System, method and apparatus for medical isotope production in an on-line nuclear reactor

Abstract

According to an aspect, there is provided a medical isotope element for producing medical isotopes during fuel burnup in a nuclear reactor. The medical isotope element includes at least one isotope target precursor, wherein the isotope target precursor converts to a medical isotope when exposed to radiation. In some embodiments, the medical isotope element is part of a fuel bundle. In some embodiments, the element is part of an assembly free of fissile material. According to an aspect, there is provided a method of producing medical isotopes during fuel burnup in a heavy water nuclear reactor. The method includes providing a fuel bundle or the assembly free of fissile material in the heavy water nuclear reactor, irradiating the fuel bundle or the assembly, removing the fuel bundle or the assembly from the heavy water reactor, and harvesting the medical isotope from the fuel bundle or the assembly.

Description

SYSTEM, METHOD AND APPARATUS FOR MEDICAL ISOTOPE PRODUCTION IN AN ON-LINE NUCLEAR REACTORCROSS-REFERENCE

[0001] This application claims priority from US Provisional Application No. 63 / 729033, entitled “SYSTEM AND METHOD FOR MULTIPLE MEDICAL ISOTOPE PRODUCTION IN HEAVY WATER REACTOR”, filed on December 6, 2024 and US Provisional Patent Application No. 63 / 733340, entitled “SYSTEM, METHOD AND APPARATUS FOR MEDICAL ISOTOPE PRODUCTION IN AN ON-LINE CANDU REACTOR”, filed on December 12, 2024, the contents of each of which are incorporated herein by reference.FIELD

[0002] Embodiments of the present disclosure generally relate to the field of medical isotopes, and more specifically to devices, systems, and methods for producing medical isotopes in on-line nuclear reactors.BACKGROUND

[0003] Medical isotopes (e.g., radioisotopes for medical use) have a variety of uses in a medical context. These can include diagnosis, treatment, sterilization, etc. For example, lodine-131 or lodine-123 tends to accumulate within the thyroid and the y-emission from those elements can then be used to image the thyroid for diagnostic purposes. As another example, Strontium-90 can be used to treat some cancers (such as bone cancer). Finally, the radioisotopes, such as Cobalt- 60, can be used to sterilize medical equipment by exposing the medical equipment to the y- emission.

[0004] That being said, the production of medical isotopes can present challenges. In the case of radioisotopes used for medical purposes the problem may further be compounded because radioisotopes will decay with time according to their half-life. Accordingly, it can be challenging not only to produce these medical isotopes in sufficient quantity, but to do so in a manner that can consistently provide timely medical isotopes based on medical demand.

[0005] Furthermore, the demand for medical isotopes is growing; however, production of medical isotopes has been limited, and a number of medical isotope production facilities arescheduled to reach end-of-life within the next decade. Production of medical isotopes in heavy water reactors, such as CAN DU type reactors, has been challenging because introduction of medical isotope(s) and their precursor(s) into the nuclear reactor has caused operational impacts due as the medical isotope(s) and their precursor(s) acting as neutron poisons forming pockets of reduced neutron activity within the reactor. Other attempts to produce medical isotopes in heavy water nuclear reactors on a small scale have been made by inserting medical isotope precursor into the reactor through an adjuster or dedicated view port of a CAN DU reactor moderator region. These systems are used to harvest the isotopes depending on the half-life of the medical isotope, for example, after few days for an isotope such as Molybdenum-99, or Lutecium-177, which may be operationally burdensome. Improvements to allow production of medical isotopes while minimizing negative the impacts on the operation of the nuclear reactor are desired.SUMMARY

[0006] Described herein are systems and methods which may enable mass scale production of medical isotopes using a CANDU environment with low impact on the core.

[0007] Nuclear reactors present an environment suitable to potentially produce medical isotopes (e.g., because of the neutron flux within the reactor). In particular, CANDU-type nuclear reactors which enable on-line refueling, may present a particularly advantageous environment in which to produce and extract medical isotopes on a somewhat consistent basis. For example, medical isotopes can be generated in one or more of the fuel bundles of the nuclear reactor and when the fuel bundle has been burnt up, then it can be removed in normal course and any medical isotopes produced therein can be harvested.

[0008] Producing medical isotopes in a plurality of the fuel bundles can provide a source of medical isotopes that replenishes on a relatively consistent basis (e.g., whenever a fuel bundle is switched out). Furthermore, with the strategies described herein, the isotope target precursor (which will become the medical isotope when irradiated) may not substantially perturb the power generation and control of the nuclear reactor. Accordingly, the nuclear reactor can still output the same level of power in addition to the new benefit of generating medical isotopes.

[0009] According to an aspect, there is provided an element for producing medical isotopes during fuel burnup in a nuclear reactor (also referred to herein as a “medical isotope element”). The medical isotope element includes at least one isotope target precursor, wherein the isotopetarget precursor converts to a medical isotope when exposed to radiation. In some embodiments, the medical isotope element is part of a fuel bundle. In some embodiments, the element is part of an assembly free of fissile material.

[0010] In some embodiments, the radiation includes neutron radiation.

[0011] In some embodiments, the radiation includes alpha, beta, and / or gamma radiation.

[0012] In some embodiments, the nuclear reactor is a CANDU-type nuclear reactor.

[0013] In some embodiments, the medical isotope includes a radioactive medical isotope.

[0014] In some embodiments, the medical isotope comprises at least one of Bismuth-213, Caesium-131 , Caesium-137, Chromium-51 , Cobalt-60, Dysprosium-165, Erbium-169, Holmium- 166, lodine-125, lodine-131 , lridium-192, Iron-59, Lead-212, Lutetium-177, Molybdenum-99, Palladium-103, Phosphorus-32, Potassium-42, Radium-223, Rhenium-186, Rhenium-188, Samarium-153, Scandium-47, Selenium-75, Sodium-24, Strontium-89, Technetium-99m, Thorium-227, Xenon-133, Ytterbium-169, Ytterbium-177, progenitor of Lu-177, Yttrium-90, and Hydrogen-3 (Tritium).

[0015] In some embodiments, the medical isotope exhibits a plateau in its mass build-up after an initial mass production period during irradiation.

[0016] In some embodiments, the isotope target precursor and the medical isotope are low neutron absorbing materials.

[0017] In some embodiments, the isotope target precursor or the medical isotope is a high neutron absorbing material. The high neutron absorbing material is provided in a smaller volume than a comparable low neutron absorbing material to reduce the impact on the nuclear reactor.

[0018] According to an aspect, there is provided a fuel bundle for producing medical isotopes during fuel burnup in a nuclear reactor, the fuel bundle including a plurality of elements wherein at least one element is the medical isotope element described above. The at least one medical isotope element is positioned in an inner or center fuel element position.

[0019] In some embodiments, the at least one medical isotope element is positioned at the center fuel element position.

[0020] In some embodiments, the fuel bundle is a 37- or 43-element bundle.

[0021] In some embodiments, the fuel bundle is a specifically modified bundle.

[0022] In some embodiments, a concentration of the isotope target precursor is provided in the at least one medical isotope element to cause a power loss below a threshold compared to a fuel bundle with a reference fuel element.

[0023] In some embodiments, the threshold is about 1.7%.

[0024] In some embodiments, the reference element is an element comprising natural uranium.

[0025] In some embodiments, at least a second element of the plurality of fuel elements compensates for the power loss.

[0026] According to an aspect, there is provided a process to produce medical isotopes during fuel burnup in a nuclear reactor. The process includes providing a medical isotope element or a fuel bundle described above in the nuclear reactor, burning the medical isotope element or the fuel bundle up in the nuclear reactor, removing the medical isotope element or the fuel bundle from the reactor after burnup, and harvesting the medical isotopes from the medical isotope element or the fuel bundle.

[0027] In some embodiments, the medical isotope element or the fuel bundle is removed while the nuclear reactor is online.

[0028] In some embodiments, most or all fuel bundles in the nuclear reactor comprises the fuel bundle described above.

[0029] In one aspect, the disclosure describes method of medical radioisotope production in a heavy water nuclear reactor, the method comprising: providing a plurality of fuel bundles each comprising a plurality of elements, wherein a first element of the plurality of elements of each of the plurality of fuel bundles comprises at least one isotope target precursor configured to be converted into a medical radioisotope, and the remaining elements of the plurality of elements comprise fissile material, wherein an amount of the at least one isotope target precursor and fissile material in each of the plurality of fuel bundles is selected to provide a desired burnup rate about equal to a reference fuel; inserting the plurality of fuel bundles into at least one fuel channel assembly of the heavy water nuclear reactor; irradiating the plurality of fuel bundles to convert theat least one isotope target precursor into a medical radioisotope; and removing the plurality of fuel bundles from the at least one fuel channel assembly of the heavy water nuclear reactor.

[0030] Embodiments may include combinations of the above features.

[0031] In another aspect, the disclosure describes a system for medical radioisotope production in a heavy water nuclear reactor, the system comprising: a heavy water nuclear reactor comprising a plurality of fuel channel assemblies; a plurality of fuel bundles each comprising a plurality of elements, wherein a first element of the plurality of elements of each of the plurality of fuel bundles comprises at least one isotope target precursor configured to be converted into a medical radioisotope, and the remaining elements of the plurality of elements comprise fissile material, wherein an amount of the at least one isotope target precursor and fissile material in each of the plurality of fuel bundles is selected to provide a desired burnup rate about equal to a reference fuel; at least one fuelling machine configured to insert the plurality of fuel bundles into at least one of the plurality of fuel channel assemblies in a first mode of operation and receive the plurality of fuel bundles once spent in a second mode of operation.

[0032] Embodiments may include combinations of the above features.

[0033] According to an aspect, there is provided a fuel bundle for producing medical isotopes during fuel burnup in a nuclear reactor. The fuel bundle includes a medical isotope element comprising at least one isotope target precursor configured to convert into at least one medical isotope when exposed to radiation and a plurality of fuel elements comprising fissile material. An amount of the at least one isotope target precursor and fissile material in each of the plurality of fuel bundles is selected to provide a desired burnup rate about equivalent to a reference fuel.

