A neutron spectrum optimization method for improving isotope irradiation production conversion rate

Abstract

The present invention provides a neutron spectrum optimization method for improving the isotope irradiation production conversion rate, which relates to the field of reactor engineering technology. The method comprises the following steps: performing Monte Carlo modeling on an isotope target and related mechanisms; then performing Monte Carlo critical calculations to obtain initial neutron spectra; then performing neutron spectrum sensitivity analysis on the target isotope based on the initial neutron spectrum; then obtaining an ideal neutron spectrum while keeping the total neutron flux unchanged; then comparing the difference between the initial and ideal neutron spectra, and arranging a neutron filter around the isotope target in the Monte Carlo model; then, by changing the material type of the neutron filter and performing Monte Carlo critical calculations on the neutron spectra under different material types, determining a material type that can achieve an improved target nuclide conversion rate; and finally, obtaining an optimized neutron spectrum based on the determined neutron filter material type. The method can improve the isotope irradiation conversion rate, that is, the isotope production efficiency.

Description

Technical Field

[0001] The present invention relates to the field of reactor engineering technology, and in particular to a neutron energy spectrum optimization method for improving isotope irradiation production conversion efficiency. Background Art

[0002] Due to its high neutron flux density, the High Flux Research Reactor (HFRR) is the best way to mass-produce slightly scarce nuclides and medical isotopes. Taking transplutonium nuclides as an example, they are mainly produced in the HFRR by irradiating Pu, Am, and Cm isotope targets. However, transplutonium nuclides have the characteristics of a long production chain, a large loss rate, and a low conversion rate. Starting from different target nuclides, multiple (n, γ) reactions are required to obtain them. In addition, some nuclides in the conversion chain have a large fission cross-section. During the entire irradiation process, there is a fission loss of nearly 99%, resulting in an extremely low conversion rate of the target nuclide irradiation production.

[0003] Due to the complex and variable core composition and loading layout characteristics of high-flux research reactors, achieving high-efficiency irradiation production of slightly scarce nuclides and medical isotopes poses a severe challenge. The isotope yield and its irradiation production characteristics are strongly dependent on the neutron flux and energy spectrum of the high-flux reactor. Therefore, the impact of the neutron energy spectrum on production efficiency is often not fully considered in the core design of traditional high-flux research reactors, resulting in unsatisfactory irradiation production conversion rate of the target isotope.

[0004] In addition, the irradiation production of different isotopes requires different neutron energy spectrum environments. Since the reaction cross-sections of some nuclides in the production chain are strongly dependent on the incident neutron energy, the conversion rate of the target isotope can be significantly improved by optimizing the neutron energy spectrum in the target irradiation environment. By arranging neutron moderation, shielding, and filtering materials, the resonant self-screening effect of the target can be fully utilized to obtain a conversion rate higher than the neutron energy spectrum before optimization, and the production efficiency of the target isotope can be improved through precise control of the neutron energy spectrum.

[0005] In addition, traditional isotope irradiation production usually uses the Monte Carlo transport-burnup coupling method to design isotope irradiation production plans and evaluate the isotope irradiation production efficiency during the irradiation production process. However, the production of some isotopes often requires several or even dozens of irradiation cycles in the reactor, resulting in excessive computational costs and the inability to achieve efficient design of isotope irradiation production.

[0006] A Chinese patent (CN117524335A) discloses a method based on extreme burnup analysis that quantifies the plutonium-238 production efficiency within various energy ranges during plutonium-238 production in reactors. This method effectively supports the optimization of plutonium-238 irradiation production. Furthermore, it maximizes the "total energy spectrum efficiency" based on energy spectrum optimization technology, significantly improving the efficiency of plutonium-238 production in reactors. This addresses the low production efficiency of traditional methods and establishes a refined neutronics model for plutonium-238 production by reactor irradiation, providing technical support for achieving efficient plutonium-238 production. However, this method has limitations in terms of local location optimization, computational cost control, and analysis of systemic impacts across the entire production chain, resulting in an inability to circumvent the low efficiency of isotope irradiation production. Summary of the Invention

[0007] The object of the present invention is to provide a neutron energy spectrum optimization method for improving the isotope irradiation production conversion rate, which can improve the isotope irradiation conversion rate, that is, the isotope production efficiency.

