Neutron unidirectional flow method for producing super-plutonium isotopes based on ultra-high flux fast neutron reactor irradiation

Abstract

The present invention relates to a neutron unidirectional flow method for producing super-plutonium isotopes based on irradiation of ultra-high flux fast neutron reactors. The control material is arranged between the fuel zone and the moderator zone. The fast neutrons generated by nuclear fuel fission can pass through the control material and enter the moderator zone and the target zone, thereby being moderated into thermal neutrons for irradiation production. The thermal neutrons in the target zone are absorbed after contacting the control material and cannot reach the fuel zone, and will not cause fission. Compared with the prior art, the method of the present invention solves the problem of sudden increase in fission power in the fuel zone around the irradiation channel for producing super-plutonium isotopes based on irradiation of ultra-high flux fast neutron reactors, reduces the fission power and temperature of the zone, realizes the unidirectional flow of thermal neutrons, and improves the production capacity, safety and economy of producing super-plutonium isotopes based on irradiation of ultra-high flux fast neutron reactors.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear reactor production control, in particular to a neutron unidirectional flow method for producing super-plutonium isotopes based on ultra-high flux fast neutron reactor irradiation. Background Art

[0002] Ultra-high flux fast neutron reactors can slow down the consumption of nuclear fuel while having a high neutron flux environment, thereby improving the economic efficiency of irradiation production of super-plutonium isotopes. However, the irradiation production of super-plutonium isotopes requires a thermal neutron environment. Therefore, a neutron unidirectional flow technology is urgently needed to construct a local thermal neutron environment in the ultra-high flux fast neutron reactor, which can prevent thermal neutrons from flowing into the core fuel area while achieving a high-flux thermal neutron environment in the irradiation channel. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation, which can prevent thermal neutrons from flowing into the core fuel zone while realizing a high flux thermal neutron environment in the irradiation channel, thereby providing technical support for the irradiation production of super plutonium isotopes based on ultra-high flux fast neutron reactor. The present invention aims at the problem that when irradiating super plutonium isotopes in an ultra-high flux fast neutron reactor, in order to increase the thermal neutron flux, a moderator is arranged around the irradiation channel to generate a large number of thermal neutrons, thereby causing a sudden increase in the fission power of the fuel zone around the irradiation channel, and proposes a neutron unidirectional flow technology. The present invention realizes the unidirectional flow of thermal neutrons in the ultra-high flux fast neutron reactor, and arranges a control material between the irradiation channel and the fuel zone, so that the fast neutrons in the fuel zone can flow to the irradiation channel, and the thermal neutrons in the irradiation channel cannot flow to the fuel zone. This method realizes the unidirectional flow of neutrons, significantly reduces the fission power of the fuel zone, and enables the ultra-high flux fast neutron reactor to have both irradiation production capacity, safety and economy.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] The purpose of the present invention is to provide a neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation, wherein a moderator and a control material are arranged around the irradiation channel of the ultra-high flux fast neutron reactor, and the control material is screened out by comparing and analyzing the fission power of the initial plan of the ultra-high flux fast neutron reactor and the fission power before and after the control material is arranged, so as to reduce the fission power of the fuel zone and realize the unidirectional flow of neutrons.

[0006] Furthermore, the super-plutonium isotope is selected from but not limited to californium-252. Super-plutonium isotopes refer to nuclides with element numbers greater than or equal to plutonium. Pu-238, curium-244, etc. can also be selected.

[0007] Furthermore, the moderator is selected from but not limited to zirconium hydride.

[0008] Furthermore, the control material refers to a material whose reaction cross section in the thermal energy zone is much larger than that in the fast energy zone.

[0009] Furthermore, the control material is preferably cadmium-113 or gadolinium-157.

[0010] Furthermore, the initial plan of the ultra-high flux fast neutron reactor refers to an initial reactor plan without the arrangement of moderators and control materials.

[0011] Furthermore, the fission power before the control material is arranged refers to the fission power distribution of the fuel area around the irradiation channel after only the moderator is arranged.

[0012] Furthermore, the fission power after the control material is arranged refers to: after the moderator and the control material are arranged at the same time, the fission power distribution of the fuel area around the irradiation channel.

[0013] Furthermore, the arrangement means that the irradiation channel is located in the reactor fuel zone, the target is placed in the center of the irradiation channel, the moderator surrounds the target, and the control material surrounds the moderator.

