CA3207357A1

CA3207357A1 - Irradiation target containing support rod for producing mo-99 isotope in heavy water reactor

Info

Publication number: CA3207357A1
Application number: CA3207357A
Authority: CA
Inventors: Junqiang LU; Fuliang CHEN; Yu Han; Yang DING; Xiangyu WEI; Yunqing ZHOU
Original assignee: Shanghai Nuclear Engineering Research and Design Institute Co Ltd
Current assignee: Shanghai Nuclear Engineering Research and Design Institute Co Ltd
Priority date: 2021-02-02
Filing date: 2022-04-02
Publication date: 2022-08-11
Also published as: WO2022167008A1; CN112951472B; CN112951472A

Abstract

An irradiation target containing a support rod for producing a molybdenum-99 isotope in a heavy water reactor, comprising: a plurality of fuel elements (1), at least one of which comprising a support rod (14) having at least two through holes, the through holes being arranged along an axial direction of the support rod (14); enriched uranium cores (13) provided in the through holes; end plates (2) provided at both ends of the fuel elements (1) and fixedly connected to the plurality of fuel elements (1). A plurality of fuel elements (1) are provided. The enriched uranium cores (13) use a rich uranium fuel having a 235U enrichment degree 15.0 wt% - 20.0 wt%. By means of the present invention, existing reactors may be utilized for non-stop production of 99Mo having a short half-life. By using enriched uranium to produce 99Mo, the efficiency is high and the quality is good. Meanwhile, effects on power generation of a nuclear power plant can be reduced to a maximum extent.

Description

IRRADIATION TARGET CONTAINING SUPPORT ROD FOR
PRODUCING Mo-99 ISOTOPE IN HEAVY WATER REACTOR
TECHNICAL FIELD
[0001] The present application relates to the technical field of fission-type nuclear reactors, in particular to an irradiation target containing a support rod for producing Mo-99 isotope in a heavy water reactor.
BACKGROUND

[0002] Nuclear medicine is an indispensable and important subject in medicine, which plays a special role in the diagnosis and treatment of human diseases and has developed rapidly in recent years. Among others, 99mTc can be complexed with a variety of I igands to form a variety of organ and functional imaging agents, which can be used to diagnose various diseases and determine the changes in the function of human organs. According to the data of Nature News &
Comment, clinical diagnosis using 99mTc-related imaging technology reaches 30 million to 40 million person-times worldwide every year, accounting for 80% of all nuclear medicine applications.

[0003] The half-life of 99mTc is very short, which is only 6.02 hours, and 99mTc usually needs to be acquired in real time, at places where it is used, by decay of the parent isotope Mo-99 with a half-life of 66 hours. A device for producing 99mTc from Mo-99 is a molybdenum-technetium generator. That is, the isotope actually used by a hospital or nuclear dispensary is 99mTc, but the reactor produces and supplies Mo-99. According to the estimation of Nuclear Energy Corporation of South Africa (NECSA), the market of Mo-99 isotope is more than 5 billion US
dollars per year.

[0004] In recent years, Mo-99 isotope in global market is mainly supplied by five global suppliers including MDS Nordion in Canada, Mallinckrodt-Covidien in Netherlands, Institute National des Raioelements (IRE) in Belgium, Nuclear Technology Products (NTP) in South Africa, and the Australian Nuclear Science and Technology Organization (ANSTO) in Australia.
However, most of the research reactors or test reactors used by these suppliers were built in the 1950s and 1960s, which are seriously aging and are expected to be shut down successively from 2016 to 2030. In addition, most of them use high enriched uranium (HEU) targets with 235U
enrichment of over 90%. Since HEU may be used in the preparation of nuclear weapons and nuclear explosive devices, it is considered as a high-risk nuclear material.
The conversion from HEU to low enriched uranium (LEU) is advocated internationally to reduce global threats.