[0034] In some embodiments, the medical isotope element is positioned centrally within the bundle, preferably the medical isotope element is positioned at a center of the fuel bundle.

[0035] In some embodiments, a rate of increase in the mass of the at least one medical isotope is configured to plateau after an initial mass production period during irradiation.

[0036] In some embodiments, the medical isotope element having a composition of the at least one isotope in a range of up to 70%. In some embodiments, the medical isotope element having a composition of the at least one isotope in a range of 1-70%.

[0037] In some embodiments, the fuel bundle is a 37- or 43-element bundle.

[0038] In some embodiments, the fuel bundle is a specifically modified bundle.

[0039] In some embodiments, a concentration of the isotope target precursor is provided in the medical isotope element to cause a power loss below a threshold compared to a fuel bundle with the reference fuel.

[0040] In some embodiments, the threshold is about 1.3-2%, preferably the threshold is about 1.7%.

[0041] In some embodiments, the plurality of fuel elements comprises an amount of fissile material to compensate for the power loss.

[0042] In some embodiments, the reference fuel is natural uranium or slightly enriched uranium having a 0.9-2 wt% LI235.

[0043] According to an aspect, there is provided an assembly comprising an element for producing medical isotopes during fuel burnup in a heavy water nuclear reactor. The element includes at least one isotope target precursor for converting the at least one isotope target precursor to a medical isotope when exposed to radiation. A concentration of the isotope target precursor is provided in the element. The assembly is free of fissile fuel material.

[0044] In some embodiments, a rate of increase in the mass of the medical isotope is configured to plateau after an initial mass production period during irradiation.

[0045] In some embodiments, the radiation comprises neutron, alpha, beta, and / or gamma radiation.

[0046] In some embodiments, the nuclear reactor is a CAN Dll-type nuclear reactor.

[0047] In some embodiments, the medical isotope comprises a radioactive medical isotope.

[0048] In some embodiments, the medical isotope includes at least one of Bismuth-213, Caesium-131 , Caesium-137, Chromium-51 , Cobalt-60, Dysprosium-165, Erbium-169, Holmium- 166, lodine-125, lodine-131 , lridium-192, Iron-59, Lead-212, Lutetium-177, Molybdenum-99, Palladium-103, Phosphorus-32, Potassium-42, Radium-223, Rhenium-186, Rhenium-188, Samarium-153, Scandium-47, Selenium-75, Sodium-24, Strontium-89, Technetium-99m, Thorium-227, Xenon-133, Ytterbium-169, Ytterbium-177, progenitor of Lu-177, Yttrium-90, and Hydrogen-3 (Tritium).

[0049] In some embodiments, the isotope target precursor or the medical isotope is a high neutron absorbing material, wherein the high neutron absorbing material is provided in a smaller volume than a comparable low neutron absorbing material to reduce the impact on the nuclear reactor.

[0050] In some embodiments, the at least one isotope target precursor comprises a plurality of isotope target precursors.

[0051] In some embodiments, the assembly comprises support members for positioning the element in a fuel channel of the nuclear reactor.

[0052] According to an aspect, there is provided a system for medical isotope production in a heavy water nuclear reactor. The system includes the heavy water nuclear reactor comprising a plurality of fuel channel assemblies, a plurality of medical isotope assemblies each comprising a medical isotope precursor configured to convert into at least one medical isotope when exposed to radiation, and at least one fuelling machine configured to insert the plurality of medical isotope assemblies into at least one of the plurality of fuel channel assemblies in a first mode of operation and remove the plurality of medical isotope assemblies from the plurality of fuel channel assemblies once spent in a second mode of operation. The at least one fuelling machine is configured to position the plurality of medical isotope assemblies in at least one of the plurality of fuel channel assemblies in the first mode of operation. After a rate of increase in the mass of the at least one medical isotope of at least one of the plurality of medical isotope assemblies plateaus during irradiation forming at least one mature medical isotope assembly, the second mode of operation begins and the at least one mature medical isotope assembly is removed from the at least one fuel channel of the heavy water nuclear reactor.

[0053] In some embodiments, the at least one fuelling machine is configured to insert the plurality of assemblies into at least two or more of the plurality of fuel channel assemblies for concurrent production of medical isotopes.

[0054] In some embodiments, the plurality of medical isotope assemblies comprise at least one of the fuel bundle as described above and the assembly as described above.

[0055] In some embodiments, the plurality of medical isotope assemblies comprise at least one of the fuel bundle as described above, and each of the plurality of fuel bundles has about the same k-infinity to burnup ratio.

[0056] In some embodiments, a mass of the isotope target precursor is selected to provide about equal reactivity decay for each of the plurality of fuel bundles.

[0057] In some embodiments, the at least one fuelling machine is configured to remove the plurality of fuel bundles at a desired exit burnup of the fissile material after the at least one mature medical isotope assembly is formed.

[0058] In some embodiments, the at least one fuelling machine inserts the plurality of medical isotope assemblies in at least one of: one of the plurality of fuel channel assemblies; greater than 25% of the plurality of fuel channel assemblies; greater than 50% of the plurality of fuel channel assemblies; greater than 75% of the plurality of fuel channel assemblies; or all of the plurality of fuel channel assemblies, for concurrent reaction within the heavy water nuclear reactor.

[0059] In some embodiments, the plurality of medical isotope assemblies includes a first group of medical isotope assemblies each having a first isotope target precursor and a second group of medical isotope assemblies having a second isotope precursor. The first group of medical isotope assemblies are inserted into the plurality of fuel channel assemblies to define a first zone defined by a first distance range from a center of the heavy water nuclear reactor. The second group of medical isotope assemblies are inserted into the plurality of fuel channel assemblies to define a second zone defined by a second distance range from a center of the heavy water nuclear reactor. The first distance range is non-overlapping with the second distance range.

[0060] In some embodiments, a neutron cross section of a first medical radioisotope produced from the first isotope target precursor in the first zone is greater than the neutron cross section of a second medical radioisotope produced from the second isotope target precursor in the second zone.

[0061] According to an aspect, there is provided a method of producing medical isotopes during fuel burnup in a heavy water nuclear reactor. The method includes providing the fuel bundle as described above or the assembly as described above in the heavy water nuclear reactor, irradiating the fuel bundle or the assembly in the heavy water nuclear reactor, removing the fuel bundle or the assembly from the heavy water reactor, and harvesting the at least one medical isotope from the fuel bundle or the assembly.

[0062] In some embodiments, the method includes providing a plurality of the fuel bundles as described above. Each of the plurality of fuel bundles has about the same k-infinity to burnup ratio.

[0063] In some embodiments, a mass of the isotope target precursor is selected to provide about equal reactivity decay for each of the plurality of fuel bundles.

[0064] In some embodiments, the fuel bundle or the assembly is removed from the heavy water nuclear reactor at a desired exit burnup of the fissile material after the at least one mature medical isotope assembly is formed.

[0065] In some embodiments, the fuel bundle or the assembly is removed while the nuclear reactor is online.

[0066] Many further features and combinations thereof concerning embodiments described herein will appear to those skilled in the art following a reading of the instant disclosure.DESCRIPTION OF THE FIGURES

[0067] In the figures,

[0068] FIG. 1 is a perspective view of a CANDUTM-type reactor, according to some embodiments.

[0069] FIG. 2 is a cutaway view of a CANDU™-type nuclear reactor fuel channel assembly, according to some embodiments.

[0070] FIG. 3 is an image of a CANDUTM-type fuel bundle, according to some embodiments.

[0071] FIG. 4 illustrates an embodiment of the annulus spacer installed within the annulus space between the CT and the PT, according to some embodiments.

[0072] FIG. 5 is a graph showing Molybdenum-99 build-up in a CANDUTM-type fuel bundle, according to some embodiments.

[0073] FIG. 6A is a cross-sectional view of a CANDU™-type fuel bundle with a medical isotope element, according to some embodiments.

[0074] FIG. 6B is a cross-sectional view of an assembly with a medical isotope element, according to some embodiments.

[0075] FIG. 7 illustrates a schematic process diagram for a method of producing medical isotopes, according to some embodiments.

[0076] FIG. 8 is a schematic face view of a CANDU™-type reactor core showing a channel and reflector region, according to some embodiments.

[0077] FIG. 9A is a schematic view of an example heavy water nuclear reactor and fueling machines, according to some embodiments.

[0078] FIG. 9B is a schematic view of a cross-section of a heavy water nuclear reactor divided into zones for production of distinct medical isotopes, according to some embodiments.

[0079] FIG. 10 is graphical plot of k-infinity and bundle burnup for example fuel bundles according to this disclosure comprising isotope target precursors of Lu-177, Mo-99, Sr-89, Y-90, 1131 , and a reference natural uranium fuel bundle, according to some embodiments.

[0080] FIG. 11 is a graphical plot of a neutron cross-section and incident neutron energy for Lu-177, 1-131 , Mo-99, Y-90, and Sr-89, according to some embodiments.

[0081] FIG. 12 is a schematic diagram illustrating a method for medical radioisotope production in a heavy water nuclear reactor, according to some embodiments.