[0008] The embodiments of the present invention are achieved through the following technical solutions:

[0009] A neutron spectrum optimization method for improving isotope irradiation production conversion rate, comprising:

[0010] S1. Monte Carlo modeling of various components, cores, and isotope targets within the high-throughput research reactor;

[0011] S2. Perform Monte Carlo criticality calculations using the critical source model to obtain the neutron fluxes in multiple energy intervals of the irradiation environment where the isotope target is located, i.e., the initial neutron energy spectrum;

[0012] S3. Perform neutron spectrum sensitivity analysis on the target isotope based on the initial neutron spectrum;

[0013] S4. Under the premise of keeping the total neutron flux unchanged, calculate the ideal neutron spectrum based on the initial neutron spectrum and the results of the neutron spectrum sensitivity analysis;

[0014] S5. Compare the initial neutron spectrum with the ideal one and set a neutron filter around the isotope target in the Monte Carlo model;

[0015] S6. By changing the material type of the neutron filter and then calculating the neutron energy spectrum under different material types using Monte Carlo criticality, determine the material type that can achieve the target nuclide conversion rate improvement;

[0016] S7. Based on the material type of the neutron filter determined in S6, the corresponding neutron energy spectrum, as well as the yield and conversion rate of the target isotope are calculated to ultimately obtain an optimized neutron energy spectrum.

[0017] Furthermore, the isotope target in S1 includes an aluminum target tube, an aluminum cladding and a target core block, wherein the aluminum cladding is arranged outside the target core block, and the aluminum cladding and the target core block are parallel to and located inside the aluminum target tube.

[0018] Furthermore, the material of the aluminum target tube is 6061 aluminum alloy.

[0019] Furthermore, the tube wall of the aluminum target tube is provided with an interlayer, a neutron filter is arranged in the interlayer, and the neutron filter correspondingly surrounds the target core block.

[0020] Furthermore, the isotope target is composed of mixed curium, plutonium and americium isotopes.

[0021] Furthermore, the number of energy intervals is 44.

[0022] Furthermore, the step of neutron spectrum sensitivity analysis includes:

[0023] S31. Use the formula:

[0024]

[0025] Calculate isotope N i The nuclear density of

[0026] S32. Using the initial neutron energy spectrum as input, perform a neutron energy range value analysis using a fast ignition consumption calculation to determine the target super-plutonium isotope yield after irradiating the isotope target for 100 days at equivalent full power.

[0027] S33. Adjust the neutron flux of each energy range in sequence, and maintain the neutron flux ratio of other energy ranges unchanged during the adjustment, using the formula:

[0028]

[0029] The conversion rate of the target isotope in each energy range is calculated, and the neutron energy range in which the target nucleus has a positive or negative correlation with the conversion rate of the target isotope is determined.

[0030] Furthermore, the amplitude of sequentially adjusting the neutron flux of each energy interval in S33 is ±1%.

[0031] Furthermore, the initial material type of the neutron filter is aluminum.

[0032] Furthermore, the replaceable material type of the neutron filter is set to beryllium, beryllium oxide, zirconium hydride, heavy water, graphite high-density polyethylene, light water or yttrium hydride.

[0033] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0034] The present invention provides a neutron spectrum optimization method for improving the conversion rate of isotope irradiation production. The method selectively absorbs or slows down neutrons within a specific energy range through a neutron filter, thereby changing the neutron spectrum in a local area. Furthermore, by adjusting the material type and arrangement of the neutron filter, the yield and conversion rate of the target isotope can be significantly improved.

[0035] By dividing the neutron energy into multiple intervals, the neutron flux in each energy interval and its impact on the target isotope yield and conversion rate can be analyzed more finely. At the same time, based on the sensitivity analysis of different energy intervals, the neutron flux ratio of these intervals can be adjusted in a targeted manner to construct an ideal neutron energy spectrum; this can significantly improve the conversion efficiency of the target isotope and reduce adverse effects such as unnecessary fission losses.

[0036] In addition, compared with traditional methods, this method uses a fast ignition consumption calculation program to determine the target isotope yield and conversion rate, which helps to reduce the computational burden, especially when multiple irradiation cycles are required, and improves the design efficiency of the neutron energy spectrum optimization scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 A schematic diagram of the method flow provided in Example 1 of the present invention;

[0039] Figure 2 Schematic diagram of the structure of the isotope target.

[0040] In the figure: 1. Isotope target; 11. Aluminum target tube; 12. Aluminum cladding; 13. Target core block; 2. Neutron filter. DETAILED DESCRIPTION

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0042] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0043] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0044] In the description of the present invention, it should be noted that if the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the application is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0045] It should also be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific contexts.