[0014] Furthermore, the arrangement from inside to outside is a target, a moderator, a control material, and a fuel area. Furthermore, the method specifically comprises the following steps:

[0015] Step 1: Model the initial scheme of the ultra-high flux fast neutron reactor (hereinafter referred to as the initial scheme), perform criticality calculations, and obtain the full-stack fission power distribution of the initial scheme;

[0016] Step 2: construct an irradiation channel (referred to as the production plan) at the central assembly of the ultra-high flux fast neutron reactor, arrange the moderator and target, perform criticality calculations, and obtain the full-stack fission power distribution of the production plan;

[0017] Step 3: Compare the fission power distribution of the fuel area around the irradiation channel of the initial scheme and the production scheme, and select the control material in the nuclear database according to the difference in fission power distribution between the two schemes;

[0018] Step 4: Arrange control materials (referred to as optimization scheme) in the irradiation channel, and screen the control materials and arrangement schemes by comparing the fission power distribution of the production scheme and the optimization scheme to obtain the best optimization scheme.

[0019] Furthermore, after step 4, execute:

[0020] Step 5: By performing neutron physics-thermal coupling calculations on the reactor models of the initial scheme, production scheme, and optimized scheme, the fission power distribution of the fuel area around the irradiation channel is obtained to verify the technical effect of the neutron unidirectional flow method.

[0021] Furthermore, the method arranges the control material between the fuel zone and the moderating zone, and the fast neutrons generated by the fission of the nuclear fuel can pass through the control material and enter the moderating zone and the target zone, thereby being moderated into thermal neutrons for irradiation production. The thermal neutrons in the target zone are absorbed after contacting the control material and cannot reach the fuel zone, and will not induce fission.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The unidirectional neutron flow method for producing super-plutonium isotopes based on irradiation in an ultra-high flux fast neutron reactor provided by the technical solution realizes the unidirectional flow of thermal neutrons in the ultra-high flux fast neutron reactor. By arranging control materials between the irradiation channel and the fuel zone, the fast neutrons in the fuel zone can flow to the irradiation channel, and the thermal neutrons in the irradiation channel cannot flow to the fuel zone.

[0024] 2) The technical solution provides a unidirectional neutron flow method for producing super-plutonium isotopes based on ultra-high flux fast neutron reactor irradiation, which solves the problem of sudden increase in fission power in the fuel area around the irradiation channel when producing super-plutonium isotopes based on ultra-high flux fast neutron reactor irradiation, reduces the fission power and temperature in this area, realizes the unidirectional flow of thermal neutrons, and improves the production capacity, safety and economy of producing super-plutonium isotopes based on ultra-high flux fast neutron reactor irradiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of an embodiment of the present invention;

[0026] Figure 2 It is a simplified XY cross-sectional diagram of an ultra-high flux fast neutron reactor model according to an embodiment of the present invention;

[0027] Figure 3 It is a simplified XZ cross-section diagram of an ultra-high flux fast neutron reactor model according to an embodiment of the present invention;

[0028] Figure 4 A schematic diagram of the full-stack fission power distribution of an initial solution of an ultra-high flux fast neutron reactor according to an embodiment of the present invention;

[0029] Figure 5 A schematic diagram of the full-stack fission power distribution of an ultra-high flux fast neutron reactor production solution according to an embodiment of the present invention;

[0030] Figure 6A schematic diagram of the whole-stack fission power distribution of an ultra-high flux fast neutron reactor optimization solution according to an embodiment of the present invention;

[0031] Figure 7 This is a comparison diagram of the fission power of fuel rods in the initial scheme and the production scheme of the ultra-high flux fast neutron reactor according to an embodiment of the present invention;

[0032] Figure 8 A graph showing the variation of the reaction cross section of cadmium-113 with energy according to an embodiment of the present invention;

[0033] Fig. 9 This is a graph showing the variation of the reaction cross section of gadolinium-152 with energy according to an embodiment of the present invention;

[0034] Fig.10 A schematic diagram of the fuel assembly temperature of an initial solution of an ultra-high flux fast neutron reactor according to an embodiment of the present invention;

[0035] Fig.11 A schematic diagram of the fuel assembly temperature of an ultra-high flux fast neutron reactor production solution according to an embodiment of the present invention;

[0036] Fig.12 This is a schematic diagram of the fuel assembly temperature of the ultra-high flux fast neutron reactor optimization solution according to an embodiment of the present invention.

[0037] In the figure, a=298.14cm, b=58.14cm, c=50cm, d=210cm. DETAILED DESCRIPTION

[0038] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The features such as component models, material names, connection structures, control methods, etc. that are not clearly described in this technical solution are all regarded as common technical features disclosed in the prior art.

[0039] Example

[0040] This embodiment Figure 2 , 3 The ultra-high flux fast neutron reactor shown in the figure provides a production environment for the production of the typical super-plutonium isotope californium-252. The reactor (including the fuel zone and reflector and other structures) is in the shape of a cylinder with a diameter of 298.14 cm and a height of 210 cm, wherein the core active area (including the target, irradiation channel, moderator, control material, fuel zone and other areas) has a diameter of 58.14 cm and a height of 50 cm. The outer periphery of the active area is a reflector, and the radial and axial lengths of the reflector are 120 cm and 80 cm respectively.

