Energy spectrum adjustable long-life reactor core

Abstract

The invention relates to the technical field of nuclear reactors, and particularly discloses an energy-spectrum-adjustable long-life reactor core, which comprises a core active area, the core active area comprises a plurality of fuel assemblies, the cross section of each fuel assembly is hexagonal, the plurality of fuel assemblies are compactly arranged, each fuel assembly comprises a spectrum shift rod or a control rod, and the spectrum shift rods or the control rods are arranged in the reactor core active area. The fuel rods surround the spectrum shifting rod or the control rod; wherein in the three adjacent fuel assemblies, the center of at least one fuel assembly is provided with a control rod, and the center of at least one fuel assembly is provided with a spectrum shift rod. The independent spectrum shift rod is used in the reactor core of the fast neutron spectrum reactor, so that the energy spectrum of the reactor core is softened, the service life of the reactor core is effectively prolonged, the fuel utilization rate of the reactor core is improved, and the economical efficiency of the reactor is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor technology, and specifically discloses a long-life reactor core with tunable energy spectrum. Background Technology

[0002] Spectrum shift controlled reactors are a novel reactivity control method that uses a spectrum shift control strategy. At the beginning of the reactor's lifespan, the amount of moderator in the reactor core is reduced to harden the energy spectrum. Simultaneously, as the reactor approaches the end of its lifespan, a moderator is gradually introduced to soften the core energy spectrum. This is particularly relevant when neutron energies are in the lower energy range. 235 U has a higher fission cross section, meaning that thermal neutrons are more likely to initiate fission. 235 The fission reaction of U is therefore affected by the introduction of a moderator into the reactor. The moderation of neutrons leads to a decrease in neutron energy, making them more susceptible to fission. 235 The fission reaction of U enhances reactivity. The mechanism of spectrum shift reactivity control utilizes the above principle. When the reactor reactivity decreases due to factors such as power increase and burnup, positive reactivity is introduced by inserting a spectrum shift moderator into the core to compensate for the reactivity loss. When the reactor needs to introduce negative reactivity due to power reduction or shutdown, negative reactivity is introduced by removing the spectrum shift moderator from the core.

[0003] Spectrum shift control reactors, achieved through spectrum shift control technology, possess characteristics such as high fuel utilization, deep burnup, long lifespan, and high economic efficiency. Employing a spectrum shift reactor with an adjustable energy spectrum—characterized by a fast neutron spectrum at the beginning of its lifespan and a thermal neutron spectrum at the end—can reduce core reactivity during the initial, harder energy spectrum phase by lowering neutron value and increasing neutron leakage. Furthermore, it can also reduce core reactivity by increasing... 238 U increases the probability of capturing neutrons, improving the conversion of fissile nuclides, which gives spectro-shift reactors high fuel efficiency. As the reactor nears the end of its lifespan, a moderator is gradually introduced to moderate neutrons, increasing their value and reducing leakage, thus improving core reactivity. Since the critical mass of a typical thermal neutron reactor is less than that of a fast neutron reactor, the reactor can operate for an extended period, resulting in deep burnup and a long lifespan for spectro-shift reactors. Naturally, for the same energy output, compared to a simple fast neutron reactor, it saves uranium load, making it highly economical. However, current technologies often use spectro-shift materials as follower materials for the control rod absorbers. This typically involves making the spectro-shift rod and control rod into a single rod, which have opposite effects. Therefore, disturbances at their interface are very large, requiring an intermediate transition material, leading to high material consumption. Furthermore, this design increases the axial height of the core, resulting in a large core volume and hindering core miniaturization. Summary of the Invention

[0004] This invention provides a long-life reactor core with adjustable energy spectrum. By using independent spectral shifting rods in the fast neutron spectrum reactor core, the energy spectrum of the core is softened, effectively extending the core life, improving the core fuel utilization rate, and significantly improving the economics of the reactor.

[0005] This invention is achieved through the following technical solution: A long-life reactor core with tunable energy spectrum includes an active core region comprising multiple fuel assemblies. Each fuel assembly has a hexagonal cross-section and is arranged compactly. Each fuel assembly includes a spectral shift rod or a control rod, and multiple rings of fuel rods surrounding the spectral shift rod or control rod. In particular, among three adjacent fuel assemblies, at least one fuel assembly has a control rod at its center, and at least one fuel assembly has a spectral shift rod at its center.

[0006] Furthermore, the height of the active core region is 450-500 mm, and the equivalent diameter is 500-550 mm.