[0082] FIG. 13 is a schematic diagram illustrating a method for medical radioisotope production in a heavy water nuclear reactor, according to some embodiments.DETAILED DESCRIPTION

[0083] This disclosure is directed to medical isotope production using a heavy water nuclear reactor where medical isotopes may be produced in multiple fuel bundles concurrently in the nuclear reactor. The medical isotopes and their precursors may be physically completely different from each other in terms of half-life, absorption property, production characteristics, decay chains, and their application purposes. Typically, medical isotopes with different properties are difficult to produce at the same time without causing operational issues to the reactor core. The issues generally relate to the control of reactor power and neutron flux during the nuclear reactor operation, locally and globally in the core, which eventually disable stable control of reactorregulating system that is known as the Reactor Regulating System (RRS). However, according to the systems and method according to this disclosure, multiple isotope production may occur without operational issues to the heavy water nuclear reactor by controlling the physical property of each medical isotope target precursor and fissile material in nuclear fuel bundles. For example, the neutronic property of each fuel bundle, e.g. a CANDll fuel bundle, comprising an isotope target precursor, may be selected to be similar to a reference fuel bundle (for example, natural uranium 37-element bundles (37M)). Because each fuel bundle comprising a medical isotope precursor has about the same burnup rate / reactivity decay, each fuel channel of the heavy water nuclear reactor may contain different types of isotope target precursors in fuel bundles which have similar reactivity and performance. Similarly, each fuel channel assembly may also contain fuel bundles comprising different isotope target precursors. The fuel bundles may have at least one isotope target precursor in a core, e.g. center, of each bundle and may provide stable reactivity since each bundle in each fuel channel may be adjusted to have the same behaviour as the reference fuel. The isotope target precursor and medical isotope behaviour in each fuel bundle may be almost the same as the reference fuel because the volume (or mass) of the isotope target precursor and fissile material is selected to achieve a similar pattern of reactivity decay as the reference fuel.

[0084] Before any embodiments are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The disclosure is capable of other embodiments and of being practiced or of being carried out in various ways.

[0085] DEFINITIONS

[0086] Although terms such as “maximize”, “minimize” and “optimize” may be used in the present disclosure, it should be understood that such terms may be used to refer to improvements, tuning and refinements which may not be strictly limited to maximal, minimal or optimal.

[0087] The term “connected” or "coupled to" may include both direct coupling (in which two elements that are coupled to each other and contact each other) and indirect coupling (in which at least one additional element is located between the two elements).

[0088] The term “substantially” as used herein may be applied to modify any quantitative representation which could permissibly vary without resulting in a change in the basic function to which it is related.

[0089] Terms such as "up to", "at least", "greater than", "less than", "more than", "or more", and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges. In the same manner, all ratios recited herein also include all subratios falling within the broader ratio.

[0090] The singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise. The term "and / or" means any one of the items, any combination of the items, or all of the items with which this term is associated.

[0091] The term "about" can refer to a variation of± 5%, ± 10%, ± 20%, or± 25% of the value specified. For example, "about 50" percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term "about" can include one or two integers greater than and / or less than a recited integer at each end of the range. Unless indicated otherwise herein, the term "about" is intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment.

[0092] GENERAL REACTOR DESIGN DETAILS

[0093] FIG. 1 is a perspective of a reactor core of a CANDU™-type reactor 6. The CAN DU reactor is a pressure-tube reactor using natural uranium as fuel and heavy water as both moderator and coolant. A cylindrical reactor vessel called the calandria vessel 10 can be positioned horizontally. Inside the calandria vessel 10, there can be a total of 380 (or 480) fuel channel assemblies 28 containing fuel and coolant at high pressure. Each fuel channel assembly 28 can contain twelve 49.53-centimeter-long fuel bundles 40 and provides coolant flow passage. The moderator can occupy the space between the coolant or fuel channels, and can be kept at near atmospheric pressure, and at a relatively low temperature. Reactivity devices, such as fourteen light water zone-control compartments, twenty-one adjuster rods, four mechanical control absorber rods, and twenty-eight shutoff rods can be inserted interstitially between fuel channels.

[0094] The core of calandria 10 may be characterized as fuel channel region and reflector region (see FIG. 8) inside calandria 10 where heavy water reflector surrounds the fuel channels.Inside the calandria vessel 10, a heavy water reflector can surround the fuel channel assemblies 28. Inside each fuel channel assemblies 28, about twelve fuel bundles 40 (see, for example, FIG. 3 for a bundle 40 made up of a plurality of elements 500) can be loaded and refuelled online. In case of CAN DU 6, about two fuel channel assemblies 28 (or sixteen bundles 40 based on eight bundle shift scheme) can be refuelled every day.

[0095] The reactor core is typically contained within a vault that is sealed with an air lock for radiation control and shielding. Although aspects are described with particular reference to the CANDUTM-type reactor 6 for convenience, the disclosure is not limited to CANDUTM-type reactors, and may be useful outside this particular field as well. A generally cylindrical vessel, known as the calandria vessel 10 of the CANDUTM-type reactor 6, contains a heavy-water moderator. The calandria vessel 10 has an annular shell 14 and a tube sheet 18 at a first end 22 and a second end 24. The tube sheets 18 include a plurality of apertures (referred to herein as “bores” 19) that each accept a fuel channel assembly 28. As shown in FIG. 1 , a number of fuel channel assemblies 28 pass through the tube sheets 18 of calandria vessel 10 from the first end 22 to the second end 24.

[0096] As in the illustrated embodiments of FIG. 1 and FIG. 2, in some embodiments the reactor core is provided with two walls at each end 22, 24 of the reactor core: an inner wall defined by the tube sheet 18 at each end 22, 24 of the reactor core, and an outer wall 64 (often referred to as a “end shield” and illustrated in FIG. 2) located a distance outboard from the tube sheet 18 at each end 22, 24 of the reactor core. A lattice tube 65 spans the distance between the tube sheet 18 and the end shield 64 at each pair of bores 19 (i.e. , in the tube sheet 18 and the end shield 64, respectively).

[0097] FIG. 2 is a cutaway view of one fuel channel assembly 28 of the reactor core illustrated in FIG. 1. As illustrated in FIG. 2, each fuel channel assembly 28 includes a calandria tube (“CT”) 32 surrounding other components of the fuel channel assembly 28. The CTs 32 each span the distance between the tube sheets 18. Also, the opposite ends of each CT 32 are received within and sealed to respective bores 19 in the tube sheets 18. In some embodiments, a rolled joint insert, for example calandria tube rolled joint insert 34, is used to secure the CT 32 to the tube sheet 18 within the bores 19. A pressure tube (“PT”) 36 forms an inner wall of the fuel channel assembly 28. The PT 36 provides a conduit for reactor coolant and fuel bundles or assemblies 40. The PT 36, for example, generally holds two or more fuel assemblies 40, and acts as a conduit for reactor coolant that passes through each fuel assembly 40. An annulus space 44 is definedby a gap between each PT 36 and its corresponding CT 32. The annulus space 44 is normally filled with a circulating gas, such as dry carbon dioxide, helium, nitrogen, air, or mixtures thereof. One or more annulus spacers 48 are disposed between the CT 32 and PT 36. The annulus spacers 48 maintain the gap between the PT 36 and the corresponding CT 32, while allowing passage of annulus gas through and around the annulus spacers 48.

[0098] FIG. 4 illustrates an embodiment of the annulus spacer 48 installed within the annulus space 44 between the CT 32 and the PT 36, according to some embodiments.

[0099] The annulus spacer 48 includes a garter spring 52 and a girdle wire 56. The exemplary garter spring 52 is formed from a length of coiled wire 61 . Two ends 74 and 78 of the coiled wire 61 are connected so that the garter spring 52 forms a toroid 72. The garter spring 52 can be dimensioned to fit tightly around the PT 36, and to be both resilient so that it may be expanded to a dimension greater than an outside diameter 76 of the PT 36 during installation, yet to fit tightly and securely once positioned. In the illustrated embodiment, the garter spring 52 is formed from a nickel-chromium based alloy such as INCONEL X-750. In other embodiments, the garter spring 52 may be formed of other alloys, including a zirconium-based alloy such as ZIRCALOY or a zirconium-niobium-copper alloy. In still other embodiments, the garter spring 52 may be formed of an alloy including, but not limited to, a combination of zirconium, niobium, and copper.

[0100] As also shown in FIG. 2, each end of each fuel channel assembly 28 is provided with an end fitting assembly 50 located outside of the corresponding tube sheet 18. Each end fitting assembly 50 includes an end fitting body 57 and an end fitting liner 58. At the terminal end of each end fitting assembly 50 is a closure plug 52. Each end fitting assembly 50 also includes a feeder assembly 54. The feeder assemblies 54 feed reactor coolant into or remove reactor coolant from the PTs 36 via feeder tubes 59 (FIG. 1). In particular, for a single fuel channel assembly 28, the feeder assembly 54 on one end of the fuel channel assembly 28 acts as an inlet feeder, and the feeder assembly 54 on the opposite end of the fuel channel assembly 28 acts as an outlet feeder. As shown in FIG. 2, the feeder assemblies 54 can be attached to the end fitting assemblies 50 using a coupling assembly 56 including a number of screws, washers, seals, and / or other types of connectors. The lattice tube 65 (described above) encases the connection between the end fitting assembly 50 and the PT 36 containing the fuel assemblies 40. Shielding ball bearings 66 and cooling water surround the exterior of the lattice tubes 65, which provides additional radiation shielding.

[0101] A positioning hardware assembly 60 and bellows 62 are also coupled to each end fitting assembly 50. The bellows 62 allows the fuel channel assemblies 28 to move axially - a capability that can be important where fuel channel assemblies 28 experience changes in length over time, which is common in many reactors. The positioning hardware assemblies 60 can be used to set an end of a fuel channel assembly 28 in either a locked configuration that fixes the axial position, or an unlocked configuration. The positioning hardware assemblies 60 are also coupled to the end shield 64. The illustrated positioning hardware assemblies 60 each include a rod having an end that is received in a bore of the respective end shield 64. In some embodiments, the rod end and the bore in the end shield 64 are threaded. Again, it should be understood that although a CANDUTM-type reactor is illustrated in FIG. 1 and FIG. 2, the invention may also apply to other types of reactors, including reactors having components that are similar to those illustrated in FIG. 1 and FIG. 2.

[0102] MEDICAL ISOTOPES

[0103] Medical isotopes can refer to isotopes used for medical purposes such as diagnostic tests, treatment, and sterilization (e.g., of equipment). Medical isotopes can refer to both radioactive and non-radioactive isotopes. Radioactive isotopes (i.e., radioisotopes) are isotopes which decay and release energy and / or matter in the form of radiation. The radiation emitted from these radioisotopes can be used in medicine for treatment, diagnosis, and sterilization. Nonradioactive isotopes (e.g., Deuterium or Carbon-13) can be used to impact the pharmacokinetics of drugs or used in testing.