[0041] like Figure 1 As shown, this embodiment specifically includes:

[0042] Step 1: Conduct geometric modeling and material modeling of the ultra-high flux fast neutron reactor, perform criticality calculations, and obtain the fission power distribution of the 9919 fuel rods in the entire stack (the fission power distribution of the entire stack in the initial scheme).

[0043] Step 2: Construct a production plan model of the ultra-high flux fast neutron reactor, re-perform geometric modeling and material modeling, perform critical calculations, and obtain the fission power of the central irradiation channel and the fission power distribution of the 9828 fuel rods in the whole stack (the fission power distribution of the whole stack of the production plan).

[0044] Step 3: By comparing the fission power distribution diagrams of the entire reactor between the initial plan and the production plan, it is determined that the area affected by the thermal neutron spillover from the target area is the six fuel assemblies outside the moderator (zirconium hydride). By comparing the fission power versus energy diagram of the fuel rod with the maximum fission power in the initial plan and the production plan, it is determined that the main contribution to the fission power in the production plan is thermal neutrons with energies within (1E-10MeV, 1E-3MeV), among which the fission power contribution of neutrons in the energy range of (3E-9MeV, 9E-7MeV) is the largest.

[0045] Step 4: Through the JANIS nuclide data visualization software, select materials with large reaction cross sections in the above energy range to reduce the fission power in the fuel assembly. Cadmium-113 with a very large reaction cross section near the (1E-11MeV, 5E-7MeV) energy range and gadolinium-157 with a very large reaction cross section near the (1E-11MeV, 2E-7MeV) energy group are selected as control materials.

[0046] Step 5: Place the control material around the moderator to form an optimization plan, perform critical calculations, and verify whether the fission power in the fuel rod decreases after the control material is placed. Adjust the control material parameters based on the results. Considering that the coolant flow around the fuel assembly will decrease after the control material is placed, the control material is placed near the target area and the thickness of the control material is as thin as possible.

[0047] Step 6: Perform neutron physics-thermal coupling calculations on the reactor models of the initial scheme, production scheme, and optimization scheme, and select pure cadmium-113 with a thickness of 0.01 cm as the optimization scheme (the best optimization scheme). Use the network mapping method to achieve the coupling of the computational fluid dynamics program (CFD program) and the neutron physics Monte Carlo program (MC program), and pass the coolant temperature, cladding temperature, air gap temperature, and fuel temperature calculated by the CFD program to the MC program. The MC program feeds back the reactor power distribution to the CFD program to obtain the coupling results of the component temperature in the center area of ​​the reactor, verifying the optimization effect of the neutron unidirectional flow technology.

[0048] Step 7: Evaluate the calculation results of the above scheme.

[0049] In this embodiment, by comparing the fission power distribution of the fuel area around the irradiation channel of the initial plan and the production plan (the irradiation channel mainly affects the surrounding fuel area), the control material is screened, and the screened control material is verified by nuclear thermal coupling calculation. The fission power distribution and the component temperature in the central area of ​​the initial plan, the production plan and the optimized plan are compared, as shown in Table 1.

[0050] Table 1. Relative fission powers of the initial scheme, production scheme, and optimized scheme.

[0051]

[0052]

[0053] Fission power ratio-1 refers to the ratio of the fission power of different optimization schemes to the fission power of the initial scheme, and fission power ratio-2 refers to the ratio of the fission power of different optimization schemes to the fission power of the production scheme. Fission power ratio-2 reflects the optimization effect for the production scheme, but compared with the initial scheme, the fission power is still higher than the initial scheme, which is reflected by fission power ratio-1. 10%, 25%, 50%, and 100% represent the percentage of the theoretical density of the controlled material, and 100% is the actual density. When the theoretical density reaches 100%, the relative content is adjusted by adjusting the thickness.

[0054] As shown in Table 1, after the placement of gadolinium-157 (Gd-157) or cadmium-113 (Cd-113) control materials, the fission power in the fuel rods around the irradiation channel decreased significantly. As the density and thickness of the control materials increase, the trend of fission power decreases more and more slowly. This is because the thermal neutron absorption cross-section of gadolinium-157 and cadmium-113 is very large. When the content of control materials is low, the neutrons in the thermal energy zone have been basically completely absorbed. The reason for the subsequent decrease in fission power is that the medium-energy neutrons are further absorbed by the control materials. The fission power after the placement of control materials is mainly contributed by the fission of medium-energy neutrons and fast neutrons.