[0007] Furthermore, the fuel assembly contains 90 fuel rods with a center-to-center distance of 100-120 mm. A reserved channel with a diameter of 40-50 mm is provided at the center of the fuel assembly, and a control rod or spectral shifting rod is provided in the reserved channel.

[0008] Furthermore, the reserved channel is provided with a control rod guide tube or a spectrum shifting rod guide tube. The cross-section of the control rod guide tube and the spectrum shifting rod guide tube is hexagonal. The control rod is inserted into the control rod guide tube, and the spectrum shifting rod is inserted into the spectrum shifting rod guide tube.

[0009] Furthermore, the core active region includes 19 fuel assemblies, with spectral shift rods disposed at the center of 10 fuel assemblies and control rods disposed at the center of 9 fuel assemblies.

[0010] Furthermore, each of the control rods includes a casing and an absorber disposed within the casing. The absorber has a diameter of 43 mm and is made of B4C material. The casing has a thickness of 1-3 mm and is made of HT9 stainless steel.

[0011] Furthermore, each of the spectral shift bars includes a casing and an absorber disposed within the casing. The absorber has a diameter of 43 mm and is made of ZrH2O. 1.6 The shell thickness is 1-3mm and the material is HT9 stainless steel.

[0012] Furthermore, the control rod is divided into a compensation rod group C1 and a safety rod group C2, and the spectral shift rod is divided into a compensation rod group S1, a compensation rod group S2 and a compensation rod group S3.

[0013] Furthermore, the fuel rod includes a casing and a UO2 pellet installed inside the casing. The UO2 pellet has a diameter of 7.6 mm, and the casing has a thickness of 0.6-1.4 mm and is made of HT9 stainless steel.

[0014] The technical solution of the present invention has at least the following advantages and beneficial effects: This invention employs an independent control rod and spectral shift rod design, instead of using spectral shift material as a follower material for the control rod absorber. On the one hand, this eliminates the need for additional transition material, resulting in lower material consumption, and overcomes the problem of significant disturbance at the junction. On the other hand, it reduces the overall core axial height extension caused by using a follower design, making core miniaturization easier.

[0015] The reactor core of the present invention can achieve high burnup and significantly extend the core life. Without the introduction of spectrometer shifting rods, reactivity can only be maintained for a burnup life of 1800 EFPD. After the introduction of spectrometer shifting rods, the life can be extended to 4000 EFPD.

[0016] The reactor core of this invention can improve fuel utilization and significantly improve the economics of the reactor. Compared with the core scheme using a single fast spectrum of equivalent energy output, the amount of fissile nuclides is reduced by 28.6%. Attached Figure Description

[0017] Figure 1 This is a cross-sectional schematic diagram of the fuel assembly provided in Embodiment 1 of the present invention.

[0018] Figure 2 This is a schematic diagram of the reactor core loading structure provided in Embodiment 1 of the present invention.

[0019] Figure 3 This is a schematic diagram of the control rod provided in Embodiment 1 of the present invention.

[0020] Figure 4 This is a schematic diagram of the spectral shifter provided in Embodiment 1 of the present invention.

[0021] Figure 5 This is a schematic diagram of the arrangement of spectral shifting rods and control rods in the reactor core provided in Embodiment 1 of the present invention.

[0022] Figure 6 Provided for Embodiment 1 of the present invention 235 A schematic diagram illustrating the change in Keff with fuel consumption under full rod-raising conditions in the fast spectrum scheme with a U enrichment of 70%.

[0023] Figure 7 Provided for Embodiment 1 of the present invention 235 A schematic diagram illustrating the change in Keff with fuel consumption under full rod-raising conditions in the fast spectrum scheme with a U enrichment of 50%.

[0024] Figure 8 Provided for Embodiment 1 of the present invention 235 A schematic diagram illustrating the change of Keff with fuel consumption under the fully inserted state of the spectral shift rod after introducing the spectral shift rod in the fast spectrum scheme with a U enrichment of 50%.

[0025] Figure reference numerals: 1-Core active zone, 2-Fuel assembly, 3-Control rod guide tube, 4-Control rod, 5-Spectrum shift rod guide tube, 6-Spectrum shift rod, 7-Fuel rod. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0027] Example 1 Reference Figures 1-2 A long-life reactor core with tunable energy spectrum includes a core active region 1, wherein the core active region 1 includes multiple fuel assemblies 2, the cross-section of each fuel assembly 2 is hexagonal, the multiple fuel assemblies 2 are arranged compactly, each fuel assembly 2 includes a spectrum shifting rod 6 or a control rod 4, and multiple rings of fuel rods 7 surrounding the spectrum shifting rod 6 or the control rod 4; wherein, in at least one of three adjacent fuel assemblies 2, a control rod 4 is disposed at the center of at least one fuel assembly 2, and a spectrum shifting rod 6 is disposed at the center of at least one fuel assembly 2.