[0104] The current medical isotope market size is large and may more than tripled within 10 years. Accordingly, methods to mass produce medical isotopes on a consistent basis may represent a key achievement in supporting this market growth and increased demand.

[0105] Nuclear reactors are already generating an environment that is suitable for the production of medical isotopes. Accordingly, retrofitting or otherwise adapting current nuclear techniques to accommodate medical isotope production may provide an additional source of medical isotopes without the need of establishing, building, or maintaining new nuclear facilities. Such techniques may be used to produce medical isotopes in mass production.

[0106] PRODUCING MEDICAL ISOTOPES IN A CANDU-TYPE REACTOR

[0107] Described herein are systems and methods to produce the medical isotopes while maintaining operational safety and control using the center element of CAN DU fuel bundle in a CANDU-type reactor (CANDU 6, Darlington, Bruce Power, EC6, AFCR, MONARK, etc.), which can consist of 37 elements (37-regular or 37-modified), 43 (CAN FLEX) elements, or other variant designs with different number of elements and with different level of enrichment.

[0108] The isotope target precursors (to produce the product medical isotopes) are generally neutron absorbers and some of them may be highly absorbing. Accordingly, when certain isotope target precursors are introduced in the channels, the reactor core power can be impacted. In some cases, this may cause core shutdown or disable the safe operation (especially during loading and unloading). Even when only a few channels have isotope target precursors therein introduced into all of the elements of the fuel bundle, there may still be a high impact on the core.

[0109] Accordingly, using just the center element the fuel bundle, for example in many or all of the fuel bundles in the nuclear reactor, may provide a viable way to produce medical isotopes while minimizing the perturbation in the local power. This strategy can allow full-core loading of bundles with medical isotopes in the bundle, which can enable mass production of a certain type of isotope. Furthermore, configuring the fuel bundles to tolerate the presence of the medical isotope once its mass has built-up from its generation can enable the medical isotopes to be harvested when the fuel channel is being refueled (rather than scheduling harvest based on the medical isotope production) following its normal schedule. Having each fuel bundle contain a certain type of medical isotope can provide a consistent source of the medical isotope as refueling is (usually) a daily occurrence.

[0110] FIG. 5 is a graph showing Molybdenum-99 build-up in a CANDUTM-type fuel bundle, according to some embodiments.

[0111] Most isotopes have a mass build-up life cycle curve as illustrated in FIG. 5. Accordingly, the isotope mass stays close to a constant after it reaches a certain plateau The plateau may represent the balance between the production reactions and the decay reactions. The amplitude of the plateau may be proportional to the flux level at the isotope location. This plateau enables the medical isotopes to be left in the reactor while the fuel bundle continues to burnup (e.g., delayed harvesting). This property can allow the medical isotopes to be harvested during regular refueling operations (rather than in a specific additional step that may interfere with reactor operation). The fuel can stay as long as it is needed to stabilize the core in a safe operation regionbecause there is limited mass loss after a certain point. Furthermore, in filling many or all of the fuel channels with fuel bundles that include an isotope target precursor that will become a medical isotope, the medical isotopes can be more consistently harvested to meet the demand and so the channels don’t need to be prematurely harvested. According to standard refueling procedures, in some current CAN DU 6 nuclear reactors, this means that about two channels can be harvested daily at maximum capacity which means that two channels worth of medical isotopes can reliably be harvested daily. In some embodiment, a plurality of fuel channels may be loaded with fuel bundles 40 or assemblies 41 , comprising at least one medical isotope precursor according to this disclosure (e.g., at least one medical isotope element 502 as described below), such that the fissile material of a least one fuel bundle is spent (or reached a desired burn-up rate for removal) at a desired schedule, e.g. daily, and the at least one fuel bundle 40 can be removed from the fuel channel(s). This may permit constant supply of one or more medical isotopes from the nuclear reactor on a predetermined desired schedule.

[0112] The systems and methods described herein provide a medical isotope element 502 that can produce medical isotopes during fuel burnup in a nuclear. The element 502 includes some isotope target precursor that, when irradiated in the nuclear reactor, converts (either directly or indirectly) into a medical isotope. In general, the production of isotopes can be more effective with thermal neutron radiation in CAN DU reactors.

[0113] The medical isotope produced from this process can potentially include any medical isotope. In particular, the medical isotope produced can be radioactive isotopes such as, for example, Bismuth-213, Caesium-131 , Caesium-137, Chromium-51 , Cobalt-60, Dysprosium-165, Erbium-169, Holmium-166, lodine-125, lodine-131 , lridium-192, Iron-59, Lead-212, Lutetium-177, Molybdenum-99, Palladium-103, Phosphorus-32, Potassium-42, Radium-223, Rhenium-186, Rhenium-188, Samarium-153, Scandium-47, Selenium-75, Sodium-24, Strontium-89, Technetium-99m, Thorium-227, Xenon-133, Ytterbium- 169, Ytterbium-177, progenitor of Lu-177, Yttrium-90, or Hydrogen-3 (Tritium).

[0114] Isotope target precursors can be selected that are low neutron absorbing materials to enable mass production, that is, to allow to load more medical isotope producing bundles up to the entire core. For example, Strontium-99 can be fully loaded into each bundle 40 without absorbing to many neutrons to negatively impact the nuclear reaction 6. Even in the case of high neutron absorbing materials (e.g., Cobalt-60), center elements with very low volumes can be used to make the modified fuel bundle have similar neutronic property to the reference fuel bundle.Such a method can be used to accommodate bundles with high neutron absorbing materials in as many bundles as possible while reducing the impact on core operation.

[0115] For example, the isotope target precursors can be selected and provided in a concentration in the element 502 such that the fuel bundle 40 containing the element 502 has similar neutronic and thermal-hydraulic properties as a reference fuel (e.g., a standard fuel bundle).

[0116] In some embodiments, the isotope target precursors and / or produced medical isotopes are non-fissile and can be parasitic neutron absorbers. This can contribute to reducing the coolant void reactivity and help mitigation of large loss of coolant accident power pulse.

[0117] Table 1 : Exemplary Center Element 500a Compositions of Medical Isotope Elements502. These compositions are for use with 37M Nil in CAN DU 6 Type Reactors.

[0118] Table 1 provides some exemplary compositions of isotope target precursors for conversion to medical isotopes, according to some embodiments. There may be range variation for each target oxide of up to a few percentage points. The compositions include one or more target isotope which may be converted to the medical isotope of interest. Each compound is the mixture of isotope target precursor and Zirconia (Zr2O3) (and glass in the case item 3). The Zirconia may have variation of its composition of up to a few tens of percentage points. Zirconia can be used as it absorbs few neutrons. Other materials can be used in place of Zirconia. Different concentrations may be used for different types of nuclear reactor 6 or for different operating conditions.

[0119] The element 502 may include the isotope target precursor. Different fuel bundles 40 may include different isotope target precursors. The isotope itself may be limited to a singleisotope target precursor to keep the manufacturing and processing (e.g., constructions / harvesting) relatively simple.

[0120] FIG. 6A is a cross-sectional view of a CANDUTM-type fuel bundle 40 with a medical isotope element 502, according to some embodiments.

[0121] The fuel bundle 40 can include a plurality of elements 500 inclusive of the center element 500a and the inner elements 500b. The fuel bundles 40 described herein can include a medical isotope element 502 that is an element 500 that includes the isotope target precursor and may not include fissile material. As illustrated, the medical isotope element 502 may be positioned at a center element position 500a and / or elsewhere within the plurality of elements 500. In the fuel bundle the elements 500 which are not medical isotope elements 502 may be fuel elements 504 (e.g., they may include fissile materials). The medical isotope element 502 may include support structure and cladding for the medical isotope element 502. The described medical isotope element 502 can be advantageously provided in the center of the fuel bundle 40 (e.g., at a center of the fuel bundle 40 when seen cross-sectionally (the appearance of the fuel bundle 40 internal structure as it would look if a cut were made through its middle, perpendicular to its longest axis), e.g., center element 500a position). In some embodiments, the medical isotope element 502 may be provided in the inner element 500b. The isotope target precursor provided in the center element 500a causes a small amount of power loss for the bundle (e.g., 1-2%, or 1 .7% in some embodiments) when compared to a standard fuel bundle 40 (one with a center element with the same composition as all the other fuel elements). The other elements 500 in the bundle (e.g., the fuel elements 504) can be configured to compensate for the power deficit by a slight increase of flux level, and thus no modification may be needed.

[0122] In a heavy water nuclear reactor 6, isotopes can either form spontaneously (naturally) through radioactive decay of a nucleus (i.e. , emission of energy in the form of alpha particles, beta particles, neutrons, and photons) or artificially by bombarding a stable nucleus with charged particles via accelerators or neutrons in a nuclear reactor. In some cases, a new isotope of the same element is produced. In other cases, an element is converted to another element in a process called "transmutation". The isotope target precursor is the element that is transformed into a desired medical isotope when exposed to radiation in the heavy water nuclear reactor 6.

[0123] The fuel bundle 40 described herein can be inserted into a nuclear reactor (e.g., a CAN Dll-type nuclear reactor 6) to burnup (that is to say to have the usable fissile material in thebundle substantially consumed during normal reactor operation). The fuel bundle 40 can then be removed from the reactor core and the generated medical isotopes can be harvested. The removal of the fuel bundle 40 can occur while the reactor is still online (as is standard in CANDU- type reactors 6). Many or all of the fuel bundles 40 in the reactor may include an isotope target precursor (e.g., a medical isotope element 502) to become a medical isotope in their center elements 500a which may provide a consistent source of medical isotopes without impairing reactor function. The fuel bundles 40 configured in this way may allow the medical isotopes to be a harvested during the scheduled refueling times following the normal fuel refueling schedule (rather than based on the production of the medical isotope reaction) without jeopardizing the operational core safety.