[0046] Example 1

[0047] A neutron spectrum optimization method for improving isotope irradiation production conversion rate, comprising:

[0048] S1. Monte Carlo modeling of various components, the core, and isotope targets within the high-throughput research reactor;

[0049] The full-core Monte Carlo modeling of the core at different burnup times was completed based on information such as balanced cycle core loading, fuel burnup distribution, and critical rod positions. Based on this full-core Monte Carlo model, the isotope target 1 was Monte Carlo modeled and placed at different locations in the core active area.

[0050] In addition, the High Flux Research Reactor (HTR) provides an irradiation environment for isotope production. Its core active region is 100 cm high and uses low-enriched uranium multi-layered jacketed fuel assemblies as fuel. Water is used as the moderator and beryllium as the reflector. Fuel reactivity is primarily controlled by control rods, which consist of an absorber (Ag-In-Cd), a transition section (stainless steel), and a follower (Be). Geometric and material modeling of various components within the HTR, such as fuel assemblies, burnable poisons, beryllium blocks, aluminum blocks, stainless steel blocks, and control rods, requires reference to information such as balanced cycle core loading, fuel burnup distribution, and critical rod positions. These components are then placed in the corresponding positions of the core according to a repeating geometric structure to complete the overall core modeling.

[0051] Taking the central channel of the fuel element as an example, the position of the fuel element closest to the core center is determined. The center of the multi-layered sheathed fuel assembly has an irradiation space with a diameter of 1.4 cm, which can be used to place the isotope target 1. The modeling process of the isotope target 1 is as follows:

[0052] As attached Figure 2 As shown, the target is designed in the form of a concentric cylinder, including an aluminum target tube 11, an aluminum cladding 12 and a target pellet 13, wherein the aluminum cladding 12 is sleeved outside the target pellet 13, and the aluminum cladding 12 is parallel to and located inside the aluminum target tube 11. In addition, the radius of the target pellet 13 is set to 0.24765 cm. A typical trans-plutonium isotope production target is composed of mixed curium, plutonium and americium isotopes. The radius of the aluminum alloy cladding is 0.31623 cm, and the radius of the aluminum alloy target tube 11 is 0.47625 cm. The aluminum alloy material used is 6061 aluminum alloy.

[0053] S2. Performing Monte Carlo criticality calculations using a critical source mode to obtain neutron fluxes in multiple energy intervals of the irradiation environment where the isotope target 1 is located, i.e., initial neutron energy spectra;

[0054] The calculation principle is as follows: S21. In the Monte Carlo simulation, 100,000 neutron particles are generated in each generation for tracking and calculation;

[0055] S22. A total of 1100 generations were calculated, but the first 100 generations were discarded to ensure data stability.

[0056] S23. Therefore, the total number of particles actually used for statistical analysis is 100,000*1000=100,000,000;

[0057] S24. Through these calculations, the neutron energy spectra of 44 energy intervals at the target core position were obtained. The calculation results are shown in Table 1.

[0058] Table 1 44-group neutron spectrum energy interval structure and neutron spectrum calculation results

[0059]

[0060]

[0061] S3. Based on the initial neutron spectrum, perform neutron spectrum sensitivity analysis on the target isotope;

[0062] First, the initial nuclear density of the target core and the target nucleus is set to be consistent. Then, based on the neutron flux of the target core in 44 energy intervals obtained by S2, that is, the initial neutron energy spectrum, an ignition consumption calculation program is performed to obtain the yield and conversion rate of the target isotope; and a neutron energy interval value analysis is carried out. The neutron flux in each of the 44 energy intervals is perturbed in turn, while the other energy intervals remain unchanged. This is used to analyze the change in the target nuclide yield with irradiation time caused by the flux change in a single energy interval, thereby studying the neutron energy range and sensitivity of the target nuclide that is positively / negatively correlated with the conversion rate of the target nuclide, and determining the neutron energy range that is conducive to improving the conversion rate;

[0063] S4. Under the premise of keeping the total neutron flux unchanged, calculate the ideal neutron spectrum based on the initial neutron spectrum and the results of the neutron spectrum sensitivity analysis;

[0064] Currently, the target nuclide conversion rate for the initial neutron spectrum is 2.63%. After adjustment, the target nuclide conversion rate can reach a maximum of 3.35%. Based on the results of the neutron spectrum sensitivity analysis, the initial neutron spectrum was adjusted while maintaining the total neutron flux unchanged. Comparing the calculated results of different neutron spectra after adjustment, the optimized neutron spectrum (i.e., the ideal neutron spectrum) was obtained as shown in Table 3. Using the optimized ideal neutron spectrum, the target trans-plutonium isotope yield was calculated to increase by 100.36%, and the target trans-plutonium isotope conversion rate was increased by 4.34%.

