable 111 is a metal cable (e.g., titanium cable) thatAttorney Docket No.: 226194-700620 / PCTis atached to the capsule 105. In some embodiments, the drive unit 110 may be a pneumatic loading system.

[0023] The capsule 105 may be inserted through the seal table, which separates atmospheric pressure outside the guide tube and reactor from inside the guide tube and reactor where the pressure may be over lOOOpsi. The capsule may be inserted directly into the guide tube through a thimble or port, or may be inserted into a vessel (e.g., a thimble) that is directed into the reactor as described above. As described further below, in some embodiments a series of coupled capsules may be inserted through the seal table and driven into the guide tube 114 (e.g., through a keyway). In some cases, the capsules may be inserted through a manifold, followed by the seal table.

[0024] According to some embodiments, the thimble tube 115 may be a flux thimble guide tube that is also used for inserting measurement probes and other devices used routinely in commercial fission reactors. However, it may be appreciated that this process of inserting a capsule into a reactor may be different at a research reactor versus a commercial reactor, and as such the example of FIG. 1A may not apply to all implementations. Any references to guide tubes or thimble tubes herein are not intended to be limited to any particular tube design, and may encompass any type of tube utilized in a reactor to insert a target object into a portion of the reactor containing neutron flux.

[0025] FIG. IB is a cross-sectional view of the capsule 105 when inserted into the thimble tube 115. In the example of FIG. IB, the capsule 105 comprises a housing 151 and interior 152. The interior 152 of the housing 151 may comprise a target material and optionally may comprise additional materials including a converter material and / or a thermal transport material, described further below. In some cases, additional layers of housing may be provided in addition to housing 151 to further encapsulate the target material within the interior of the housing 151 and / or to separate materials within different encapsulations. For instance, the capsule 105 may comprise a plurality of nested housings that each encapsulate one or more of the housings and the target material.

[0026] FIG. 1C depicts an example of a plurality of capsules 105 coupled together in series and arranged within the thimble tube 115 (which as noted above may be a thimble tube). Each of the capsules 105 shown in FIG. 1C comprise a housing 151 andAttorney Docket No.: 226194-700620 / PCTinterior 152 as shown in FIG. IB. The interior of each of these capsules may comprise a target material and optionally may comprise additional materials including a converter material and / or a thermal transport material, described further below.

[0027] According to some embodiments, housing 151 may be a cylinder, or may be substantially cylindrical. For instance, the cross-sectional view shown in FIG. 1A may be representative of all cross-sections along the same axis, such that the capsule has rotational symmetry around its long axis. However, other cylindrical shapes may also be envisioned. The housing of the capsule may have rounded edges as shown in the drawing, yet the capsule may still be considered, in at least some embodiments, to be cylindrical for the purposes of this disclosure. Other suitable shapes for a capsule may include elongated beads or a toroid.

[0028] According to some embodiments, housing 151 may be formed from, or may comprise, a metal or metal alloy. In some embodiments, housing 151 is formed from titanium, comprises titanium, or consists essentially of titanium. In some embodiments, housing 151 is formed from a zirconium alloy, comprises a zirconium alloy, or consists essentially of zirconium alloy. The housing 151 may in some embodiments comprise aluminum, in addition to titanium or a zirconium alloy as noted above. In some embodiments, the housing 151 may be formed from carbon (e.g., diamond).

[0029] As used herein, the term “capsule” refers to any encapsulated vessel in which a target material is arranged, and the term is not intended to suggest any particular size or shape of this vessel. As such, while embodiments depicted in the drawings include a cylindrical capsule, it will be appreciated that the capsule may in general have any suitable size and / or shape so long as the capsule is suitable for insertion into an environment containing neutrons sufficient to initiate a desired transmutation process.

[0030] According to some embodiments, cable 111 may be formed from, or may comprise, a metal or metal alloy. In some embodiments, cable 111 is formed from titanium, comprises titanium, or consists essentially of titanium. Cable 111 may in some cases be inserted into a portion of the housing 151 of the capsule 105 and attached there with a fastener, by crimping the capsule onto the cable, and / or by some other suitable coupling method.Attorney Docket No.: 226194-700620 / PCT

[0031] The width (e.g. diameter) of the capsule 105 is shown in FIG. IB as width 105w. In some embodiments, the width 105w of the capsule 105 is greater than or equal to 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 10 mm, 15 mm, or 25 mm. In some embodiments, the width 105w of the capsule 105 is less than or equal to 30 mm, 25 mm, 15 mm, 10 mm, 6.5 mm, 6 mm, 5.5 mm, 5 mm, 4.5 mm, 4 mm, 3.5 mm, 3 mm, or 2.5 mm. Any suitable combinations of the above-referenced ranges are also possible (e.g., the width 105w of the capsule 105 is greater than or equal to 4.5 mm and less than or equal to 5 mm).