[0124] Producing medical isotopes in the CANDll environment can be completed with low impact on the core. Specifically, using the center element 500a of a fuel bundle 40 to produce isotopes may only produce a limited impact on the core as the center element power is about 1- 2%, or 1.7% in some example embodiments, of the total fuel element power and can be compensated by the other elements (e.g., fuel elements 504). The other elements 504 may have more power extracted therefrom such that the power from the fuel bundle 40 stays remains the same. The overall fuel burnup may be slightly reduced (e.g., by 2.7%). In some embodiments, the other elements 504 may have more fuel provided therein (e.g., slight enrichment). The systems and methods described herein may reduce the impact on the core (e.g., through reactivity perturbation) and may enable on-line refuelling schedule harvest. Doing so can enable the mass scale (e.g., full CANDll core) production of a medical isotope. Furthermore, this may be implemented in a manner which does not derate the power level.

[0125] In particular, center elements 500a of the CANDU-type fuel bundle 40 offer features that make them particularly well suited to medical isotope generation. The high neutron flux and soft spectrum of CANDU-type reactors 6 is a good fit to enhance the production of medical isotopes by its design. A soft spectrum means that there are more slow neutrons (lower energy) compared to the fast neutrons (higher energy). Such reactors 6 are referred to as thermal reactors. CANDU- type reactors 6 have soft spectra. The reaction rate is higher with slow neutrons. This means that more isotopes can be generated with slower neutrons in most cases. Furthermore, CANDU-type reactors 6 are re-fueled while online meaning that produced medical isotopes can be harvested without shutting the reactor 6 down. The impact of medical isotope production on the reactor 6 operation is within tolerance for power and flux variations.

[0126] The systems and methods described herein can minimize the impact to the core (especially during loading and unloading the fuel bundles 40) by only using center elements 500a (see, for example, FIG. 6A). The power portion of typical CANDll center fuel element 500a out of the entire fuel bundle 40 is about 1-2%, or 1.7% in some embodiments, of the total fuel elements 504. Accordingly, that corresponding amount of power deficit (1-2%) may happen with full core loading (i.e., all center elements 500a loaded with a single target element). The deficit power can be compensated from the remaining fuel elements, which means that the core does not need to be derated (unless for other reasons such as aging).

[0127] In some embodiments, there may be multiple medical isotope elements 502 that contain the isotope target precursor. In some embodiments, the multiple medical isotope elements 502 may include the center element position 500a and one or more of the inner element positions 500b. In some embodiment, the multiple medical isotope elements 502 may be distributed in a pattern around the fuel bundle 40 (e.g., to distribute their impact on the internal neutron flux of the bundle 40). In such embodiments, the core of the nuclear reactor 6 may be loaded with fewer fuel bundles 40 that contain isotope target precursors. For example, if the bundle 40 includes two medical isotope elements, then only half the fuel channel assemblies 28 may include such two medical isotope element bundles 40 and the other half may be conventional fuel bundles 40. If the bundle 40 includes three medical isotope elements, then only a third of the fuel channel assemblies 28 may include such three medical isotope element bundles 40 and the other two thirds may be conventional fuel bundles 40. This approach may be used to produce more medical isotopes with a single fuel bundle 40 (e.g., if there is a forecasting increase in demand), while still generally maintaining the same power output from the nuclear reactor 6.

[0128] The medical isotopes may be harvested by extracting the fuel bundle 40 from the reactor 6. The medical isotope element(s) 502 is removed. The cladding is then cut away to harvest the medical isotope.

[0129] According to an aspect, there is provided an element 502 for producing medical isotopes during fuel burnup in a nuclear reactor 6. The element 502 includes at least one isotope target precursor, wherein the isotope target precursor converts to a medical isotope when exposed to radiation.

[0130] In some embodiments, the radiation includes neutron radiation.

[0131] In some embodiments, the radiation includes alpha, beta, and / or gamma.

[0132] In some embodiments, the nuclear reactor 6 is a CANDU-type nuclear reactor.

[0133] In some embodiments, the medical isotope includes a radioactive medical isotope.

[0134] In some embodiments, the medical isotope comprises at least one of Bismuth-213, Caesium-131, Caesium-137, Chromium-51, Cobalt-60, Dysprosium-165, Erbium-169, Holmium- 166, lodine-125, lodine-131 , lridium-192, Iron-59, Lead-212, Lutetium-177, Molybdenum-99, Palladium-103, Phosphorus-32, Potassium-42, Radium-223, Rhenium-186, Rhenium-188, Samarium-153, Scandium-47, Selenium-75, Sodium-24, Strontium-89, Technetium-99m, Thorium-227, Xenon-133, Ytterbium-169, Ytterbium-177, progenitor of Lu-177, Yttrium-90, and Hydrogen-3 (Tritium).

[0135] In some embodiments, the isotope target precursor comprises a Target Compound Composition of Table 1.

[0136] In some embodiments, the medical isotope exhibits a plateau in its mass build-up after an initial mass production period during irradiation.

[0137] In some embodiments, the isotope target precursor and the medical isotope are low neutron absorbing materials.

[0138] In some embodiments, the isotope target precursor or the medical isotope is a high neutron absorbing material. The high neutron absorbing material is provided in a smaller volume than a comparable low neutron absorbing material to reduce the impact on the nuclear reactor.

[0139] According to an aspect, there is provided a fuel bundle 40 for producing medical isotopes during fuel burnup in a nuclear reactor 6, the fuel bundle 40 including a plurality of elements 500 wherein at least one element 502 is the medical isotope element 502 described above. The at least one element 502 is positioned in an inner 500b or center element position 500a.

[0140] In some embodiments, the at least one element 502 is positioned at the center element position 500a.

[0141] In some embodiments, the fuel bundle 40 is a 37- or 43-element bundle.

[0142] In some embodiments, the fuel bundle 40 is a specifically modified bundle.

[0143] In some embodiments, a concentration of the isotope target precursor is provided in the at least one element 502 to generate a power loss below a threshold compared to a fuel bundle 40 with a reference fuel element.

[0144] In some embodiments, the threshold is about 1-2%. In another embodiment the threshold is 1.7%.

[0145] In some embodiments, the reference element is an element comprising natural uranium.

[0146] In some embodiments, at least a second element 504 of the plurality of elements 500 compensates for the power loss.

[0147] According to an aspect, there is provided a fuel bundle 40 for producing medical isotopes during fuel burnup in a nuclear reactor 6. The fuel bundle 40 includes a medical isotope element 502 comprising at least one isotope target precursor configured to convert into at least one medical isotope when exposed to radiation and a plurality of fuel elements 504 comprising fissile material. An amount of the at least one isotope target precursor and fissile material in each of the plurality of fuel bundles 40 is selected to provide a desired burnup rate about equivalent to a reference fuel.

[0148] In some embodiments, the medical isotope element 502 is positioned centrally within the bundle 40 (e.g., at the center element 500a or the inner elements 500b), preferably the medical isotope element 502 is positioned at a center of the fuel bundle 40 (e.g., at the center element 500a).

[0149] In some embodiments, a rate of increase in the mass of the at least one medical isotope is configured to plateau after an initial mass production period during irradiation.

[0150] In some embodiments, the medical isotope element 502 having a composition of the at least one isotope in a range of up to 70%. In some embodiments, the medical isotope element 502 having a composition of the at least one isotope in a range of 1-70%.

[0151] In some embodiments, the fuel bundle 40 is a 37- or 43-element bundle.

[0152] In some embodiments, the fuel bundle 40 is a specifically modified bundle.

[0153] In some embodiments, a concentration of the isotope target precursor is provided in the medical isotope element 502 to generate a power loss below a threshold compared to a fuel bundle 40 with the reference fuel.

[0154] In some embodiments, the threshold is about 1.3-2%, preferably the threshold is about 1.7%.

[0155] In some embodiments, the plurality of fuel elements 504 comprises an amount of fissile material to compensate for the power loss.

[0156] In some embodiments, the reference fuel is natural uranium or slightly enriched uranium having a 0.9-2 wt% LI235.

[0157] NO FUEL ELEMENT EMBODIMENT

[0158] FIG. 6B is a cross-sectional view of an assembly 41 with a medical isotope element 502, according to some embodiments.

[0159] In a further embodiment, there may be no fuel elements 504 within the assembly 41 . In such a construction, one or more elements 500 can include the isotope target precursor (e.g., act as medical isotope elements 502). In some embodiments (for example, as illustrated), there may be no other elements 500 within the assembly 41 other than the medical isotope elements 502. In such embodiments, the medical isotope element(s) 502 may be supported by a support 501 within the bundle. This support 501 may be useful to position the element 502 within the central position within the assembly 41 (e.g., similarly positioned as center element position 500a in the bundle 40). The exterior of the assembly 41 may be configured in a manner consistent with fuel bundles 40 for the heavy water nuclear reactor 6 to ensure that the assembly 41 is still usable within the fuel channel assembly 28. For example, some of the fuel channel assemblies 28 may be able to receive the described assembly 41 instead of a fuel bundle 40 (e.g., that contains or does not contain one or more medical isotope elements 502).

[0160] In some embodiments, the assembly 41 may be configured similar to the fuel bundle 40 of FIG. 6A, but all elements 500 either include the isotope target precursor (e.g., they act as medical isotope elements 502) or they include a dummy composition (dummy elements). The dummy composition may not be fissile (and therefore may not act as a fuel element 504) and the dummy composition may not be an isotope target precursor (and therefore not act as a medical isotope element 502). Such bundles 41 may be beneficial to keep the processing of the assembly41 similar to other fuel bundles 40 which contain the isotope target precursor. For example, this may enable the medical isotopes to be extracted without requiring additional or different harvest steps to deal with the presence of the support 501 .

[0161] Some advantages of using a no fuel assembly 41 is that it does not violate nonproliferation treaties, the designs can be applied to small-scale isotope production, and the design may provide a quicker turnaround for harvesting with careful design (e.g., having no fissile materials means the assembly 41 may impact the overall power production of the core less than a bundle 40 with fissile material). The number of fuel assemblies 28 with a no fuel assembly 41 may be limited based on expected power deration and perturbation to the core depending on the neutron absorption depth. Furthermore, the design may be configured to limit the impact on neighboring fuel bundles 40.