[0065] Table 3 Optimized ideal neutron energy spectrum

[0066]

[0067]

[0068] S5. Compare the difference between the initial and ideal neutron energy spectra, and set a neutron filter 2 around the isotope target 1 in the Monte Carlo model;

[0069] In particular, the tube wall of the aluminum target tube 11 is provided with an interlayer, and a neutron filter 2 is arranged in the interlayer. The neutron filter 2 correspondingly surrounds the target core block 13 .

[0070] S6. By changing the material type of neutron filter 2, and then calculating the neutron energy spectrum under different material types by Monte Carlo criticality, determine the material type that can achieve the target nuclide conversion rate improvement;

[0071] S7. Based on the material type of the neutron filter 2 determined in S7, calculating the corresponding neutron energy spectrum, as well as the yield and conversion rate of the target isotope, ultimately obtaining an optimized neutron energy spectrum;

[0072] For S5-S7, based on the initial neutron energy spectrum and the ideal neutron energy spectrum, it is possible to analyze energy intervals that are positively or negatively correlated with the target nuclide transmutation rate, thereby using different neutron moderators or absorbers as candidate neutron filter 2 materials. Then, the energy spectrum is used to increase the neutron flux of energy groups that are positively correlated with the target nuclide transmutation rate, while suppressing the neutron flux of energy groups that are negatively correlated with the target nuclide transmutation rate. An optimized neutron energy spectrum is constructed using different neutron filter 2 materials. In particular, the replaceable material types of the neutron filter 2 are set to beryllium, beryllium oxide, zirconium hydride, heavy water, graphite high-density polyethylene, light water, or yttrium hydride.

[0073] The initial material of the initial neutron filter layer outside the isotope target 1 is aluminum, and the thickness of the filter layer is 0.3 cm. At this time, the target super plutonium isotope conversion rate is 2.61%. The material type of the neutron filter 2 in the Monte Carlo modeling is modified, and the thermalization cross-section of different moderator materials is considered. Different neutron energy spectra are obtained through Monte Carlo calculation, and the yield is calculated using the ignition consumption calculation program. Table 4 lists the target super plutonium isotope yield improvement and conversion rate calculation results using different neutron filter 2 materials (parts). After modifying the neutron filter layer material, the target isotope yield and conversion rate are both improved to a certain extent, among which the yield improvement effect of yttrium hydride is more obvious.

[0074] Table 4 Calculation results of target excess plutonium isotopes after adding different neutron filter materials

[0075]

[0076] Example 2

[0077] Based on S3 in Example 1, the specific steps of the neutron spectrum sensitivity analysis include:

[0078] S31. Use the formula:

[0079]

[0080] Calculate isotope N i The nuclear density of

[0081] Among them, when the target is irradiated, individual atoms of these isotopes can 1) capture neutrons and transform into heavier isotopes, 2) capture neutrons and fission, 3) beta decay and transform into higher elements of the same mass, 4) alpha decay into lighter elements of lower mass;

[0082] During the entire transmutation process, the target material and its daughter products (mainly transuranic nuclides Pu, Am, Cm, Cf, etc.) are in a dynamic process of both production and loss. Therefore, this formula can be used to obtain the production of the target isotope.

[0083] S32. Using the initial neutron energy spectrum as input, perform a neutron energy range value analysis using an ignition consumption calculation program to determine the yield of the target trans-plutonium isotope after irradiating the isotope target 1 for 100 equivalent full-power days;

[0084] S33. Adjust the neutron flux of each energy range in sequence, and maintain the neutron flux ratio of other energy ranges unchanged during the adjustment, using the formula:

[0085]

[0086] Calculate the conversion rate of the target isotope in each energy range and determine the neutron energy range in which the target nucleus has a positive or negative correlation with the conversion rate of the target isotope;

[0087] The changes in target isotope yields in each energy range are shown in Table 2:

[0088] Table 2 Calculation results of target excess plutonium isotope yield after neutron spectrum perturbation

[0089]

[0090]

[0091] According to the results in Table 2, it is possible to determine the neutron energy ranges in which the target nucleus has a positive or negative correlation with the target isotope conversion rate. The energy ranges in which the target isotope yield is improved are: 17, 18, 20, 22, and 25, while the remaining energy ranges all lead to a decrease in the target isotope calculated yield.

