Fast neutron reactor core with optimized irradiation

Abstract

The invention relates to a fast neutron reactor core with optimized irradiation. The fast neutron reactor core comprises a reflecting layer with a hollow cylinder structure and an active region positioned in the reflecting layer, the active area comprises a coolant located outside, a central irradiation pore channel located in the center, peripheral irradiation pore channels symmetrically arranged in pairs relative to the center, an adjusting rod assembly, a safety rod assembly and a plurality of fuel assemblies arranged in the coolant, and the peripheral irradiation pore channels, the adjusting rod assembly and the safety rod assembly are located on the side length of a hexagon in the center. Under the condition that the thermal power is less than or equal to 210 MW, the maximum neutron flux in the reactor core is greater than or equal to 1.30 * 10 < 16 > cm <-2 > s <-1 >, the average neutron flux of the central irradiation pore channel is greater than or equal to 1.20 * 10 < 16 > cm <-2 > s <-1 >, the volume of the central irradiation pore channel is greater than or equal to 10000 cm < 3 >, and the fuel circulation period is greater than or equal to 100 equivalent full power days. And the neutron flux level and the irradiation capability of the reactor are obviously improved. Meanwhile, reactor core thermal hydraulic analysis is carried out based on the reactor, the highest temperature of a fuel pellet is smaller than or equal to 536 DEG C, the highest temperature of a cladding is smaller than or equal to 505 DEG C, and the highest temperature of a coolant is smaller than or equal to 456 DEG C. All thermal parameters of the hottest assembly meet thermal design criteria.

Description

Technical Field

[0001] The present invention relates to a technology in the field of nuclear reactors, specifically a fast neutron reactor core with optimized irradiation. Background Art

[0002] High-flux reactors are important experimental facilities for the development of nuclear energy. The high neutron flux level can meet various neutron-based scientific research and engineering applications, including materials science research under real irradiation conditions, production of radioactive isotopes, neutron science research, etc. The overall flux level of existing reactors still remains at the order of 10 15 magnitude, and the irradiation capacity of the reactor core has not been significantly improved. The higher the neutron flux of the reactor, the shorter the time required for irradiation experiments and isotope production. Therefore, there is an urgent need for a new type of high-flux reactor with stronger irradiation ability. Summary of the Invention

[0003] Aiming at the deficiencies of the existing fast neutron reactor technology, where the neutron flux level of the reactor core is too low to meet the demand for efficient production of scarce isotopes and the volume of the central irradiation channel is too small to provide a large-volume high-flux irradiation environment, the present invention proposes a fast neutron reactor core with optimized irradiation. Under the condition that the thermal power is less than or equal to 210 MW, the maximum neutron flux in the reactor core is greater than or equal to 1.30×10 16 cm -2 s -1 , the average neutron flux of the central irradiation channel is greater than or equal to 1.20×10 16 cm - 2 s -1 , the volume of the central irradiation channel is greater than or equal to 10000 cm 3 , and the fuel cycle period is greater than or equal to 100 equivalent full-power days. The neutron flux level and irradiation ability of the reactor are significantly improved. At the same time, based on this reactor, a core thermal-hydraulic analysis has been carried out. The maximum temperature of the fuel pellet is less than or equal to 536 °C, the maximum temperature of the cladding is less than or equal to 505 °C, and the maximum temperature of the coolant is less than or equal to 456 °C. All thermal-hydraulic parameters of the hottest component meet the thermal design criteria.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention relates to a fast neutron reactor core with optimized irradiation, including: a reflector in the form of a hollow cylinder structure and an active zone located inside it.

[0006] The reflector includes axial reflectors located at the top and bottom and a radial reflector located therebetween.

[0007] The active region described above includes: coolant located on the outside, a central irradiation channel located at the center, peripheral irradiation channels symmetrically arranged in pairs relative to the center, regulating rod assemblies and safety rod assemblies, and a number of fuel assemblies disposed within the coolant, where: the peripheral irradiation channels, regulating rod assemblies, and safety rod assemblies are located on the side lengths of the hexagon at the center.

[0008] The fuel assembly described above includes a fuel plate structure arranged in multiple concentric layers and coolant flow channels located between adjacent fuel plate structures. Each layer of the fuel plate structure includes fuel pellets and claddings on its inner and outer walls, and a coolant flow channel is provided outside the outermost fuel plate structure.