[0032] The width (e.g. diameter) of the thimble tube 115 is shown in FIG. IB as width 115w. In some embodiments, the width 115w of the thimble tube 115 is greater than or equal to 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 10 mm, 15 mm, or 25 mm. In some embodiments, the width 115w of the thimble tube 115 is less than or equal to 30 mm, 25 mm, 15 mm, 10 mm, 7.5 mm, 7 mm, 6.5 mm, 6 mm, 5.5 mm, 5 mm, 4.5 mm, or 4 mm. Any suitable combinations of the above-referenced ranges are also possible (e.g., the width 115w of the thimble tube 115 is greater than or equal to 5 mm and less than or equal to 5.5 mm).

[0033] According to some embodiments, housing 151 may include multiple elements, such as metal elements, joined together via a joint, and / or joined through a process such as welding, brazing, crimping, pressing, threading and / or soldering. In some cases, for instance, a target material, and optionally other materials such as a converter material and / or a thermal transport material, may be inserted into an open end of a vessel, then a plug or cap is press fit and / or welded to the vessel to produce housing 151 and capsule 105 as shown in FIGs. 1A-1B.

[0034] As such, in some cases a welding seam may be present on the exterior surface of housing 151, although in general it may be desirable to make this welding seam as invisible as possible to ensure the capsule can be inserted and removed from a reactor without snagging or otherwise limiting movement of the capsule during its motion.

[0035] According to some embodiments, a target material arranged within the interior 152 of a capsule may include any substance or substances that contain one or more isotopes to be transmuted (whether directly or indirectly) through interactions withAttorney Docket No.: 226194-700620 / PCTneutrons in the nuclear reactor. Transmutation may include any one or more of neutron capture, beta decay after neutron capture, fission, (n,p) reactions, (g,n) reactions, (n,g) reactions, (n,a) reactions, (n,2n) reactions, neutron scattering, or combinations thereof.

[0036] In each of the examples of FIGs. 1A-1C, according to some embodiments, the target material may be, or may comprise, isotopes such as, but not limited to, uranium-235, gadolinium- 160, copper-63, copper-66, molybdenum-98, cobalt-59, iridium- 191, tellurium- 130, radium-226, lutetium-176, and / or ytterbium- 176.Compounds of any such isotopes may also be provided in the target material. For example, the target material may comprise a chloride, nitride, nitrate, hydroxide, fluoride, bromide, carbonate, sulfate, and / or oxide of any one or more isotopes.Additionally, or alternatively, any such isotopes may be provided in the target material as a pure element. As noted above and described further below, a capsule 105 may also contain other components in addition to the target material, such as a thermal transport material and / or a converter material.

[0037] As shown in FIG. 1C, in some embodiments multiple capsules 105 may be coupled together via couplings 155. The couplings may in some cases be inserted into a portion of the housing 151 of the capsule 105 and attached there with a joint, a fastener, by crimping the capsule onto the cable, and / or by some other suitable coupling method. In some embodiments, the couplings are formed from the same material as cable 111 (e.g., titanium). The couplings 155 may be formed from, or may comprise, a metal or metal alloy. In some embodiments, the couplings comprise opposing ball and socket joints.

[0038] In some embodiments, the couplings 155 between the capsules 105 may be sufficiently flexible to allow the relative orientation of adjacent capsules to shift. As described above, the heat dissipation techniques described herein include arranging a capsule comprising a target material within a nuclear reactor so that it touches a structure within the reactor, such as the inner surface of a thimble tube. In some embodiments, this configuration may be achieved, at least in part, by configuring the couplings 155 so that they provide a slightly kinked coupling between adjacent capsules 105. An example of such a configuration is shown in FIG. 2.Attorney Docket No.: 226194-700620 / PCT

[0039] In the example of FIG. 2, multiple capsules 105 are coupled together and inserted into the thimble tube 115 of the reactor shown in FIG. 1A. The couplings 155 connect adjacent capsules 105 together, and are configured such that adjacent capsules are not oriented in the same direction. As a result, when the series of capsules is inserted into the thimble tube 115, one or more of the capsules may contact the interior surface of the guide tube. As shown in FIG. 2, for example, two of the capsules 105 in the depicted series of capsules contact the thimble tube 115 at the highlighted points 201.