[0055] like Figure 4-6 As shown in the figure, compared with the initial plan, the fission power of the fuel assembly in the core center area of ​​the production plan suddenly increases, the fission material content in the target material is low, and the fission cross section of the target material is relatively small. Although the thermal neutron flux at the target is greater than the thermal neutron flux at the fuel assembly, the fission power at the target is lower. After the control material is arranged, the fission power of the fuel assembly around the irradiation channel in the production plan is significantly reduced. Figure 7 The variation of relative fission power of fuel rods around the irradiation channel with energy in the initial scheme and production scheme is given, and it can be determined that the peak fission power appears in the energy range of (1E-8MeV, 1E-7MeV). Figure 8 and Fig. 9The curves of total reaction cross sections of cadmium-113 and gadolinium-157 changing with energy are given. For these two materials, the cross sections of thermal neutron reactions are larger than those of fast neutron reactors.

[0056] The results of nuclear thermal coupling calculation are as follows Figure 10-12 As shown in the figure, the target area is constructed, and the thermal neutrons slowed down by the moderator overflow to the fuel area around the irradiation channel, resulting in an increase in the fission power of the fuel area, a sudden rise in the temperature of the fuel assembly, and a maximum temperature of the production plan of more than 5000K. After the control material is arranged, the problem of thermal neutron overflow is alleviated, the fission power of the fuel area around the irradiation channel decreases, the temperature of the fuel assembly decreases, and the maximum temperature is about 2028K. Compared with the traditional high-flux reactor, this technology realizes the unidirectional flow of neutrons in the ultra-high-flux fast neutron reactor, restricts the flow of thermal neutrons to the fuel area, and controls the thermal neutrons within the target area. This technology ensures the irradiation production efficiency, reduces the fission power and temperature of the fuel area around the irradiation channel, and enables the ultra-high-flux fast neutron reactor to have the ability to produce super-plutonium isotopes while improving safety and economy.

[0057] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation, characterized in that: Moderators and control materials are arranged around the irradiation channel of the ultra-high flux fast neutron reactor. By comparing and analyzing the fission power of the initial plan of the ultra-high flux fast neutron reactor and the fission power before and after the control material is arranged, the control material is selected to reduce the fission power of the fuel area and realize the one-way flow of neutrons. The control material is cadmium-113 or gadolinium-157.

2. The neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation according to claim 1, characterized in that: The ultra-high flux fast neutron reactor initial scheme is an initial reactor scheme without the arrangement of moderators and control materials.

3. The neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation according to claim 1, characterized in that: The fission power before the control material is arranged is the fission power distribution of the fuel area around the irradiation channel after only the moderator is arranged.

4. The neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation according to claim 1, characterized in that: The fission power after the control material is arranged is the fission power distribution of the fuel area around the irradiation channel after the moderator and the control material are arranged at the same time.

5. The neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation according to claim 1, characterized in that: The arrangement is that the irradiation channel is located in the reactor fuel zone, the target is placed in the center of the irradiation channel, the moderator surrounds the periphery of the target, and the control material surrounds the periphery of the moderator.

6. The neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation according to claim 1, characterized in that: The method specifically comprises the following steps: Step 1: Model the initial scheme of the ultra-high flux fast neutron reactor, perform criticality calculations, and obtain the full-stack fission power distribution of the initial scheme; Step 2: Construct irradiation channels at the central assembly of the ultra-high flux fast neutron reactor, arrange moderators and targets, perform criticality calculations, and obtain the full-stack fission power distribution of the production plan; Step 3: Compare the fission power distribution of the fuel area around the irradiation channel of the initial scheme and the production scheme, and select the control material in the nuclear database according to the difference in fission power distribution between the two schemes; Step 4: Arrange control materials in the irradiation channel. The arrangement of control materials in the irradiation channel is referred to as the optimization plan. By comparing the fission power distribution of the production plan and the optimization plan, the control materials and arrangement plans are screened to obtain the best optimization plan.

7. The neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation according to claim 6, characterized in that: After step 4, execute: Step 5: By performing neutron physics-thermal coupling calculations on the reactor models of the initial scheme, production scheme, and optimized scheme, the fission power distribution of the fuel area around the irradiation channel is obtained to verify the technical effect of the neutron unidirectional flow method.

8. The neutron unidirectional flow method for producing super plutonium isotopes based on ultra-high flux fast neutron reactor irradiation according to claim 1, characterized in that: The method arranges the control material between the fuel zone and the moderator zone, and the fast neutrons generated by the fission of the nuclear fuel pass through the control material and enter the moderator zone and the target zone, thereby being moderated into thermal neutrons for irradiation production. The thermal neutrons in the target zone are absorbed after contacting the control material and cannot reach the fuel zone, and will not induce fission.

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