[0005] Compared with HEU targets, the production of Mo-99 by LEU
may lead to a decrease in product yield and an increase in production costs by almost 20%.
This change will have a certain impact on the global market supply of Mo-99. Therefore, on the one hand, countries around the world are comprehensively promoting the development of irradiation device construction projects, and on the other hand, they are constantly seeking new ways and methods to obtain Mo-99. BWX Technologies, Inc. (BWTX) in Canadian proposed a method for producing Mo-99 by a capture method in a heavy water reactor in CN111066095A
(April 24, 2020) and CN110462750A (November 15, 2019). Since the half-life of Mo-99 is very short, it must be separated and extracted for use as soon as possible after it is produced. Heavy water reactors can be refueled online, that is, refueling without shutdown, which has natural advantages for producing this isotope with a short-decay period.

[0006] However, since 98Mo is used during the production of Mo-99 by the capture method and the neutron absorption cross-section thereof has a very small area, which is generally only about 0.13 barn, the production of Mo-99 by the capture method has a disadvantage of low unit of production. Besides, due to the existence of M o-98 carrier, the Mo-99 produced has an inherent disadvantage of low specific activity, which may result in large elution volume and large generator volume, and thus it is difficult to meet medical requirements.
In addition, a target material used in the capture method is Mo-98, that is to say, once a fuel bundle in a selected fuel channel is replaced with a target mainly containing Mo-98, this target loses the function of the fuel original bundle generating heat through the chain nuclear fission reaction for power generation, thus affecting power generation of nuclear power plants.

[0007] Referring to FIG. 1, a conventional fuel bundle is generally a cylindrical assembly composed of 37 fuel elements 1 welded with two end plates 2 made of Zr-4.
Referring to FIG. 2, the fuel element 1 is mainly composed of a uranium-containing core 12, a cladding 11 made of Zr-4 and end plugs made of Zr-4. Among them, the cladding 11 has an outer diameter of 13.1 mm and an inner diameter of 12.3 mm, and the uranium-containing core 12 is implemented using natural abundance UO2 pellets with a diameter of 12.2 mm. The end plugs are welded to both ends of the cladding to seal the fuel elements. The end plate and the end plugs of the fuel element are also connected by welding. A positioning spacer is welded at the middle of each fuel element, so that a gap can be maintained between adjacent fuel elements by contact of the positioning spacers of adjacent fuel elements after the fuel element is loaded into the bundle. For the peripheral fuel elements, support spacers 3 are additionally provided at both ends close to the outside and the middle thereof to maintain a gap between the fuel bundle and a pressure tube.

[0008] The UO2 pellets in conventional fuel bundles are made of natural abundance ceramic UO2 powder which is pressed and sintered at high temperature to form a cylindrical shape. The abundance of 235U in natural uranium is 0.71 wt% 235.0 is .
prone to fission reactions under neutron irradiation, and the distribution of its fission products forms two humps with atomic weights around 100 and 135. Referring to FIG. 3, Mo-99 is just in one of the humps, and its fission product share is as high as 6.13%. However, conventional fuel bundles use natural uranium, the content of 235U in natural uranium is too low, and the efficiency of directly extracting Mo-99 from conventional fuel bundle fission products is too low.
SUM MARY

[0009]
In order to overcome the above technical problems, the present application provides an irradiation target containing a support rod for producing Mo-99 isotope in a heavy water reactor, which can efficiently produce Mo-99 and facilitate the extraction of the produced Mo-99 in the later stage, while minimizing the impact on the power generation of nuclear power plants.

[0010]
An irradiation target containing a support rod for producing MO-99 isotope in a heavy water reactor according to the present application includes: a plurality of fuel elements, at least one of which includes the support rod having at least two through holes extending along an axial direction of the support rod; an enriched uranium core provided in the through holes; end plates provided at both ends of the fuel elements and fixedly connected to the plurality of fuel elements, wherein the enriched uranium core includes an enriched uranium fuel having 235U
enrichment of 15.0 wt% to 20.0 wt%.