[0040] As described above, heat generated in the capsules 105 may be much more effectively dissipated from the capsules through the guide tube wall than through the space between the capsule and guide tube. While the water 125 in the reactor is generally expected to be at a high temperature (e.g., at 302°C), the capsule may be nonetheless heated to above this temperature through the isotopic transmutations and / or other reactions taking place within the capsule. Without an effective way for this heat to dissipate from the capsule, the temperature in the capsule may continue to rise, potentially risking hitting a safety limit or other limit. By allowing the capsule(s) to contact the thimble tube 115, however, a more thermally conductive path is provided into the guide tube than through the gas surrounding the target alone. Moreover, since there is such a large body of water 125 in the reactor (in particular, large compared to the size of the capsule 105), any heat transferred from the capsule into the water via the guide tube would not be expected to change the temperature of the water by a measurable amount.

[0041] FIG. 3 is a cross-sectional view of a capsule comprising a thermal transport material and a target material, according to some embodiments. The capsule 105 shown in FIG. 3 may be used in the example of FIGs. 1A-1C and FIG. 2, and inserted into a reactor as described above in relation to FIG. 1 A. Any of the above-described embodiments for capsule 105 also apply to the example of FIG. 3. In the example of FIG. 3, the capsule 105 comprises a thermal transport material 302, a target material 303, both of which are encapsulated by the housing 151. In some embodiments, the thermal transport material 302 and target material 303 may be hermetically sealed within the housing 151. Any of the configurations of capsule 105 described above in relation to the configuration of the housing 151 and other aspects of the capsule may also be applied toAttorney Docket No.: 226194-700620 / PCTthe capsule shown in FIG. 3, which differs from the capsule shown in FIGs. 1A-1C and FIG. 2 only in providing an illustrative example of the interior 152 of the capsule 105.

[0042] As with the example of FIGs. 1A-1C and FIG. 2, the target material 303 may include any substance or substances that contain one or more isotopes to be transmuted (whether directly or indirectly) through interactions with neutrons in the nuclear reactor. Transmutation may include any one or more of neutron capture, beta decay after neutron capture, fission, (n,p) reactions, (n,a) reactions, (g,n) reactions, (n,g) reactions, (n,2n) reactions, neutron scattering, or combinations thereof.

[0043] According to some embodiments, the target material 303 may be, or may comprise, isotopes such as, but not limited to, uranium -235, gadolinium- 160, copper-63, copper-66, molybdenum-98, cobalt-59, iridium-191, tellurium- 130, radium-226, lutetium-176, and / or ytterbium- 176. Compounds of any such isotopes may also be provided in the target material. For example, the target material may comprise a chloride, nitride, nitrate, hydroxide, fluoride, bromide, carbonate, sulfate, and / or oxide of any one or more isotopes (e.g., radium chloride). Additionally, or alternatively, any such isotopes may be provided in the target material as a pure element.

[0044] According to some embodiments, the target material 303 is housed within a vessel that holds the target material. In some cases, the vessel may comprise quartz (SiCh), soda lime, a ceramic, and / or a metal. In some embodiments, for instance, the target material 303 may be a solution (e.g., a radium solution) held within a glass vial. A vessel (e.g., vial or tube) containing the target material may have a thickness of between 10 pm and 200 pm, such as 100 pm (e.g., a glass tube), although may in general have a thickness between 10 pm and 1 mm.

[0045] In some embodiments, the target material 303 comprises one or more radium compounds such as, but not limited to, radium chloride, radium nitride, radium nitrate, radium hydroxide, radium fluoride, radium bromide, radium carbonate, radium sulfate, radium oxide, radium fluoride or combinations thereof. Any one or more of such radium compounds may be included in the target material 303, and each may be isotopically enriched with radium-226 according to the above levels of radium-226 isotopic enrichment. For instance, the target material 303 may comprise radium chloride having a radium-226 isotopic enrichment of greater than or equal to 90% and less than orAttorney Docket No.: 226194-700620 / PCTequal to 100%, with any other suitable combinations of the above-referenced ranges being also possible. As described above, in some cases a radium compound may be provided as a solution. As one example, the target material 303 may comprise an aqueous solution of radium chloride, wherein the radium chloride in the solution has a radium-226 isotopic enrichment of greater than or equal to 98% and less than or equal to 100%, with any other suitable combinations of the above-referenced ranges being also possible. An amount of isotopic enrichment of the target material 303 according to any of the above ranges may for instance be measured via a method such as nuclear magnetic resonance (NMR), mass spectrometry, gamma spectroscopy, beta spectroscopy, alpha spectroscopy, or x-ray spectroscopy.

[0046] References here to an “isotopically enriched” material are not intended to imply that isotopic separation of isotopes necessarily be performed to produce that material, although in some cases it may. Rather, this term along with references to “isotopic enrichment” of a material are intended only to refer to the amount of particular isotopes in the material, not how that material was produced. For instance, extraction of deuterium from sea water may comprise isotopic separation. Some methods of extracting radium-226 may also comprise isotopic separation. However, in some cases radium-226 may be obtained from natural sources of radium that include both radium-226 and radium-228. Since radium -228 has a much shorter half-life than radium-226, the passage of time may produce a natural source much more abundant in radium-226 than radium-228 without any isotopic separation being performed.