[0162] According to an aspect, there is provided an assembly 41 comprising an element 502 for producing medical isotopes during fuel burnup in a heavy water nuclear reactor. The element 502 includes at least one isotope target precursor for converting the at least one isotope target precursor to a medical isotope when exposed to radiation. A concentration of the isotope target precursor is provided in the element. The assembly 41 is free of fissile fuel material.

[0163] In some embodiments, a rate of increase in the mass of the medical isotope is configured to plateau after an initial mass production period during irradiation.

[0164] In some embodiments, the radiation comprises neutron, alpha, beta, and / or gamma radiation.

[0165] In some embodiments, the nuclear reactor is a CANDU-type nuclear reactor 6.

[0166] In some embodiments, the medical isotope comprises a radioactive medical isotope.

[0167] In some embodiments, the medical isotope includes at least one of Bismuth-213, Caesium-131 , Caesium-137, Chromium-51 , Cobalt-60, Dysprosium-165, Erbium-169, Holmium- 166, lodine-125, lodine-131 , lridium-192, Iron-59, Lead-212, Lutetium-177, Molybdenum-99, Palladium-103, Phosphorus-32, Potassium-42, Radium-223, Rhenium-186, Rhenium-188, Samarium-153, Scandium-47, Selenium-75, Sodium-24, Strontium-89, Technetium-99m, Thorium-227, Xenon-133, Ytterbium-169, Ytterbium-177, progenitor of Lu-177, Yttrium-90, and Hydrogen-3 (Tritium).

[0168] In some embodiments, the isotope target precursor and the medical isotope are neutron absorbing materials having a thermal neutron capture cross-section of less than or equal to 100 barns, preferably less than or equal to 1 barns, more preferably less than or equal to 0.04 barns.

[0169] In some embodiments, the isotope target precursor or the medical isotope is a high neutron absorbing material, wherein the high neutron absorbing material is provided in a smaller volume than a comparable low neutron absorbing material to reduce the impact on the nuclear reactor 6.

[0170] In some embodiments, the at least one isotope target precursor comprises a plurality of isotope target precursors.

[0171] In some embodiments, the assembly 41 comprises support members 501 for positioning the element 502 in a fuel channel of the nuclear reactor 6.

[0172] EXEMPLARY METHOD TO PRODUCE MEDICAL ISOTOPES

[0173] FIG. 7 illustrates a schematic process diagram for a method of producing medical isotopes 600, according to some embodiments.

[0174] According to an aspect, there is provided a process 600 to produce medical isotopes during fuel burnup in a nuclear reactor. The process 600 includes providing an element 502 or a fuel bundle 40 containing an isotope target precursor that will convert to a medical isotope when irradiated in the core (block 602), burning the element 502 or fuel bundle 40 in the nuclear reactor 6 (block 604), removing the element 502 or fuel bundle 40 from the reactor 6 after burnup (block 606), and harvesting the medical isotopes from the element 502 or fuel bundle 40 (block 608).

[0175] In some embodiments, the element 502 or fuel bundle 40 is removed while the nuclear reactor 6 is online.

[0176] In some embodiments, most or all fuel bundles 40 in the nuclear reactor include the isotope target precursor in the center element 500a.

[0177] SYSTEM AND METHOD FOR MULTIPLE MEDICAL ISOTOPE PRODUCTION IN HEAVY WATER REACTOR

[0178] FIG. 9A is a schematic view of an example reactor 6 and fueling machines 7, according to some embodiments.

[0179] Fueling machines 7 may move to position a fuel bundle into a fuel channel assembly 28 of reactor 6 or receive a fuel bundle from the opposing end of the fuel channel once it is spent (i.e. once it has reached a desired burnup). The fueling machine 7 may include a fueling machine carriage and suspension 8. These components provide a system for medical radioisotope production. The system comprises reactor 6 comprising a plurality of fuel channel assemblies 28 which may be filled with a plurality of fuel bundles 40 (or no fuel assemblies 41). Each fuel bundle 40 may comprises a plurality of elements 500, where a first element 502 of the plurality of elements 500 of each of the plurality of fuel bundles 40 comprise at least one isotope target precursor configured to be converted into a medical radioisotope (medical isotope elements 502). The remaining elements 504 of the plurality of elements 500 comprise fissile material (fuel elements 504). The amount of the isotope target precursor(s) and fissile material in each fuel bundle 40 is selected to provide a desired burnup rate about equal to a reference fuel. In an embodiment, the reference fuel may be a natural uranium fuel bundle. The system may comprise at least one fuelling machine 7 for inserting the plurality of fuel bundles 40 (or no fuel assemblies 41) in the plurality of fuel channel assemblies 28 in a first mode of operation and receive the plurality of fuel bundles 40 once spent (or no fuel assemblies 41 once irradiated) in a second mode of operation. The fuelling machine 7 may move relative to a face of reactor 6 via bridge which provides a platform which moves to position the fuelling machine adjacent to a desired fuel channel assembly.

[0180] In an embodiment, the first element 502 of each of the plurality of fuel bundles 40 is positioned at a core element position (e.g., inner element position 500b or center element position 500a) of each of the plurality of fuel bundles 40 such that first element 502 is surrounded by other elements 504 comprising fissile material. In another embodiment, the first element 502 is positioned at a center 500a of each of the plurality of fuel bundles 40. The first element 502 of each fuel bundle 40 may comprise a plurality of isotope target precursors such that one or more medical isotopes can be produced from a single fuel bundle 40.

[0181] In another embodiment, a mass of the isotope target precursor in first element 52 of each of the plurality of fuel bundles 40 is selected to provide about equal reactivity decay for each of the plurality of fuel bundles 40. As shown in FIG. 10, a chart comparing k-infinity to bundle burnup for a plurality of example fuel bundle according to this disclosure each of which comprise the medical isotopes Lutetium-177 (Lu177), Molybdenum-99 (Mo99), Strontium-89 (St89), Yttrium-90 (Y90), lodine-131 (1131), and a reference material. The reference material was selected to be natural uranium in this example. FIG. 10 shows the balanced reactivity propertiesof the fuel bundles each comprising different isotopes where each of the plurality of fuel bundles has about the same k-infinity to burnup ratio. The properties of the five different isotope target precursor materials were all adjusted to be similar to the reference fuel so as to make each bundle behave in the same way as the reference fuel. In this example, the design allowance of the reactivity deviation for each fuel bundle is about 1 mk compared to the reference fuel in the example, which corresponds to a code and fuel specification uncertainty level. In an embodiment, the reactivity deviation for each fuel bundles is 0-2 mk.

[0182] Table 2 shows the time-average result of an example medical isotope core 502 compared with a reference core of natural uranium, where the property (maximum and average power level, etc.) can be maintained as the same level. The difference of refuelling impact is to be also very minor which demonstrates that the transition between the reference fuel and any medical isotope fuel bundle may be very smooth. This may result in the supply control of medical isotopes not being an issue. That is, if a certain isotope is needed more, the bundles can be loaded. Then, if the demand for a medical isotope decreases, the fuel bundles can be easily replaced by a normal fuel bundle.

[0183] Table 2: Time-average result of an example fuel bundles with a medical isotope core 502 compared with a reference core.

[0184] In an embodiment, at least one fuelling machine 7 inserts the plurality of fuel bundles 40 into one or more fuel channel assemblies 28 of the nuclear reactor 6 to be reacted concurrently to provide medical isotopes in each of the fuel bundles 40. In an example, fuel bundles 40 are inserted into one of the plurality of fuel channel assemblies 28; greater than 25% of fuel channel assemblies 28; greater than 50% fuel channel assemblies 28; greater than 75% of fuel channel assemblies 28; or all of fuel channel assemblies 28 for concurrent reaction within nuclear reactor 6. The assemblies 28 which have been provided with a fuel bundle 40 with a medical isotope element can be referred to as a medical isotope assembly.

[0185] In an embodiment, fuelling machine 7 is configured to remove the plurality of fuel bundles 40 at a desired exit burnup of the fissile material. Because the reactivity decay of each of fuel bundles 40 is similar to a reference bundle, the performance of each bundle 40 is predictable and can be managed during burnup until the reactivity of the fissile material in each fuel bundle 40 has been depleted to a point at which it will be removed from the reactor. A benefit of fuel bundle 40 described herein is that it can be left in the nuclear reactor until the desired exit burnup of the fissile material is reached rather than having to remove the medical isotopes before the fissile material in fuel bundles 40 has been depleted (e.g., until the medial isotope assembly becomes a “mature” medical isotope assembly).

[0186] FIG. 9B shows a schematic view of a cross-section of a nuclear reactor 6 divided into zones for production of distinct medical isotopes, according to some embodiments.

[0187] The first group of fuel bundles 40 are inserted into fuel channel assemblies 28 to define a first zone Z1 defined by a first distance range from a center of the heavy water nuclear reactor 6. The second group of fuel bundles 40 are inserted into fuel channel assemblies 28 to define a second zone Z2 defined by a second distance range from a center of the heavy water nuclear reactor 6. In an example, the first distance range is non-overlapping with the second distance range such that isotope target precursors in first zone Z1 and second zone Z2 are exposed to different neutron flux concentrations in reactor 6. Specifically, neutron flux will be greater toward the center of the reactor 6 and may decrease moving radially outward from the center of the reactor 6. In FIG. 9B, five zones Z1 , Z2, Z3, Z4, Z5 are illustrated; although the fuel bundles 40 comprising the same isotope target precursor may be grouped in more or fewer zones. In the illustrated example, first zone Z1 , second zone Z2, third zone Z3, fourth zone Z4, fifth zone Z5 may comprise fuel bundles 40 having isotope target precursor to form lodine-131 , Lutetium-177, Yttrium-90, Molybdenum-99, and Strontium-89 respectively. While FIG. 9B shows each channel 28 is loaded with a single type of isotope target precursor, the systems and method of this disclosure are not limited to this arrangement. That is, different types of isotope target precursor can be loaded in a single fuel channel assembly 28, where each fuel bundle has a certain type of isotope target precursor. The kinds of isotopes are not also limited and recognized as flexible.