[0011]
Preferably, the enriched uranium fuel is UO2, UN, UC, U35i2, U metal, U-Zr alloy, or U-Al alloy, or any combination of any of them with any one or more of industrial pure zirconium, zirconium alloy, industrial pure aluminum, aluminum alloy, industrial pure molybdenum, molybdenum alloy, industrial pure niobium, niobium alloy, stainless steel, nickel alloy, and silicon carbide.

[0012]
Preferably, the enriched uranium core is a solid enriched uranium rod, several stacked enriched uranium pellets, or enriched uranium powder; the enriched uranium core has a diameter of 0.5 mm to 7 mm, the support rod has an outer diameter of 10 mm to 14 mm, and a diameter of each through hole of the support rod is greater than or equal to the diameter of the enriched uranium core; and end plugs for sealing are provided at both ends of the through hole of the support rod.

[0013]
Preferably, the fuel element further includes a cladding sleeved on the support rod, and additional end plugs welded on both ends of the cladding for sealing; the enriched uranium core is a solid enriched uranium rod, several stacked enriched uranium pellets or enriched uranium powder; and the cladding has an outer diameter of 10 mm to 14 mm, the support rod has an outer diameter of 9 mm to 13 mm, the enriched uranium core has an diameter of 0.5 mm to 7 mm, an inner diameter of the cladding is greater than or equal to the outer diameter of the support rod, and an inner diameter of the support rod is greater than or equal to the diameter of the enriched uranium core.

[0014] Preferably, the support rod further has at least one through hole for filler, and a filling material is embedded in the through hole for filler to form a filler.

[0015] Preferably, the support rod is made of a material with a thermal neutron macroscopic absorption cross-section of less than 10 barns.

[0016] Preferably, the support rod is made of any one of the following nuclear-grade materials: zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, nickel-based alloy, aluminum oxide, and beryllium oxide.

[0017] Preferably, the cladding is made of a material with a thermal neutron macroscopic absorption cross-section of less than 10 barns.

[0018] Preferably, the cladding is made of any one of the following nuclear-grade materials:
zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, and nickel-based alloy.

[0019] Preferably, the filling material is a material with a thermal neutron macroscopic absorption cross-section of greater than 1 barn.

[0020] Preferably, the filling material is a material in which a mass percentage of depleted uranium, tungsten, boron, dysprosium, gadolinium, silver or hafnium is greater than 5%.

[0021] The irradiation target containing a support rod for producing Mo-99 isotope in a heavy water reactor according to the present application fully utilizes the characteristics of refueling without shutdown of the heavy water reactor, and utilizes existing reactors for non-stop production of Mo-99 with a short half-life without having to build new irradiation facilities specially. By the present invention, natural abundance UO2 pellets are replaced by enriched uranium, so as to gather 235U that is originally evenly distributed in the natural abundance UO2 pellets, and produce Mo-99 with high efficiency and good quality, that is, the specific activity is high. When producing Mc-99 by using the radiation targets according to the present application, the impact on the power generation of nuclear power plants can be reduced to the greatest extent.
BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to illustrate the technical solution of the embodiments of the present application more clearly, the accompanying drawing that needs to be used in the embodiments of the present application will be briefly introduced below. Obviously, the accompanying drawings described below only exemplify the specific embodiments of the present application, and those skilled in the art can obtain other embodiments according to the following figures without making creative efforts.

[0023] FIG. 1 is a three-dimensional schematic diagram of a conventional fuel bundle using natural uranium.

[0024] FIG. 2 is a cross-sectional diagram of the conventional fuel element shown in FIG. 1.

[0025] FIG. 3 is a plot of fission product yield vs. mass number of 235U after fission under neutron irradiation.

[0026] FIG. 4 is a cross-sectional diagram of a fuel element according to an embodiment of the present application.

[0027] FIG. 5 is a cross-sectional diagram of a fuel element including a cladding according to an embodiment of the present application.