[0092] In particular, the amplitude of sequentially adjusting the neutron flux of each energy interval in S33 is ±1%.

[0093] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A neutron spectrum optimization method for improving isotope irradiation production conversion efficiency, characterized by: include: S1. Monte Carlo modeling of various components, cores, and isotope targets within the high-throughput research reactor (1); S2. Monte Carlo criticality calculation is performed using a critical source mode to obtain the neutron fluxes in multiple energy intervals of the irradiation environment where the isotope target (1) is located, that is, the initial neutron energy spectrum; S3. Based on the initial neutron spectrum, perform neutron spectrum sensitivity analysis on the target isotope; S4. Under the premise of keeping the total neutron flux unchanged, calculate the ideal neutron spectrum based on the initial neutron spectrum and the results of the neutron spectrum sensitivity analysis; S5. Comparing the difference between the initial and ideal neutron energy spectra, a neutron filter (2) is set around the isotope target (1) in the Monte Carlo model; S6. By changing the material type of the neutron filter (2), and then calculating the neutron energy spectrum under different material types by Monte Carlo criticality, determine the material type that can achieve the target nuclide conversion rate improvement; S7. Based on the material type of the neutron filter (2) determined in S6, the corresponding neutron energy spectrum, as well as the yield and conversion rate of the target isotope are calculated, and finally an optimized neutron energy spectrum is obtained.

2. The neutron spectrum optimization method for improving isotope irradiation production conversion efficiency according to claim 1, characterized in that: The isotope target (1) in S1 comprises an aluminum target tube (11), an aluminum cladding (12), and a target core block (13), wherein the aluminum cladding (12) is sleeved outside the target core block (13), and the aluminum cladding (12) is parallel to the aluminum target tube (11) and is located inside the aluminum target tube (11).

3. The neutron spectrum optimization method for improving isotope irradiation production conversion efficiency according to claim 2, characterized in that: The aluminum target tube (11) is made of 6061 aluminum alloy.

4. The neutron spectrum optimization method for improving isotope irradiation production conversion efficiency according to claim 2, characterized in that: The tube wall of the aluminum target tube (11) is provided with an interlayer, a neutron filter (2) is arranged in the interlayer, and the neutron filter (2) corresponds to surrounding the target core block (13).

5. The neutron spectrum optimization method for improving isotope irradiation production conversion efficiency according to claim 2, characterized in that: The isotope target (1) is composed of mixed curium, plutonium and americium isotopes.

6. The neutron spectrum optimization method for improving isotope irradiation production conversion efficiency according to claim 1, characterized in that: There are 44 energy intervals.

7. The neutron spectrum optimization method for improving isotope irradiation production conversion efficiency according to claim 1, characterized in that: The steps of neutron spectrum sensitivity analysis include: S31. Use the formula: Calculate isotope N i The nuclear density of S32. Using the initial neutron energy spectrum as input, a neutron energy group value analysis is performed using a fast ignition consumption calculation to obtain the target super-plutonium isotope yield after irradiating the isotope target (1) for 100 days at equivalent full power; S33. Adjust the neutron flux of each energy range in sequence, and maintain the neutron flux ratio of other energy ranges unchanged during the adjustment, using the formula: The conversion rate of the target isotope in each energy range is calculated, and the neutron energy range in which the target nucleus has a positive or negative correlation with the conversion rate of the target isotope is determined.

8. The neutron spectrum optimization method for improving isotope irradiation production conversion efficiency according to claim 7, characterized in that: The amplitude of sequentially adjusting the neutron flux of each energy interval in S33 is ±1%.

9. The neutron spectrum optimization method for improving isotope irradiation production conversion efficiency according to claim 1, characterized in that: The initial material type of the neutron filter (2) is aluminum.

10. The neutron spectrum optimization method for improving isotope irradiation production conversion efficiency according to claim 1, characterized in that: The replaceable material type of the neutron filter (2) is set to beryllium, beryllium oxide, zirconium hydride, heavy water, graphite high-density polyethylene, light water or yttrium hydride.

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