[0047] In the example of FIG. 3, thermal transport material 302 is arranged between the target material 303 and the housing 151. While in the example of FIG. 3 the thermal transport material 302 is shown fully surrounding the target material 303, in general the thermal transport material need not be arranged as such, so long as it provides a thermal pathway from the target material to the housing. For example, the thermal transport material may be arranged at least partially between the target material and the housing.

[0048] According to some embodiments, the thermal transport material 302 may be, or may comprise, a powder. A powder may be easily arranged within the capsule 105 to provide a thermal pathway from the target material 303 to the housing 151.Attorney Docket No.: 226194-700620 / PCTPreferably, the thermal transport material 302 has a high thermal conductivity to allow for effective heat transfer. In some embodiments, the thermal transport material 302 comprises, or consists of, aluminum powder or diamond powder. In some embodiments, the thermal transport material 302 comprises, or consists of, a powder and a gas. The gas may be different from air, and may desirably be a gas with a comparatively high thermal conductivity, such as helium. For instance, the thermal transport material 302 may comprise, or consist of, aluminum powder or diamond powder within a helium gas. As one example, the capsule 105 may be sealed with the powder arranged around the target material and inside the housing 151 and open space within the capsule may be fdled with a gas (e.g., helium gas).

[0049] In some embodiments, the thermal transport material 302 may comprise, or may consist of, a powder having a thermal conductivity of greater than or equal to 1 W / mK, 5 W / mK, 20 W / mK, 50 W / mK, 100 W / mK, 250 W / mK, 500 W / mK, 1000 W / mK, or 2000 W / mK. In some embodiments, the thermal transport material 302 may comprise, or may consist of, a powder having a thermal conductivity of less than or equal to 2500 W / mK, 1500 W / mK, 1000 W / mK, 500 W / mK, 250 W / mK, 100 W / mK, 50 W / mK, 20 W / mK, 10 W / mK or 5 W / mK. Any suitable combinations of the abovereferenced ranges are also possible (e.g., the thermal transport material 302 may comprise, or may consist of, a powder having a thermal conductivity of greater than or equal to 1 W / mK and less than or equal to 500 W / mK, or greater than or equal to 2000 W / mK and less than or equal to 2500 W / mK).

[0050] According to some embodiments, the thermal transport material 302 may be, or may comprise, a solid. In some implementations, the thermal transport material 302 may be provided, in whole or in part, as a solid element arranged between the target material 303 and the housing 151. For instance, in implementations in which the housing has a cylindrical interior, the thermal transport material 302 may be provided as an annular cylinder, where the target material 303 is arranged within the interior of the thermal transport material 302. Such a cylinder may be fabricated through electrical discharge machining (EDM), for instance. In some embodiments, the thermal transport material 302 comprises, or consists of, solid aluminum or solid diamond (e.g., sinteredAttorney Docket No.: 226194-700620 / PCTdiamond powder). The thermal transport material may be provided as a solid in any form, including a solid cylinder, cone, beads, tubes, etc.

[0051] In some embodiments, the thermal transport material 302 may have a higher coefficient of thermal expansion (CTE) than the CTE of the housing 151. As a result, when the capsule 105 heats up, the thermal transport material 302 may be expected to thermally expand at a faster rate than the housing, leading to the thermal transport material occupying more space within the housing at a comparatively higher temperature than at a comparatively lower temperature. This configuration may be advantageous for at least the following reasons.

[0052] First, the thermal transport material 302 may be provided as a solid that is smaller than the interior of the housing 151 and can therefore be more easily inserted into the housing 151, or a portion thereof, at room temperature. However, when the capsule 105 is heated, the thermal transport material 302 may expand more than the housing and fill up the empty space within the interior of the capsule, thereby providing intimate contact between the target material 303 and the thermal transport material, and between the thermal transport material and the housing 151 and allowing heat to be effectively transferred outward. Second, a solid thermal transport material 302 provided in this manner may provide structural support to the target material 303, effectively reducing internal pressure in the capsule and allowing a greater pressure to be built up within the target material than might otherwise be desirable in the absence of the solid thermal transport material in intimate contact with the target material (and / or a vessel in which the target material is arranged).

[0053] According to some embodiments, the thermal transport material 302 may be, or may comprise, a liquid. In some embodiments, the thermal transport material 302 comprises, or consists of, liquid mercury or liquid gallium.