[0028] FIG. 6 is a cross-sectional diagram of a fuel element including a filler and a cladding according to an embodiment of the present application.

[0029] In the drawings, each drawing is not drawn to scale.

[0030] Reference number list:
1- Fuel element 11- Cladding 12- Uranium-containing core 13- Enriched uranium core 14- Support rod 15- Filler 2- End plate 3- Support spacer DETAILED DESCRIPTION

[0031] The implementation manner of the present application will be further described in detail below with reference to the drawings and embodiments. The detailed description of the following embodiments and drawings are used to exemplarily illustrate the principles of the present application, but not to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0032] In the description of the present application, it should be noted that unless otherwise specified, the meaning of "a plurality of" is more than two; the orientation or positional relationship indicated by the terms "above", "below", "left", "right", "inner", "outside" and so on are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore cannot be understood as restrictions to this application. In addition, the terms "first", "second", "third", etc.
are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] The orientation words appearing in the following description are the directions shown in the drawings, and do not limit the specific structure of the present application. In the description of this application, it should also be noted that unless otherwise specified and limited, the terms "communication", "connection" and "couple" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integrated connection;
or it can be a direct connection, or an indirect connection through an intermediary. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

[0034] Referring to FIG. 4 and in conjunction with FIGS. 1 and 2, the irradiation target containing a support rod for producing MO-99 isotope in a heavy water reactor includes: a plurality of fuel elements 1, at least one of which includes a support rod 14 having at least two through holes extending along an axial direction of the support rod 14; an enriched uranium core 13, which is provided in the through holes; end plates 2, which are provided at both ends of the fuel elements 1 and fixedly connected to the plurality of fuel elements 1, wherein the enriched uranium core 13 includes an enriched uranium fuel having 235 U enrichment of 15.0 wt% to 20.0 wt%.

[0035] Further, the enriched uranium fuel is UO2, UN, UC, U3Si2, U metal, U-Zr alloy, or U-Al alloy or any combination of any of them with any one or more of industrial pure zirconium, zirconium alloy, industrial pure aluminum, aluminum alloy, industrial pure molybdenum, molybdenum alloy, industrial pure niobium, niobium alloy, stainless steel, nickel alloy, and silicon carbide.

[0036] Further, the support rod 14 is made of a material with a thermal neutron macroscopic absorption cross-section of less than 10 barns.

[0037] Further, the support rod 14 is made of any one of the following nuclear-grade materials: zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, nickel-based alloys, aluminum oxide, and beryllium oxide.

[0038] Different embodiments of the fuel element 1 are specifically described below.
Example 1

[0039] Referring to FIG. 4, in this example, the enriched uranium core 13 is a solid enriched uranium rod, several stacked enriched uranium pellets, or enriched uranium powder. The enriched uranium core 13 has a diameter of 0.5 mm to 7 mm, the support rod 14 has an outer diameter of 10 mm to 14 mm, and the diameter of the through hole of the support rod 14 is greater than or equal to the diameter of the enriched uranium core. End plugs for sealing are further provided at both ends of the through hole of the support rod 14.

[0040] Further, the enriched uranium core 13 is implemented using the enriched uranium core 13 formed by stacking UO2 pellets with 235U enrichment of 19.5 wt%, and the support rod 14 made of Zr-4 has three through holes. The three through holes are evenly distributed around the circle-center of the support rod 14 to form an equilateral triangle, and a distance between the circle-center of the through hole and the circle-center of the support rod 14 is 4 mm. The enriched uranium core 13 has a diameter of 1.6 mm and is tightly embedded in the through hole of the support rod 14. The support rod 14 has an outer diameter of 13.1 mm.
The reason that the through holes are evenly distributed in an equilateral triangle in this embodiment is as follows:
the thermal conductivity of the UO2 pellets is relatively low, while the high enrichment of 235U
of the enriched uranium core 13 leads to a large amount of heat generation, thus temperature of the enriched uranium core 13 by irradiating may be very high; if the enriched uranium cores 13 are arranged in one through hole together, the temperature thereof may be too high; and when the enriched uranium cores 13 are arranged separately in a plurality of through holes, heat generated can be dissipated, thereby reducing the temperature of the enriched uranium cores 13.