[0188] In some embodiments, an isotope target precursor of a desired medical radioisotope having stronger neutron absorption is positioned closer to the center of the nuclear reactor’s inner core region, which has higher power and neutron flux in comparison to parts of the reactor further radially spaced from the center, to help control and balance the power and neutron flux within thereactor more naturally. In an example, it may be advantageous to position an isotope target precursor (and its resulting medical isotope) having a higher neutron absorption in a zone closer to the center of the core of the nuclear reaction (e.g., the first zone Z1) than an isotope target precursor (and its resulting medical isotope) having a smaller neutron absorption. In other words, it may be advantageous to position medical isotope target(s) and their precursor(s), having lower neutron absorption radially further away from the center of the nuclear reactor (e.g., the fifth zone Z5) than medical isotope target(s) and their precursor(s) having higher neutron absorption. Continuing the example, the first zone Z1 and the second zone Z2, shown in FIG. 9B, which may house medical isotope target(s) and their precursor(s) having similar neutron cross sections (e.g. lodine-131 and Lutetium-177) may be positioned closer to the center of the nuclear reactor than third zone Z3 which may contain a medical isotope and its precursor (e.g. Yttrium-90) with a smaller neutron cross section. The half-life of some example isotopes are listed in Table 3 and total neutron cross sections are compared in FIG. 11.

[0189] Table 3: Property of Medical Isotopes in Exampled Core

[0190] In an embodiment, the isotope target precursor(s) may be configured to be converted into any of: Bismuth-213, Caesium-131 , Caesium-137, Chromium-51 , Cobalt-60, Dysprosium- 165 , Erbium-169, Holmium-166, lodine-125, and brain), lodine-131 , lridium-192, Iron-59, Lead- 212, Lutetium-177, Molybdenum-99, Palladium-103, Phosphorus-32, Potassium-42, Radium- 223, Rhenium-186, Rhenium-188, Samarium-153, Scandium-47, Selenium-75, Sodium-24, Strontium-89, Technetium-99m, Thorium-227, Xenon-133, Ytterbium-169, Ytterbium- 177, progenitor of Lu-177, Yttrium-90, and Tritium (H3).

[0191] According to an aspect, there is provided a system for medical isotope production in a heavy water nuclear reactor. The system includes the heavy water nuclear reactor 6 comprising a plurality of fuel channel assemblies 28 (e.g., fuel channel assemblies 28 with fissile material therein and no medical isotope precursor), a plurality of medical isotope assemblies 28 (e.g., fuel channel assemblies 28 with medical isotope precursor therein) each comprising a medical isotope precursor configured to convert into at least one medical isotope when exposed to radiation, and at least one fuelling machine 7 configured to insert the plurality of medical isotope assemblies 28 into at least one of the plurality of fuel channel assemblies 28 in a first mode of operation and remove the plurality of medical isotope assemblies 28 from the plurality of fuel channel assemblies 28 once spent in a second mode of operation. The at least one fuelling machine 7 is configured to position the plurality of medical isotope assemblies 28 in at least one of the plurality of fuel channel assemblies 28 in the first mode of operation. After a rate of increase in the mass of the at least one medical isotope of at least one of the plurality of medical isotope assemblies 28 plateaus during irradiation forming at least one mature medical isotope assembly, the second mode of operation begins and the at least one mature medical isotope assembly is removed from the at least one fuel channel of the heavy water nuclear reactor 6.

[0192] In some embodiments, the at least one fuelling machine 7 is configured to insert the plurality of assemblies 28 into at least two or more of the plurality of fuel channel assemblies 28 for concurrent production of medical isotopes.

[0193] In some embodiments, the plurality of medical isotope assemblies 28 comprise at least one of the fuel bundle 40 as described above and / or the assembly 41 as described above.

[0194] In some embodiments, the plurality of medical isotope assemblies 28 comprise at least one of the fuel bundle 40 as described above, and each of the plurality of fuel bundles 40 has about the same k-infinity to burnup ratio.

[0195] In some embodiments, a mass of the isotope target precursor is selected to provide about equal reactivity decay for each of the plurality of fuel bundles 40.

[0196] In some embodiments, the at least one fuelling machine 7 is configured to remove the plurality of fuel bundles 40 at a desired exit burnup of the fissile material after the at least one mature medical isotope assembly is formed.

[0197] In some embodiments, the at least one fuelling machine 7 inserts the plurality of medical isotope assemblies 28 in at least one of: greater than 25% of the plurality of fuel channel assemblies 28; greater than 50% of the plurality of fuel channel assemblies 28; greater than 75% of the plurality of fuel channel assemblies 28; or all of the plurality of fuel channel assemblies 28, for concurrent reaction within the heavy water nuclear reactor 6.

[0198] In some embodiments, the plurality of medical isotope assemblies 28 includes a first group of medical isotope assemblies 28 each having a first isotope target precursor and a second group of medical isotope assemblies 28 having a second isotope precursor. The first group of medical isotope assemblies are inserted into the plurality of fuel channel assemblies 28 to define a first zone Z1 defined by a first distance range from a center of the heavy water nuclear reactor 6. The second group of medical isotope assemblies 28 are inserted into the plurality of fuel channel assemblies 28 to define a second zone Z2 defined by a second distance range from a center of the heavy water nuclear reactor 6. The first distance range is non-overlapping with the second distance range.

[0199] In some embodiments, a neutron cross section of a first medical radioisotope produced from the first isotope target precursor in the first zone Z1 is greater than the neutron cross section of a second medical radioisotope produced from the second isotope target precursor in the second zone Z2.

[0200] FIG. 12 shows a schematic diagram illustrating a method 1200 for medical radioisotope production in a heavy water nuclear reactor, according to some embodiments.

[0201] At 1202, the method 1200 comprises providing a plurality of fuel bundles 40 each comprising a plurality of elements 500. A first element 502 of the plurality of elements 500 of each of the plurality of fuel bundles 40 comprises at least one isotope target precursor configured to be converted into a medical radioisotope, and the remaining elements 504 of the plurality of elements 500 comprise fissile material (e.g., to act as fuel elements 504). An amount of the at least one isotope target precursor and fissile material in each of the plurality of fuel bundles 40 is selected to provide a desired burnup rate about equal to a reference fuel, such as natural uranium (e.g. a natural uranium 37M bundle). In an embodiment, the first element 502 of each of the plurality of fuel bundles 40 is positioned at a core (e.g., center element position 500a or inner element position 500b) of each of the plurality of fuel bundles 40, preferably the first element 502 is positioned at a center (e.g., center element position 500a) of each of the plurality of fuel bundles40. In another embodiment, a mass of the isotope target precursor in the first element of each of the plurality of fuel bundles 40 is selected to provide about equal reactivity decay for each of the plurality of fuel bundles. In an example, each of the plurality of fuel bundles 40 has about the same k-infinity to burnup ratio. In another embodiment, the first element 502 of the plurality of elements 500 of each of the plurality of fuel bundles 40 comprises a plurality of isotope target precursors.

[0202] At 1204, the method 1200 comprises inserting the plurality of fuel bundles 40 into at least one fuel channel assembly 28 of the heavy water nuclear reactor 6.

[0203] At 1206, the method 1200 comprises irradiating the plurality of fuel bundles 40 to convert the at least one isotope target precursor into a medical radioisotope.

[0204] At 1208, the method 1200 comprises removing the plurality of fuel bundles 40 from the fuel channel assemblies 28 of the heavy water nuclear reactor 6. In an embodiment, the removal of the plurality of fuel bundles 40 from the heavy water nuclear reactor 6 occurs when the plurality of fuel bundles 40 are at a desired exit burnup of the fissile material.

[0205] In an embodiment, method 1200 comprises inserting the plurality of fuel bundles 40 into: greater than 25% of the plurality of fuel channel assemblies 28; greater than 50% of the plurality of fuel channel assemblies 28; greater than 75% of the plurality of fuel channel assemblies 28; or all of the plurality of fuel channel assemblies 28, and concurrently irradiating the plurality of fuel bundles 40 within the heavy water nuclear reactor 6 to convert the at least one isotope target precursor of each bundles into the medical radioisotope.

[0206] In an embodiment, the plurality of fuel bundles 40 comprises: a first group of fuel bundles 40 having a first isotope target precursor; and a second group of fuel bundles 40 having a second isotope precursor. The method 1200 comprises: inserting the first group of fuel bundles 40 into the plurality of fuel channel assemblies 28 to define a first zone Z1 defined by a first distance range from a center of the heavy water nuclear reactor 6, and inserting the second group of fuel bundles 40 into the plurality of fuel channel assemblies 28 to define a second zone Z2 defined by a second distance range from a center of the heavy water nuclear reactor 6. The first distance range may not overlap with the second distance range. In an example, a neutron absorption (or neutron cross section) of a first medical radioisotope produced from the first isotope target precursor in the first zone Z1 is greater than the neutron absorption (or neutron cross section) ofa second medical radioisotope produced from the second isotope target precursor in the second zone Z2.

[0207] In an embodiment, at least one isotope target precursor used in method 1200 may be configured to be converted into any of: Bismuth-213, Caesium-131 , Caesium-137, Chromium-51 , Cobalt-60, Dysprosium-165 , Erbium-169, Holmium-166, lodine-125, and brain), lodine-131 , lridium-192, Iron-59, Lead-212, Lutetium-177, Molybdenum-99, Palladium-103, Phosphorus-32, Potassium-42, Radium-223, Rhenium-186, Rhenium-188, Samarium-153, Scandium-47, Selenium-75, Sodium-24, Strontium-89, Technetium-99m, Thorium-227, Xenon-133, Ytterbium- 169, Ytterbium-177, progenitor of Lu-177, Yttrium-90, and Tritium (H3).