[0054] According to some embodiments, the capsule 105 may comprise a converter material in addition to the thermal transport material 302. The converter material may be configured to alter the neutron spectrum that would otherwise be incident on the target material 303 by providing isotopes that react with neutrons to produce neutrons of a different energy. For example, the converter material may produce fast neutrons from thermal neutrons via one or more reactions initiated by aAttorney Docket No.: 226194-700620 / PCTthermal neutron in the converter material. Additionally, or alternatively, the converter material may produce neutrons from incident gamma rays (e.g., via (g,n) reactions). In some embodiments, the converter material is mixed with the target material 303 (e.g., inside a vessel). In some embodiments, the converter material is arranged exterior to the target material 303, such as between the thermal transport material 302 and the target material.

[0055] FIG. 4 depicts a system for backfdling a guide tube with a gas, according to some embodiments. As described above, the heat dissipation techniques described herein include backfilling a structure in which a capsule comprising a target material is arranged with a gas that has a desirable thermal conductivity. System 400 depicts an example of an apparatus that can be operated to backfill a guide tube of a reactor with a gas, according to some embodiments.

[0056] In the example of FIG. 4, a manifold 410 is arranged over the end of thimble tube 115 (or a different part of the structure such as the key way or seal table tube), which is coupled through the manifold to a vacuum pump 420 and to a gas source 430. In some embodiments, the source of gas is a source of helium gas, such as helium -4 gas. In the example of FIG. 4, the cable 111 also passes through the manifold 410. The manifold may be seal table 107, or a different structure.

[0057] The manifold 410 is configured to provide a vacuum seal over the thimble tube 115 to allow the guide tube to be pumped to low pressure by operating the vacuum pump 420. In operation, the thimble tube may be closed via a valve on manifold 410, and a valve on the manifold may then be opened to allow the vacuum pump to be operated to evacuate the thimble tube 115 down to low pressure, such as below 1 Torr. The vacuum pump may then be shut off and the valve on the manifold connected to the vacuum pump closed. Another valve on the manifold connected to the gas source 430 may then be opened to allow gas to flow from the gas source 430 into the thimble tube 115. If desired, this process of pumping and backfilling can be repeated one or more times to obtain a very high concentration of the gas from the gas source 430 in the thimble tube 115. In general, backfilling of the thimble tube with the gas is desirably completed before a capsule is inserted into the thimble tube. In some embodiments, theAttorney Docket No.: 226194-700620 / PCTgas source 430 includes a pump and / or other components for conveying gas into the thimble tube 115 from a gas storage container.

[0058] As described above, it may be particularly desirable for gas source 430 to backfdl the thimble tube 115 with helium-4 gas because it is essentially transparent to neutrons and because its thermal conductivity is around six times that of air. Although, any gas that has a thermal conductivity higher than air may in principle be provided by the gas source 430. Irrespective of the type of gas used, by backfdling the thimble tube 115 with a gas that has a thermal conductivity higher than air, dissipation of heat from the capsule 105 into the water 125 will be increased.

[0059] In some embodiments, the gas provided by the gas source 430 may comprise both helium gas and hydrogen gas. A mixture of hydrogen and helium gas (whether helium-4 or otherwise) may increase the thermal conductivity of the gas provided by the gas source compared with a pure helium-4 gas.

[0060] In some embodiments, the gas provided by the gas source 430 may comprise hydrogen gas in an amount greater than or equal to 2%, 3%, 4%, 5%, 6%, 7% or 8% by volume. In some embodiments, the gas provided by the gas source 430 may comprise hydrogen gas in an amount less than or equal to 10%, 9%, 8%, 7%, 6%, 5% or 4% by volume. Any suitable combinations of the above-referenced ranges are also possible (e.g., the gas provided by the gas source 430 may comprise hydrogen gas in an amount greater than or equal to 5% by volume and less than or equal to 10% by volume, or greater than or equal to 7% by volume and less than or equal to 9% by volume). In some embodiments, the remainder of the gas provided by the gas source 430 may be helium-4 or essentially helium-4 (or a mixture of helium isotopes). For example, the gas provided by the gas source 430 may comprise helium gas in an amount greater than or equal to 90% by volume and less than or equal to 95% by volume and hydrogen gas in an amount greater than or equal to 5% by volume and less than or equal to 10% by volume.

