Neutron energy spectrum optimization method for improving isotope irradiation production conversion rate

Abstract

The invention provides a neutron spectrum optimization method for improving the isotope irradiation production conversion rate, and relates to the technical field of reactor engineering. Monte Carlo modeling is performed on an isotope target and related mechanisms; then Monte Carlo critical calculation is carried out, and initial neutron energy spectrums are obtained respectively; next, on the basis of the initial neutron energy spectrum, neutron energy spectrum sensitivity analysis is carried out on the target isotope; on the premise that the total neutron flux is kept unchanged, an ideal neutron energy spectrum is obtained; comparing the difference between the initial neutron energy spectrum and the ideal neutron energy spectrum, and arranging a neutron filter around an isotope target in the Monte Carlo model; then, the material type of the neutron filter is replaced, neutron energy spectrums under different material types are calculated through Monte Carlo criticality, and the material type capable of improving the target nuclide conversion rate is determined; and finally, based on the determined neutron filter material type, obtaining an optimized neutron energy spectrum. The conversion rate of isotope irradiation, namely the production efficiency of isotopes, can be improved.

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 is the best way to mass-produce slightly scarce nuclides and medical isotopes. Taking super plutonium nuclides as an example, they are mainly produced by irradiating Pu, Am, and Cm isotope targets in the High Flux Research Reactor. Super plutonium nuclides have the characteristics of long production chain, large loss rate, and low conversion rate. They need to undergo multi-stage (n, γ) reactions from different target nuclides to be obtained, and some nuclides in the conversion chain have large fission cross sections. There is a fission loss of nearly 99% in the entire irradiation process, resulting in an extremely low irradiation production conversion rate for the target nuclides.

[0003] Since high-throughput research reactors have complex and changeable core composition and loading layout characteristics, they pose severe challenges to achieving high-efficiency irradiation production of slightly scarce nuclides and medical isotopes. The isotope yield and its irradiation production characteristics are strongly dependent on the neutron flux and energy spectrum of the high-throughput reactor. Therefore, the core design of traditional high-throughput research reactors often fails to fully consider the impact of the neutron energy spectrum on production efficiency, 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 slowing, 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 by precise control of the neutron energy spectrum.

[0005] In addition, traditional isotope irradiation production usually adopts the Monte Carlo transport-burnup coupling method to design the isotope irradiation production plan 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, which leads to excessively high computational costs and makes it impossible to achieve efficient design of isotope irradiation production.

[0006] The Chinese patent (CN117524335A) discloses a method based on extreme burnup analysis, which can quantify the plutonium-238 production efficiency in each energy range when plutonium-238 is produced by irradiation in a reactor, thereby effectively supporting the optimization of plutonium-238 irradiation production. At the same time, based on the energy spectrum optimization technology to maximize the "total energy spectrum efficiency", the production efficiency of plutonium-238 produced by irradiation in the reactor is significantly improved, the problem of low production efficiency of traditional methods is solved, and a refined neutronics model of plutonium-238 produced by reactor irradiation is established, providing technical support for the realization of efficient plutonium-238 production; however, this method has certain limitations in local position optimization, computational cost control, and systematic impact analysis on the entire production chain, resulting in the inability to circumvent the problem of low isotope irradiation production efficiency using this method. Summary of the invention

[0007] The object of the present invention is to provide a neutron 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 implemented by 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 in the high-throughput research reactor;

[0011] S2. Monte Carlo critical calculation is performed using the critical source mode to obtain the neutron flux in multiple energy intervals of the irradiation environment where the isotope target is located, that is, the initial neutron energy spectrum;

[0012] S3. Based on the initial neutron spectrum, perform neutron spectrum sensitivity analysis on the target isotope;

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

[0014] S5. Compare the difference between the initial and ideal neutron energy spectra, 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 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;

[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 finally 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 sleeved outside the target core block, and the two are parallel to the aluminum target tube and located inside the aluminum target tube.