[0208] FIG. 13 shows a schematic diagram illustrating a method 1300 for medical radioisotope production in a heavy water nuclear reactor.

[0209] According to an aspect, there is provided a method 1300 of producing medical isotopes during fuel burnup in a heavy water nuclear reactor 6. The method 1300 includes providing the fuel bundle 40 as described above or the assembly 41 as described above in the heavy water nuclear reactor 6 (block 1302), irradiating the fuel bundle 40 or the assembly 41 in the heavy water nuclear reactor 6 (block 1304), removing the fuel bundle 40 or the assembly 41 from the heavy water reactor (block 1306), and harvesting the at least one medical isotope from the fuel bundle 40 or the assembly 41 (block 1308).

[0210] In some embodiments, the method 1300 includes providing a plurality of the fuel bundles 40 as described above. Each of the plurality of fuel bundles 40 has about the same k-infinity to burnup ratio.

[0211] In some embodiments, a mass of the isotope target precursor is selected to provide about equal reactivity decay for each of the plurality of fuel bundles 40.

[0212] In some embodiments, the fuel bundle 40 or the assembly 41 is removed from the heavy water nuclear reactor 6 at a desired exit burnup of the fissile material after the at least one mature medical isotope assembly is formed.

[0213] In some embodiments, the fuel bundle 40 or the assembly 41 is removed while the nuclear reactor 6 is online.

[0214] IMPLEMENTATION DETAILS

[0215] The following discussion provides many example embodiments. Although each embodiment represents a single combination of inventive elements, other examples may include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, other remaining combinations of A, B, C, or D, may also be used.

[0216] Although the embodiments have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope as defined by the appended claims.

[0217] Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps

[0218] As can be understood, the examples described above and illustrated are intended to be exemplary only. The scope is indicated by the appended claims.

[0219] The claims are not intended to include, and should not be interpreted to include, means- plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.

Claims

WHAT IS CLAIMED IS:

1. A fuel bundle for producing medical isotopes during fuel burnup in a nuclear reactor, the fuel bundle comprising: a medical isotope element comprising at least one isotope target precursor configured to convert into at least one medical isotope when exposed to radiation, a plurality of fuel elements comprising fissile material, wherein an amount of the at least one isotope target precursor and fissile material in each of the plurality of fuel bundles is selected to provide a desired burnup rate about equivalent to a reference fuel.

2. The fuel bundle of claim 1 , wherein the medical isotope element is positioned centrally within the bundle, preferably the medical isotope element is positioned at a center of the fuel bundle.

3. The fuel bundle of any one of claims 1 to 2, wherein a rate of increase in the mass of the at least one medical isotope is configured to plateau after an initial mass production period during irradiation.

4. The fuel bundle of any one of claims 1 to 3, the medical isotope element having a composition of the at least one isotope in a range of up to 70%; optionally the medical isotope element having a composition of the at least one isotope in a range of 1-70%.

5. The fuel bundle of any one of claims 1 to 4, wherein the fuel bundle is a 37- or 43-element bundle.

6. The fuel bundle of any one of claims 1 to 4, wherein the fuel bundle is a specifically modified bundle.

7. The fuel bundle of any one of claims 1 to 6, wherein a concentration of the isotope target precursor is provided in the medical isotope element to cause a power loss below a threshold compared to a fuel bundle with the reference fuel.

8. The fuel bundle of claim 7, wherein the threshold is about 1.3-2%, preferably the threshold is about 1.7%.

9. The fuel bundle of any one of claims 7 to 8, wherein the plurality of fuel elements comprises an amount of fissile material to compensate for the power loss.

10. The fuel bundle of any one of claims 1 to 9, wherein the reference fuel is natural uranium or slightly enriched uranium having a 0.9-2 wt% LI235.

11. An assembly comprising an element for producing medical isotopes during fuel burnup in a heavy water nuclear reactor, the element comprising: at least one isotope target precursor, for converting the at least one isotope target precursor to a medical isotope when exposed to radiation, wherein a concentration of the isotope target precursor is provided in the element, and wherein the assembly is free of fissile fuel material.

12. The assembly of claim 11 , wherein a rate of increase in the mass of the medical isotope is configured to plateau after an initial mass production period during irradiation.

13. The assembly of any one of claims 11 to 12, wherein the radiation comprises soft neutron; optionally wherein the radiation comprises alpha, beta, and / or gamma radiation.

14. The assembly of any one of claims 11 to 13, wherein the nuclear reactor is a CANDU-type nuclear reactor.

15. The assembly of any one of claims 11 to 14, wherein the medical isotope comprises a radioactive medical isotope.

16. The assembly of any one of claims 11 to 15, wherein the medical isotope comprises at least one of Bismuth-213, Caesium-131 , Caesium-137, Chromium-51 , Cobalt-60, Dysprosium-165, Erbium-169, Holmium-166, lodine-125, lodine-131 , lridium-192, Iron-59, Lead-212, Lutetium-177, Molybdenum-99, Palladium-103, Phosphorus-32, Potassium-42, Radium-223, Rhenium-186, Rhenium-188, Samarium-153, Scandium-47, Selenium-75, Sodium-24, Strontium-89, Technetium-99m, Thorium-227, Xenon-133, Ytterbium- 169, Ytterbium-177, progenitor of Lu-177, Yttrium-90, and Hydrogen-3 (Tritium).

17. The assembly of any one of claims 11 to 16, wherein the isotope target precursor or the medical isotope is a high neutron absorbing material, wherein the high neutron absorbing material is provided in a smaller volume than a comparable low neutron absorbing material to reduce the impact on the nuclear reactor.

18. The assembly of any one of claims 11 to 17, wherein the at least one isotope target precursor comprises a plurality of isotope target precursors.

19. The assembly of any one of claims 11 to 18, wherein the assembly comprises support members for positioning the element in a fuel channel of the nuclear reactor.

20. A system for medical isotope production in a heavy water nuclear reactor, the system comprising: the heavy water nuclear reactor comprising a plurality of fuel channel assemblies; a plurality of medical isotope assemblies each comprising a medical isotope precursor configured to convert into at least one medical isotope when exposed to radiation; at least one fuelling machine configured to insert the plurality of medical isotope assemblies into at least one of the plurality of fuel channel assemblies in a first mode of operation and remove the plurality of medical isotope assemblies from the plurality of fuel channel assemblies once spent in a second mode of operation, wherein the at least one fuelling machine is configured to position the plurality of medical isotope assemblies in at least one of the plurality of fuel channel assemblies in the first mode of operation, wherein, after a rate of increase in the mass of the at least one medical isotope of at least one of the plurality of medical isotope assemblies plateaus during irradiation forming at least one mature medical isotope assembly, the second mode of operation begins and the at least one mature medical isotope assembly is removed from the at least one fuel channel of the heavy water nuclear reactor.

21. The system of claim 20, wherein the at least one fuelling machine is configured to insert the plurality of assemblies into at least two or more of the plurality of fuel channel assemblies for concurrent production of medical isotopes.

22. The system of any one of claims 20-21 wherein the plurality of medical isotope assemblies comprise at least one of the fuel bundle according to any one of claims 1 to 10 and the assembly of any one of claims 11 to 19.

23. The system of claim 22, wherein the plurality of medical isotope assemblies comprise at least one of the fuel bundle according to any one of claims 1 to 10, and each of the plurality of fuel bundles has about the same k-infinity to burnup ratio.

24. The system of claim 23, wherein a mass of the isotope target precursor is selected to provide about equal reactivity decay for each of the plurality of fuel bundles.

25. The system of any one of claims 22 to 24, wherein the at least one fuelling machine is configured to remove the plurality of fuel bundles at a desired exit burnup of the fissile material after the at least one mature medical isotope assembly is formed.

26. The system of any one of claims 20 to 25, wherein the at least one fuelling machine inserts the plurality of medical isotope assemblies in at least one of: one of the plurality of fuel channel assemblies; greater than 25% of the plurality of fuel channel assemblies; greater than 50% of the plurality of fuel channel assemblies; greater than 75% of the plurality of fuel channel assemblies; or all of the plurality of fuel channel assemblies, for concurrent reaction within the heavy water nuclear reactor.

27. The system of any one of claims 20 to 26, wherein the plurality of medical isotope assemblies comprise: a first group of medical isotope assemblies each having a first isotope target precursor; a second group of medical isotope assemblies having a second isotope precursor; wherein the first group of medical isotope assemblies are inserted into the plurality of fuel channel assemblies to define a first zone defined by a first distance range from a centerof the heavy water nuclear reactor, and wherein the second group of medical isotope assemblies are inserted into the plurality of fuel channel assemblies to define a second zone defined by a second distance range from a center of the heavy water nuclear reactor, wherein the first distance range is non-overlapping with the second distance range.

28. The system of claim 27, wherein a neutron cross section of a first medical radioisotope produced from the first isotope target precursor in the first zone is greater than the neutron cross section of a second medical radioisotope produced from the second isotope target precursor in the second zone.

29. A method of producing medical isotopes during fuel burnup in a heavy water nuclear reactor, the method comprising: providing the fuel bundle according to of any one of claims 1 to 10 or the assembly of any one of claims 11 to 19 in the heavy water nuclear reactor; irradiating the fuel bundle or the assembly in the heavy water nuclear reactor; removing the fuel bundle or the assembly from the heavy water reactor; and harvesting the at least one medical isotope from the fuel bundle or the assembly.

30. The method of claim 29, comprising providing a plurality of the fuel bundles according to any one of claims 1 to 10, wherein each of the plurality of fuel bundles has about the same k-infinity to burnup ratio.31 . The method of any one of claims 29 to 30, wherein a mass of the isotope target precursor is selected to provide about equal reactivity decay for each of the plurality of fuel bundles.

32. The system of any one of claims 29 to 31 , wherein the fuel bundle or the assembly is removed from the heavy water nuclear reactor at a desired exit burnup of the fissile material after the at least one mature medical isotope assembly is formed.

33. The method of any one of claims 29 to 32, wherein the fuel bundle or the assembly is removed while the nuclear reactor is online.

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