[0041] The enriched uranium core 13 can produce Mo-99 under neutron irradiation while providing a suitable calorific value. The 18 fuel elements 1 in the outermost circle of the irradiation target are implemented using the fuel elements 1 shown in FIG. 4, the 19 fuel elements in the inner three circles are implemented using the conventional fuel elements 1 shown in FIG. 2, and Mo-99 isotope produced by the single irradiation target has an intensity of radioactivity of 1000 Curies, i.e., a scale of 6 days or more (that is, the amount of remaining M o-99 after decaying for 6 days or more).

[0042] The reasons of the arrangement of the fuel element 1 containing an enriched uranium material in the outer circle of the irradiation target bundle are as follows:
the enriched uranium material needs to be used to extract Mo-99 in subsequent steps, and such arrangement may facilitate disassembly; in addition, such arrangement may subject to less self-shielding effect, so that nuclear reaction is more likely to occur.

[0043] The enriched uranium pellets in this example may also be replaced by enriched uranium powder, that is, the enriched uranium powder is put into the through holes of the support rod 14 and is compacted. Besides, it is also possible to directly replace several enriched uranium pellets with a single enriched uranium rod of UO2.
Example 2

[0044] Referring to FIG. 5, the fuel element 1 in this example further includes a cladding 11 sleeved on the support rod 14, and additional end plugs welded to both ends of the cladding 11 for sealing.

[0045] Further, the cladding 11 is made of a material with a thermal neutron macroscopic absorption cross-section of less than 10 barns.

[0046] Further, the cladding 11 is made of any one of the following nuclear-grade materials:
zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, and nickel-based alloy.

[0047] In this example, the enriched uranium core 13 is a solid enriched uranium rod, several stacked enriched uranium pellets, or enriched uranium powder. The cladding 11 has an outer diameter of 10 mm to 14 mm, the support rod 14 has an outer diameter of 9 mm to 13 mm, the enriched uranium core 13 has a diameter of 0.5 mm to 7 mm, the inner diameter of the cladding 11 is greater than or equal to the outer diameter of the support rod 14, and the inner diameter of the support rod 14 is greater than or equal to the diameter of the enriched uranium core 13.

[0048] Further, the support rod 14 having an outer diameter of 12.2 mm is wrapped with a cladding 11. In this example, the cladding 11 is a thin-walled tube made of Zr-4, with an inner diameter of 12.3 mm and an outer diameter of 13.1 mm.

[0049] The support rod 14 made of Zr-4 has three through holes, the three through holes are evenly distributed around the circle-center of the support rod 14 to form an equilateral triangle, and a distance between the circle-center of the through hole and the circle-center of the support rod 1-2 is 4 mm, Enriched uranium cores 13 formed by stacking UO2 pellets with enrichment of 19.5 wt% are tightly embedded in the three through holes, and the enriched uranium core 1-1 of UO2 has a diameter of 1.6 mm.

[0050] The enriched uranium core 13 can produce Mo-99 under neutron irradiation while providing a suitable calorific value. The 18 fuel elements in the outermost circle of the irradiation target are implemented using the fuel elements 1 shown in FIG. 5, the 19 fuel elements 1 in the inner three circles are implemented using the conventional fuel elements 1 shown in FIG. 2, and Mo-99 isotope produced by the single irradiation target has an intensity of radioactivity of 1000 Curies or above.