[0028] Fuel assembly 2 is hexagonal in shape and uses a boxless design, positioned via wire winding. At its center is either the control rod guide tube 3 or the spectral shift rod guide tube 5. It employs an independent single-rod bundle design for control rods 4 and spectral shift rods 6, avoiding the use of spectral shift material as a follower material for the control rods 4 absorbers. This design reduces the overall core axial height increase that would result from using a follower material, facilitating core miniaturization. The core power is 8MW, and its service life is 4000 EFPD.

[0029] In this embodiment, the height of the core active region 1 is 450-500mm, and the equivalent diameter is 500-550mm.

[0030] In this embodiment, the fuel assembly 2 is provided with 90 fuel rods 7, the center distance of the fuel assembly is 100-120mm, a reserved channel is provided at the center of the fuel assembly 2, the diameter of the reserved channel is 40-50mm, and a control rod 4 or a spectrum shifting rod 6 is provided in the reserved channel.

[0031] In this embodiment, the reserved channel is provided with a control rod guide tube 3 or a spectrum shifting rod guide tube 5. The cross-section of the control rod guide tube 3 and the spectrum shifting rod guide tube 5 is hexagonal. The control rod 4 is inserted into the control rod guide tube 3, and the spectrum shifting rod 6 is inserted into the spectrum shifting rod guide tube 5.

[0032] In this embodiment, the core active region 1 includes 19 fuel assemblies 2, with spectral shift rods 6 disposed at the center of 10 fuel assemblies 2 and control rods 4 disposed at the center of 9 fuel assemblies 2.

[0033] Reference Figure 3 The control rod 4 adopts a single rod bundle design. Each control rod 4 includes a shell and an absorber disposed in the shell. The absorber has a diameter of 43mm and is made of B4C material. The shell has a thickness of 1-3mm and is made of HT9 stainless steel.

[0034] Reference Figure 4 The spectral shifter 6 adopts a single-bar bundle design. Each spectral shifter 6 includes a shell and an absorber disposed within the shell. The absorber has a diameter of 43 mm and is made of ZrH2O. 1.6 The shell thickness is 1-3mm and the material is HT9 stainless steel.

[0035] Reference Figure 5 The arrangement of the spectrum shifting rod 6, control rod 4 and fuel assembly 2 in the active region 1 of the reactor core is as follows: the control rod 4 is divided into a compensation rod group C1 and a safety rod group C2, and the spectrum shifting rod 6 is divided into a compensation rod group S1, a compensation rod group S2 and a compensation rod group S3.

[0036] Safety rod group C2 is in a fully raised state throughout its entire lifespan and is used for normal and emergency shutdowns. Compensation rod group C1 is used for burnup compensation at the beginning of the lifespan. Compensation rod groups S1, S2, and S3 of spectrum shift rod 6 are all used for burnup compensation during operation. From the middle to the end of the lifespan, they are gradually inserted into the core in the order of S1-S2-S3 to soften the core energy spectrum, compensating for the reactivity loss caused by burnup, achieving deep burnup, extending core lifespan, and improving fuel utilization, significantly improving reactor economics. During normal or emergency shutdowns, all rod groups of spectrum shift rod 6 are removed from the core. The specific control strategy is: C2↑-C1↑-S1↓-S2↓-S3↓, that is, during reactor core operation, C2 is removed, C1 is removed, S1 is inserted, S2 is inserted, and S3 is inserted.

[0037] The active zone 1 of the reactor core contains 19 fuel assemblies 2, with a total of 10 spectral shifting rods 6 and 9 control rods 4. Using the aforementioned spectral shifting strategy, all control rods 4 are lifted at 1800 EFPD, and spectral shifting rods 6 are gradually inserted at that time until the end of the core's lifespan. This extends the core's lifespan to 4000 EFPD, and compared to a core scheme using a single fast spectrum with equivalent energy output, the amount of fissile nuclides is reduced by 28.6%.

[0038] In this embodiment, the fuel rod 7 includes a casing and a UO2 pellet installed inside the casing. The UO2 pellet has a diameter of 7.6 mm, the casing has a thickness of 0.6-1.4 mm, and the material is HT9 stainless steel.