[0061] In some embodiments, the gas in the thimble tube 115 may be pressurized above atmospheric pressure. For instance, the gas within the gas source 430 may be pressurized and / or one or more delivery mechanisms that transport the gas from the gas source into the thimble tube 115 may increase the pressure of the gas so that the gas inAttorney Docket No.: 226194-700620 / PCTthe thimble tube is above atmospheric pressure. In some embodiments, the pressure of the gas inside thimble tube 115 (whether as provided by the gas source, or increased in pressure through other means) may be greater than or equal to 1 atm, 1.5 atm, 2 atm, 2.5 atm, 3 atm, 3.5 atm, 4 atm, 4.5 atm, 5 atm, 5.5 atm, 6 atm, 6.5 atm, 7 atm, 7.5 atm, or 8 atm. In some embodiments, the pressure of the gas inside thimble tube 115 may be less than or equal to 8.5 atm, 8 atm, 7.5 atm, 7 atm, 6.5 atm, 6 atm, 5.5 atm, 5 atm, 4.5 atm, 4 atm, 3.5 atm, 3 atm, 2.5 atm, 2 atm, or 1.5 atm. Any suitable combinations of the abovereferenced ranges are also possible (e.g., the pressure of the gas inside thimble tube 115 is greater than or equal to 2 atm and less than or equal to 4 atm).

[0062] In some embodiments, the partial pressure of the helium gas inside thimble tube 115 (whether as provided by the gas source, or pressure controlled through other means) may be greater than or equal to 0.7 atm, 0.75 atm, 0.8 atm, 0.85 atm, 0.9 atm, 0.95 atm, 1 atm, 2 atm, 3 atm or 4 atm. In some embodiments, the pressure of the gas inside thimble tube 115 may be less than or equal to 5 atm, 4 atm, 3 atm, 2 atm, 1 atm, 0.95 atm, 0.9 atm, 0.85 atm, 0.8 atm, or 0.75 atm. Any suitable combinations of the above-referenced ranges are also possible (e.g., the partial pressure of the helium gas inside thimble tube 115 is greater than or equal to 0.8 atm and less than or equal to 0.95 atm).

[0063] Without wishing to be bound by theory, an increase in gas pressure may improve heat transfer between the capsule 105 and the gas in the thimble tube 115, and / or between the gas in the thimble tube 115 and the walls of the thimble tube due to the Knudsen effect. An increase in gas pressure may generally increase both the number of gas particle collisions and shorten the mean free path of the gas particles, which may not result in much (if any) increase in thermal transfer from the capsule to the gas to the thimble tube walls. However, in areas where the capsule is close to the wall of the thimble tube, the Knudsen effect may result in there being more gas particle collisions with the capsule or thimble tube wall compared with the amount of collisions between gas particles. For instance, areas where the capsule is close to the wall of the thimble tube may be particularly effective at transferring heat from the capsule to the thimble tube via the gas with increased gas pressure, even if the capsule does not touch the wall of the thimble tube. One example is the approach shown in FIG. 2 in which capsules areAttorney Docket No.: 226194-700620 / PCToriented in different directions so that some regions of a capsule may come closer to the thimble tube wall.

[0064] Any of the above-described techniques may be combined to increase heat dissipation from a capsule yet further. For example, a plurality of capsules may each comprise a thermal transport material as shown in FIG. 3 and may be coupled together in a chain that is configured to produce contact between one or more of the capsules and the interior of a guide tube when inserted into a reactor. Additionally, the guide tube into which the capsules are inserted may be backfilled with a gas, such as helium-4 gas, as shown in FIG. 4 and described above.

[0065] FIG. 5 is a flowchart of a method of transmuting one or more isotopes while dissipating heat from a capsule placed within a nuclear reactor, according to some embodiments. Method 500 may be performed using any suitable capsule described herein, including any of the embodiments of capsule 105 described herein, in addition to a suitable fission reactor or other environment comprising thermal neutrons.

[0066] Method 500 begins in act 502 in which a capsule comprising a target material is inserted into a fission reactor. A suitable process for inserting the capsule into a reactor is described above in relation to FIG. 1A, although any suitable process may be used so long as the capsule is placed in an area of neutron flux.

[0067] In act 504, the capsule is left in the reactor for a period of time during which a target isotope is produced in the target material as described above.

[0068] In some embodiments, the capsule may be left in the reactor for a time period greater than or equal to 5 hours, 10 hours, 20 hours, 2 days, 5 days, 10 days, 15 days, 20 days or 25 days. In some embodiments, the capsule may be left in the reactor for a time period that is less than or equal to 30 days, 25 days, 20 days, 15 days, 10 days, 5 days, 2 days, 20 hours, or 10 hours. Any suitable combinations of the abovereferenced ranges are also possible (e.g., the capsule may be left in the reactor for a time period of greater than or equal to 5 days and less than or equal to 10 days).

[0069] Optionally, in act 506 the capsule may be positioned within a guide tube of the reactor in contact with the guide tube. As described above, one way that this may beAttorney Docket No.: 226194-700620 / PCTachieved is to couple multiple capsules together in a series such the capsules are not oriented in the same direction, although other approaches may also be envisioned.