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

[0019] Furthermore, the tube wall of the aluminum target tube is provided with an interlayer, and 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. Taking the initial neutron energy spectrum as input, the neutron energy interval value analysis is carried out using the fast ignition consumption calculation to obtain the target super-plutonium isotope yield after the isotope target is irradiated for 100 equivalent full-power days;

[0027] S33. The neutron flux of each energy interval is adjusted in sequence, and the neutron flux ratio of other energy intervals is maintained unchanged during the adjustment, using the formula:

[0028]

[0029] The conversion rate of the target isotope in each energy interval is calculated, and the neutron energy interval in which the target nucleus has a positive or negative correlation effect on 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 solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0034] The present invention provides a neutron spectrum optimization method for improving the isotope irradiation production conversion rate. The neutron filter can selectively absorb or slow down neutrons within a specific energy range, thereby changing the neutron spectrum in a local area. Further, 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 the traditional method, the present method adopts 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 cycles of irradiation 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 drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 A schematic diagram of a method flow chart 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] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 here 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 claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are 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, further definition and explanation thereof is not required 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 used. 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] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[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, cores and isotope targets 1 in the high-throughput research reactor;

[0049] Among them, the full-core Monte Carlo modeling of the core at different burnup times is completed based on information such as balanced cycle core loading, fuel burnup distribution and critical rod position; based on this full-core Monte Carlo model, the isotope target 1 is Monte Carlo modeling is carried out, and the isotope target 1 is placed at different positions in the core active area;

[0050] In addition, the High Flux Research Reactor provides an irradiation environment for isotope production. The height of the core active zone is 100 cm. The fuel uses low-enriched uranium multi-layer sleeve-type fuel assemblies, water is used as a moderator, and beryllium is used as a reflector. The control of fuel reactivity is mainly achieved through control rods, which are composed of an absorber (Ag-I n-Cd), a transition section (stainless steel) and a follower (Be). For the geometric and material modeling of different components in the High Flux Research Reactor, such as fuel assemblies, burnable poisons, beryllium blocks, aluminum blocks, stainless steel blocks, control rods, etc., it is necessary to refer to information such as balanced cycle core loading, fuel consumption distribution, and critical rod positions, and fill these components into the corresponding positions of the core according to a repeated geometric structure to complete the overall modeling of the core.

[0051] Taking the central channel of the fuel element as an example, the position of the fuel element closest to the center of the core is determined, and the center of the multilayer tube fuel assembly has an irradiation space with a diameter of 1.4 cm, which can be used to place the isotope target 1; and 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 core block 13, wherein the aluminum cladding 12 is sleeved outside the target core block 13, and the two are parallel to the aluminum target tube 11 and located inside the aluminum target tube 11. In addition, the radius of the target core block 13 is set to 0.24765 cm. A typical super-plutonium isotope production target is composed of mixed curium, plutonium and americium isotopes. The radius of the aluminum alloy cladding is 0.31623 cm, the radius of the aluminum alloy target tube 11 is 0.47625 cm, and the aluminum alloy material used is 6061 aluminum alloy.

[0053] S2. Monte Carlo critical calculation is performed using a critical source mode to obtain neutron fluxes in multiple energy intervals of the irradiation environment where the isotope target 1 is located, that is, the initial neutron energy spectrum;

[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 100000*1000=100000000;

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

[0058] Table 1 Energy interval structure of neutron spectrum of group 44 and calculation results of neutron spectrum

[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, and then the neutron flux of the target core in 44 energy intervals obtained by S2, that is, the initial neutron energy spectrum, is used to calculate the ignition consumption, so as to obtain the yield and conversion rate of the target isotope; and the neutron energy interval value analysis is carried out, and the neutron flux of each interval in the 44 energy intervals is perturbed in turn, while the other energy intervals remain unchanged, which is used to analyze the change of the target nuclide yield with the irradiation time caused by the change of the flux in a single energy interval, so as to study the neutron energy interval and sensitivity of the target nuclide conversion rate that is positively / negatively correlated / negatively correlated, and determine the neutron energy range that is conducive to improving the conversion rate;