[0051] The enriched uranium pellets in this example may also be replaced by enriched uranium powder, that is, the enriched uranium powder is put into the through holes of the support rod 14 and is compacted. Besides, it is also possible to directly replace several enriched uranium pellets with a single enriched uranium rod of UO2.
Example 3

[0052] Referring to FIG. 6, there is at least one through hole for a filler 15 in the support rod 14 in this example, and a filling material is embedded in the through hole for the filler 15 to form the filler 15.

[0053] Further, the cladding 11 is made of a material with a thermal neutron macroscopic absorption cross-section of less than 10 barns.

[0054] Further, the cladding 11 is made of any one of the following nuclear-grade materials:
zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, and nickel-based alloy.

[0055] Further, the filling material is a material with a thermal neutron macroscopic absorption cross-section of greater than 1 barn.

[0056] Further, the filling material is a material in which a mass percentage of depleted uranium, tungsten, boron, dysprosium, gadolinium, silver or hafnium is greater than 5%.

[0057] The support rod 14 is made of a material with a thermal neutron macroscopic absorption cross-section of less than 10 barns. The support rod 14 is made of any one of the following nuclear-grade materials: zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, nickel-based alloy, aluminum oxide, and beryllium oxide. The cladding 11 is made of a material with a thermal neutron macroscopic absorption cross-section of less than 10 barns. The cladding 11 is made of any one of the following nuclear-grade materials:
zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, and nickel-based alloy. The filling material is a material with a thermal neutron macroscopic absorption cross-section of greater than 1 barn. The filling material includes a material in which a mass percentage of depleted uranium, tungsten, boron, dysprosium, gadolinium, silver or hafnium is greater than 5%.

[0058] Further, the support rod 14 having an outer diameter of 12.2 mm is wrapped with a cladding 11. In this example, the cladding 11 is a thin-walled tube made of Zr-4, with an inner diameter of 12.3 mm and an outer diameter of 13.1 mm.

[0059] The support rod 14 made of Zr-4 is provided with three through holes distributed evenly around the circle-center of the support rod 14, and a through hole for filler 15 is further provided at the circle-center of the support rod 14. A distance between the circle-center of the through hole and the circle-center of the support rod 14 is 4 mm.

[0060] The enriched uranium cores 13 with a diameter of 1.5 mm, which are formed by stacking UO2 pellets with 235U enrichment of 19.5 wt%, are tightly embedded in the three through holes, and the through hole for filler 15 is tightly embedded with a filler 15 with a diameter of 4.9 mm. The filler 15 is formed by stacking depleted uranium UO2 pellets with 235U
enrichment of 0.2 wt%.

[0061] The purpose of using the filler 15 in this example is to balance the uranium load (that is, the total amount of loaded uranium elements, including all U
isotopes such as 235U and 238u) in the bundle, so that the nuclear characteristics of the fuel bundle are unchanged with respect to the conventional fuel bundle. For this purpose, it is not enough to only ensure the amount of 235U, and a commensurate amount of 238U should also be ensured for the entire bundle.
Therefore, depleted uranium pellets with 238U as a main component are used as the material of the filler 15.

[0062] The enriched uranium core 13 can produce Mo-99 under neutron irradiation while providing a suitable calorific value. The 18 fuel elements in the outermost circle of the irradiation target are implemented using the fuel elements 1 shown in FIG. 6, and the 19 fuel elements in the inner three circles are implemented using the conventional fuel elements shown in FIG. 2, and Mo-99 isotope produced by the single irradiation target has an intensity of radioactivity of 1000 Curies or above.

[0063] The enriched uranium pellets in this example may also be replaced by enriched uranium powder, that is, the enriched uranium powder is put into the three through holes of the support rod 14 evenly distributed around the circle-center of the support rod 14 and is compacted.
It is also possible to directly replace several enriched uranium pellets with a single enriched uranium rod of UO2.