[0070] Optionally, in act 508 the guide tube is backfilled with a gas. Any approach described above, including those described in relation to FIG. 4, may be used. For example, act 508 may comprise evacuating the guide tube and backfilling the guide tube with a gas, such as helium -4 gas or a mixture of helium and hydrogen gas.

[0071] In act 510, the capsule is removed from the reactor and the target material is extracted from the capsule. In act 512, the target material is ‘milked’ for a desired isotope or isotopes, which is a process of chemically separating one element from other elements within the target material.

[0072] Optionally, a waiting period may be performed in act 508 between acts 506 and 510 so that some undesirable isotopes produced in the target material in act 504 have a chance to decay a suitable amount before milking starts. Since isotopes of the same element cannot be distinguished chemically, it may be advantageous to wait for several hours (e.g., seven or more hours) so that the vast majority of one isotope produced in the target material decays into another isotope. An initial actinium milking of the element can then be performed, which yields both isotopes, and the products discarded (or used for some other application), ensuring that subsequent milking of that element produces a pure, or highly pure sample with respect to the desired isotope.

[0073] After act 512 has been performed, if desired, the target material can be used in another iteration of method 500 by encapsulating it in a capsule (either the same or different capsule) and returning to act 502.

[0074] Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. For instance, aspects of the techniques described herein may be combined in any of the following ways:

[0075] Example 1. A capsule configured to be inserted into a nuclear reactor, the capsule comprising: a housing; a target material arranged within the housing; and a thermal transport material arranged within the housing and arranged at least partially between the target material and the housing.Attorney Docket No.: 226194-700620 / PCT

[0076] Example 2. The capsule of example 1, wherein the thermal transport material is a powder.

[0077] Example 3. The capsule of example 2, wherein the thermal transport material comprises diamond powder and / or aluminum powder.

[0078] Example 4. The capsule of example 1, wherein the thermal transport material is a solid having a higher coefficient of thermal expansion than the housing.

[0079] Example 5. The capsule of example 4, wherein the thermal transport material is solid diamond or aluminum.

[0080] Example 6. The capsule of example 1, wherein the target material and the thermal transport material are hermetically sealed within the capsule.

[0081] Example 7. The capsule of example 1, wherein the housing is a metal cylinder.

[0082] Example 8. The capsule of example 1, wherein the target material is encapsulated within a glass vessel.

[0083] Example 9. The capsule of example 1, wherein the target material comprises a radium compound at least partially enriched with radium-226.

[0084] Example 10. A method comprising: inserting a capsule into a thimble tube of a nuclear reactor, the capsule comprising a target material arranged within a housing; leaving the capsule in the thimble tube of the nuclear reactor for a first time period during which the housing of the capsule contacts the thimble tube and at least some of a first isotope within the target material is transmuted into a second isotope; and removing the capsule from the nuclear reactor.

[0085] Example 11. The method of example 10, further comprising pumping helium gas into the thimble tube.

[0086] Example 12. The method of example 11, comprising: operating at least one vacuum pump to evacuate the thimble tube; and backfilling the thimble tube with helium.

[0087] Example 13. The method of example 10, wherein the first time period is at least 5 days.Attorney Docket No.: 226194-700620 / PCT

[0088] Example 14. The method of example 10, further comprising milking the target material for the second isotope.

[0089] Example 15. The method of example 10, wherein the capsule is coupled to a cable, and wherein inserting the capsule into the nuclear reactor comprises operating a drive unit to feed the capsule and at least part of the cable into the thimble tube.

[0090] Example 16. The method of example 10, wherein the capsule further comprises a thermal transport material arranged within the housing and arranged at least partially between the target material and the housing.

[0091] Example 17. The method of example 16, wherein the thermal transport material is a solid having a higher coefficient of thermal expansion than the housing.

[0092] Example 18. The method of example 10, wherein the capsule is a metal cylinder.

[0093] Example 19. The method of example 10, wherein the target material comprises a radium compound at least partially enriched with radium-226.

[0094] Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Further, though advantages of the present invention are indicated, it should be appreciated that not every embodiment of the technology described herein will include every described advantage. Some embodiments may not implement any features described as advantageous herein and in some instances one or more of the described features may be implemented to achieve further embodiments. Accordingly, the foregoing description and drawings are by way of example only.

[0095] Various aspects of the present invention may be used alone, in combination, or in a variety of arrangements not specifically described in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.Attorney Docket No.: 226194-700620 / PCT

[0096] Also, the invention may be embodied as a method, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0097] Further, some actions are described as taken by a “user.” It should be appreciated that a “user” need not be a single individual, and that in some embodiments, actions attributable to a “user” may be performed by a team of individuals and / or an individual in combination with computer-assisted tools or other mechanisms.