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

[0064] At present, the target nuclide conversion rate of the initial neutron spectrum is 2.63%, and the target nuclide conversion rate after adjustment can reach up to 3.35%. Based on the results of the neutron spectrum sensitivity analysis, the initial neutron spectrum is adjusted while keeping the total neutron flux unchanged. By comparing the calculation results of different neutron spectra after adjustment, the optimized neutron spectrum, i.e., the ideal neutron spectrum, can be obtained as shown in Table 3. Using the optimized ideal neutron spectrum, the target super-plutonium isotope yield is increased by 100.36%, and the target super-plutonium isotope conversion rate is 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] Particularly, the tube wall of the aluminum target tube 11 is provided with an interlayer, and a neutron filter 2 is arranged in the interlayer, and the neutron filter 2 correspondingly surrounds the target core block 13 .

[0070] 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;

[0071] S7. Based on the material type of the neutron filter 2 determined in S7, the corresponding neutron energy spectrum, as well as the yield and conversion rate of the target isotope are calculated to finally obtain an optimized neutron energy spectrum;

[0072] For S5-S7, based on the initial neutron energy spectrum and the ideal neutron energy spectrum, the energy interval that is positively or negatively correlated with the target nuclide conversion rate can be analyzed, so that different neutron moderation or absorption materials are used as candidate neutron filter 2 materials, and then the neutron flux of the energy group that is positively correlated with the target nuclide conversion rate is increased through the energy spectrum, and the neutron flux of the energy group that is negatively correlated with the target nuclide conversion rate is suppressed. The optimized neutron energy spectrum is constructed using different neutron filter 2 materials. In particular, 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;

[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-sections of different moderator materials are considered. Different neutron energy spectra are obtained through Monte Carlo calculations, and the yield is calculated using the ignition consumption calculation program. As shown in Table 4, the target super plutonium isotope yield improvement and conversion rate calculation results using different neutron filter 2 materials (parts) are listed. After modifying the neutron filter layer material, the target isotope yield and conversion rate are 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 materials and their daughter products (mainly transuranic nuclides Pu, Am, Cm, Cf, etc.) are in a dynamic process of being produced and lost, so the production of the target isotope can be obtained by using this formula;

[0083] S32. Using the initial neutron energy spectrum as input, the ignition consumption calculation program is used to carry out neutron energy interval value analysis to obtain the yield of the target super-plutonium isotope after the isotope target 1 is irradiated for 100 equivalent full-power days;

[0084] S33. The neutron flux of each energy interval is adjusted in sequence, and the neutron flux ratio of other energy intervals is maintained 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 effect on the conversion rate of the target isotope;

[0087] The changes in the target isotope yield in each energy interval 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 effect on the target isotope conversion rate, where the energy ranges in which the target isotope yield is improved are: 17, 18, 20, 22, and 25, and the remaining energy ranges all lead to a decrease in the calculated yield of the target isotope;

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

[0093] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A neutron spectrum optimization method for improving isotope irradiation production conversion rate, characterized in that: include: S1. Monte Carlo modeling of various components, cores and isotope targets (1) in a high-throughput research reactor; S2. Monte Carlo critical calculation is performed using a critical source mode to obtain 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, the ideal neutron spectrum is calculated based on the results of the initial neutron spectrum and the neutron spectrum sensitivity analysis; 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; 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 to finally obtain an optimized neutron energy spectrum.

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 two are parallel to the aluminum target tube (11) and are 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: The number of energy intervals is 44.

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 the isotope target (1) is irradiated for 100 equivalent full-power days; S33. The neutron flux of each energy interval is adjusted in sequence, and the neutron flux ratio of other energy intervals is maintained unchanged during the adjustment, using the formula: The conversion rate of the target isotope in each energy interval is calculated, and the neutron energy interval in which the target nucleus has a positive or negative correlation effect on 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.

Images