[0039] Based on the design of fuel assembly 2, core, and control rods 4, the core fuel enrichment is designed with a core thermal power of 8MW and a lifespan of 4000 EFPD as the design objectives. By adjusting the fuel enrichment, the core criticality and burnup life requirements are met. Calculations are performed to determine the optimal fuel enrichment levels for the core. 235 When the U enrichment is 70%, the core design can meet the power and lifespan requirements (the full rod lifting calculation results are as follows). Figure 6 (As shown), the corresponding fissile nuclides 235 The U-fill weight is 296.55 kg.

[0040] Based on the above-mentioned spectral shift reactivity control scheme, further research was conducted on the basis of the fast-spectrum reactor core. 235 U-packing optimization reduced enrichment to 50%. Figure 7 The variation of core Keff with burnup lifetime under the fully raised control rod 4 state is presented when the spectral shift rod 6 is not used and the core exhibits a fast spectrum throughout its entire lifespan. It can be seen that without the spectral shift rod 6, when the enrichment level is reduced to 50%, the core Keff under the fully raised control rod state is less than 1.0 when the burnup lifetime reaches 1800 EFPD, making it impossible to maintain core criticality. At this point, inserting the spectral shift rod 6 into the core softens the neutron spectrum, introduces positive reactivity, and allows the core to re-reach the critical state. Figure 8 The changes in reactivity after inserting spectral shift rod 6 at 1800 EFPD (with spectral shift rod 6 fully inserted) are presented. It can be seen that at 4000 EFPD, with spectral shift rod 6 fully inserted, the core Keff is still greater than 1.01, indicating sufficient reserve reactivity to maintain criticality. That is, through reactivity control design, by fully lifting control rod 4 at 1800 EFPD and gradually inserting spectral shift rod 6 from that moment until the end of the core's lifespan, the core lifespan can be extended to 4000 EFPD. Calculations show that the core at this time... 235 The U-pack weight is 211.88 kg, which is 84.67 kg less than the fast spectrum scheme, resulting in a total reduction of 28.6% in the amount of fissile nuclides.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A spectrum-tunable long-lived reactor core, characterized in that, The core active zone comprises a plurality of fuel assemblies, the cross section of the fuel assemblies is hexagonal, the plurality of fuel assemblies are compactly arranged, the fuel assemblies comprise a spectrum shift rod or a control rod, and a plurality of fuel rods surround the spectrum shift rod or the control rod; wherein, among the three adjacent fuel assemblies, at least one fuel assembly is provided with the control rod at the center thereof, and at least one fuel assembly is provided with the spectrum shift rod at the center thereof.

2. The energy-tunable long-life reactor core of claim 1, wherein, The core active zone has a height of 450-500 mm and an equivalent diameter of 500-550 mm.

3. The energy-tunable long-life reactor core of claim 1, wherein, The fuel assembly is provided with 90 fuel rods, the center-to-center distance of the fuel assemblies is 100-120 mm, the fuel assembly is provided with a reserved hole at the center thereof, the reserved hole has a diameter of 40-50 mm, and the reserved hole is provided with the control rod or the spectrum shift rod.

4. The energy spectrum adjustable long-life reactor core of claim 3, wherein, The reserved hole is provided with a control rod guide tube or a spectrum shift rod guide tube, the cross section of the control rod guide tube and the spectrum shift rod guide tube is hexagonal, the control rod is inserted into the control rod guide tube, and the spectrum shift rod is inserted into the spectrum shift rod guide tube.

5. The energy-tunable long-life reactor core of claim 1, wherein, The core active zone comprises 19 fuel assemblies, the center of 10 fuel assemblies is provided with the spectrum shift rod, and the center of 9 fuel assemblies is provided with the control rod.

6. The energy spectrum adjustable long-life reactor core of claim 5, wherein, Each control rod comprises a cladding and an absorber arranged in the cladding, the absorber has a diameter of 43 mm and is made of B4C, and the cladding has a thickness of 1-3 mm and is made of HT9 stainless steel.

7. The energy spectrum adjustable long-life reactor core of claim 5, wherein, Each of the spectrum shift rods includes a cladding and an absorber disposed within the cladding, the absorber having a diameter of 43 mm and being made of ZrH 1.6 , the cladding having a thickness of 1-3 mm and being made of HT9 stainless steel.

8. The energy spectrum adjustable long-life reactor core of claim 5, wherein, The control rods are divided into a compensation rod group C1 and a safety rod group C2, and the spectrum shift rods are divided into a compensation rod group S1, a compensation rod group S2 and a compensation rod group S3.

9. The energy-tunable long-life reactor core of claim 1, wherein, The fuel rod comprises a cladding and a UO2 pellet arranged in the cladding, the UO2 pellet has a diameter of 7.6 mm, and the cladding has a thickness of 0.6-1.4 mm and is made of HT9 stainless steel.

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