[0098] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0099] The terms “approximately” and “about” may be used to mean within ±20% of a target value in some embodiments, within ±10% of a target value in some embodiments, within ±5% of a target value in some embodiments, and yet within ±2% of a target value in some embodiments. The terms “approximately” and “about” may include the target value. The term “substantially equal” may be used to refer to values that are within ±20% of one another in some embodiments, within ±10% of one another in some embodiments, within ±5% of one another in some embodiments, and yet within ±2% of one another in some embodiments.

[0100] The term “substantially” may be used to refer to values that are within ±20% of a comparative measure in some embodiments, within ±10% in some embodiments, within ±5% in some embodiments, and yet within ±2% in some embodiments. For example, a first direction that is “substantially” perpendicular to a second direction may refer to a first direction that is within ±20% of making a 90° angle with the second direction in some embodiments, within ±10% of making a 90° angle with the second direction in some embodiments, within ±5% of making a 90° angle withAttorney Docket No.: 226194-700620 / PCTthe second direction in some embodiments, and yet within ±2% of making a 90° angle with the second direction in some embodiments.

[0101] Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

[0102] What is claimed is:

Claims

Attorney Docket No.: 226194-700620 / PCTCLAIMS1. A capsule configured to be inserted into a nuclear reactor, the capsule comprising:a housing;a target material arranged within the housing; anda thermal transport material arranged within the housing and arranged at least partially between the target material and the housing.

2. The capsule of claim 1, wherein the thermal transport material is a powder.

3. The capsule of claim 2, wherein the thermal transport material comprises diamond powder and / or aluminum powder.

4. The capsule of claim 1, wherein the thermal transport material is a solid having a higher coefficient of thermal expansion than the housing.

5. The capsule of claim 4, wherein the thermal transport material is solid diamond or aluminum.

6. The capsule of claim 1, wherein the target material and the thermal transport material are hermetically sealed within the capsule.

7. The capsule of claim 1, wherein the housing is a metal cylinder.

8. The capsule of claim 1, wherein the target material is encapsulated within a glass vessel.

9. The capsule of claim 1, wherein the target material comprises a radium compound at least partially enriched with radium-226.Attorney Docket No.: 226194-700620 / PCT10. A method comprising:inserting a capsule into a thimble tube of a nuclear reactor, the capsule comprising a target material arranged within a housing;leaving the capsule in the thimble tube of the nuclear reactor for a first time period during which the housing of the capsule contacts the thimble tube and at least some of a first isotope within the target material is transmuted into a second isotope; and removing the capsule from the nuclear reactor.

11. The method of claim 10, further comprising pumping helium gas into the thimble tube.

12. The method of claim 11, comprising:operating at least one vacuum pump to evacuate the thimble tube; and backfilling the thimble tube with helium.

13. The method of claim 10, wherein the first time period is at least 5 days.

14. The method of claim 10, further comprising milking the target material for the second isotope.

15. The method of claim 10, wherein the capsule is coupled to a cable, and wherein inserting the capsule into the nuclear reactor comprises operating a drive unit to feed the capsule and at least part of the cable into the thimble tube.

16. The method of claim 10, wherein the capsule further comprises a thermal transport material arranged within the housing and arranged at least partially between the target material and the housing.

17. The method of claim 16, wherein the thermal transport material is a solid having a higher coefficient of thermal expansion than the housing.

18. The method of claim 10, wherein the capsule is a metal cylinder.Attorney Docket No.: 226194-700620 / PCT19. The method of claim 10, wherein the target material comprises a radium compound at least partially enriched with radium-226.

20. A method comprising:inserting a capsule into a thimble tube of a nuclear reactor, the capsule comprising a target material arranged within a housing;transferring a mixture of helium and hydrogen gas into the thimble tube; leaving the capsule in the thimble tube of the nuclear reactor for a first time period during which at least some of a first isotope within the target material is transmuted into a second isotope; andremoving the capsule from the nuclear reactor.

21. The method of claim 20, wherein the mixture of helium and hydrogen gas comprises greater than or equal to 4% hydrogen by volume and less than or equal to 8% hydrogen by volume.

22. The method of claim 21, wherein the mixture of helium and hydrogen gas comprises greater than or equal to 90% helium -4 by volume.

23. The method of claim 20, wherein the mixture of helium and hydrogen gas comprises greater than or equal to 1% hydrogen by volume and less than or equal to 8% hydrogen by volume.

24. The method of claim 23, wherein the mixture of helium and hydrogen gas comprises greater than or equal to 2% hydrogen by volume and less than or equal to 6% hydrogen by volume.

25. The method of claim 24, wherein the mixture of helium and hydrogen gas comprises greater than or equal to 3% hydrogen by volume and less than or equal to 5% hydrogen by volume.

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