[0064] The core idea of the design principle of the present application is: when considering the neutron irradiation on enriched uranium, after the fission reaction occurs, separating Mo-99 from the target by radiochemical means is the most efficient production means.
Therefore, according to the technical solution of the present application, a part of the uranium-containing cores 12 of UO2 with natural abundance 235U in at least one of the fuel elements 1 is replaced with an enriched uranium material, so that the amount of 235U in the irradiation target of the present application is substantially the same as the amount of 235U in an existing conventional fuel bundle, thereby realizing that the nuclear characteristics and thermal performance of a substitute of the fuel bundle are basically unchanged and ensuring the safe and economical power generation of nuclear power plants. As the enrichment of 235U is increased, a large amount of 238U is removed, and the amount of uranium material is reduced; and the vacated space is supported or filled by other materials to realize the functions of positioning and heat transfer of 235U fissile materials. Feasible schemes have been designed for the selection of enriched uranium fuels and filling materials and the arrangement of enriched uranium and filling materials in the bundle.

[0065] While the present application has been described with reference to preferred embodiments, various modifications may be made and elements thereof may be replaced by equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An irradiation target containing a support rod for producing Mo-99 isotope in a heavy water reactor, comprising:
a plurality of fuel elements, at least one of which comprises the support rod having at least two through holes extending along an axial direction of the support rod;
an enriched uranium core provided in the through holes; and end plates provided at both ends of the fuel elements and fixedly connected to the plurality of fuel elements, wherein the enriched uranium core comprises an enriched uranium fuel having enrichment of 15.0 wt% to 20.0 wt%.

2. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to claim 1, wherein the enriched uranium fuel is UO2, UN, UC, U3S12, U metal, U-Zr alloy, or U-Al alloy, or any combination of any of them with any one or more of industrial pure zirconium, zirconium alloy, industrial pure aluminum, aluminum alloy, industrial pure molybdenum, molybdenum alloy, industrial pure niobium, niobium alloy, stainless steel, nickel alloy, and silicon carbide.

3. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to claim 1, wherein the enriched uranium core is a solid enriched uranium rod, several stacked enriched uranium pellets, or enriched uranium powder;
the enriched uranium core has a diameter of 0.5 mm to 7 mm, the support rod has an outer diameter of 10 mm to 14 mm, and a diameter of each through hole of the support rod is greater than or equal to the diameter of the enriched uranium core; and end plugs for sealing are provided at both ends of the through hole of the support rod.

4. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to claim 1, wherein the fuel element further comprises a cladding sleeved on the support rod, and additional end plugs welded on both ends of the cladding for sealing;
the enriched uranium core is a solid enriched uranium rod, several stacked enriched uranium pellets, or enriched uranium powder; and the cladding has an outer diameter of 10 mm to 14 mm, the support rod has an outer diameter of 9 mm to 13 mm, the enriched uranium core has a diameter of 0.5 mm to 7 mm, an inner diameter of the cladding is greater than or equal to the outer diameter of the support rod, and an i nner diameter of the support rod is greater than or equal to the diameter of the enriched uranium core.

5. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to any one of claims 1 to 4, wherein the support rod further has at least one through hole for filler, and a filling material is embedded in the through hole for filler to form a fi I ler.

6. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to claim 5, wherein the support rod is made of a material with a thermal neutron macroscopic absorption cross-section of less than 10 barns.

7. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to claim 6, wherein the support rod is made of any one of the following nuclear-grade materials: zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, nickel-based alloy, aluminum oxide, and beryllium oxide.

8. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to claim 4, wherein the cladding is made of a material with a thermal neutron macroscopic absorption cross-section of less than 10 barns.

9. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to claim 8, wherein the cladding is made of any one of the following nuclear-grade materials: zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, and nickel-based alloy.

10. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to claim 5, wherein the filling material is a material with a thermal neutron macroscopic absorption cross-section of greater than 1 barn.

11. The irradiation target containing the support rod for producing Mo-99 isotope in the heavy water reactor according to claim 10, wherein the filling material is a material in which a mass percentage of depleted uranium, tungsten, boron, dysprosium, gadolinium, silver, or hafnium is greater than 5%.