[0009] Both the regulating rod assembly and the safety rod assembly include: a control rod support mechanical structure with a hexagonal structure and a number of control rod absorbers located therein. Technical effects

[0010] Based on the fuel-irradiation channel-fuel layout scheme, the present invention arranges six irradiation channels at the center of the reactor core, and retains a fuel assembly at the center of the irradiation channels as an internal neutron source to make up for the influence of the lack of fissile material on reactivity and neutron flux. Supplementary measures include using plutonium-239 as the main nuclear fuel in the reactor core, and using materials with as small a neutron scattering cross-section as possible for the coolant, cladding, and structural materials. Compared with the prior art, the present invention obtains an ultra-high neutron flux environment (significantly higher than existing reactors) while meeting the requirements of reactor thermal-hydraulic design. The maximum neutron flux of the reactor is greater than 1.30×10 16 cm -2 s -1 , the average neutron flux of the irradiation channels is greater than 1.20×10 16 cm -2 s -1 , and an irradiation channel with a volume greater than 10000 cm 3 is constructed at the center of the reactor. Based on this reactor core, efficient production of californium-252 can be achieved, significantly improving the irradiation capacity of the reactor. Description of the drawings

[0011] Figure 1 is a schematic diagram of the radial structure of the reactor core of the present invention;

[0012] Figure 2 is a schematic diagram of the distribution of the active region components of the reactor core of the present invention;

[0013] Figure 3 is a schematic diagram of the structure of the fuel assembly of the present invention;

[0014] Figure 4 is a schematic diagram of the structures of the regulating rod assembly and the safety rod assembly of the present invention;

[0015] Figure 5Schematic diagram of the thermal-hydraulic calculation results of 1 / 4 core of the present invention;

[0016] In the figure: 1 Reflector, 2 Radial distribution of the active zone, 3 Outermost coolant in the active zone, 4 Coolant, 5 Fuel assembly, 6 Central fuel assembly, 7 Central irradiation channel, 8 First peripheral irradiation channel, 9 Second peripheral irradiation channel, 10 Regulating rod assembly, 11 Shutdown rod assembly, 12 Fuel pellets, 13 Cladding, 14 Coolant in the fuel plate gap, 15 Control rod absorber, 16 Control rod support mechanical structure, 17 Temperature distribution of 1 / 4 core, 18 Fuel temperature distribution of the hottest assembly, 19 Cladding temperature distribution of the hottest assembly, 20 Coolant temperature distribution of the hottest assembly. Specific implementation mode

[0017] As Figure 1 , this embodiment relates to a fast neutron reactor core with optimized irradiation, including: a reflector 1 with a hollow cylinder structure and an active zone 2 located inside it.

[0018] The radius of the active zone 2 is less than or equal to 60 cm.

[0019] The thickness of the reflector is greater than or equal to 150 cm. Setting a thicker reflector is beneficial to reducing the fuel loading in the active zone 2, and at the same time has a larger space volume for setting irradiation channels.

[0020] As Figure 2 shown, the active zone 2 includes: the outermost coolant 3 located outside, coolant 4, the central irradiation channel 7 located in the center, the peripheral irradiation channels 8, 9 symmetrically arranged in pairs relative to the center, the regulating rod assembly 10 and the safety rod assembly 11, and a number of fuel assemblies 5 and the central fuel assembly 6 arranged in the coolant 4, where: the peripheral irradiation channels 8, 9, the regulating rod assembly 10 and the safety rod assembly 11 are located on the side lengths of the hexagon in the center.

[0021] For the hexagon, the distance between the peripheral irradiation channels 8, 9 is used as the diameter.

[0022] The active zone shows a 1 / 4 symmetric arrangement, and the symmetry axes are the straight line where the center points of the peripheral irradiation channels 8, 9 are located and the straight line perpendicular to this line and passing through the center point of the reactor.

[0023] The total number of the fuel assemblies 5 and the central fuel assembly 6 is 103 and they are arranged in a honeycomb shape.

[0024] There are a total of 6 central irradiation channels 7 and they are arranged around the core center. The core center has the highest flux. Setting irradiation channels in the center can make full use of the neutrons in the reactor and maximize the irradiation capacity.

[0025] The radial cross-sections of the peripheral irradiation channels 8, 9 and the central irradiation channel 7 are circular.

[0026] As shown Figure 3 in the figure, in this embodiment, the fuel assembly 5 is a fuel plate structure with seven layers arranged concentrically and the coolant flow channels 14 located between adjacent fuel plate structures. Each layer of fuel plate structure includes fuel pellets 12 and claddings 13 on its inner and outer walls. The coolant flow channels 14 are outside the outermost fuel plate structure.

[0027] In other cases, the number of fuel plate structures can be adjusted on the premise of ensuring that the fuel volume and coolant fraction in the unit assembly meet the requirements of reactor physics and thermal-hydraulics.

[0028] The opposite side distance of the fuel assembly 5 is 6.39 cm, the thickness of the fuel pellets 12 is 0.13 cm, the thickness of the claddings 13 is 0.03 cm, and the thickness of the coolant flow channels 14 is 0.24 cm. In a single fuel assembly, the volume fraction of the coolant flow channels 14 is greater than or equal to 60%, which improves the heat transfer capacity of the core and is beneficial to the safety of the reactor.

[0029] In this embodiment, the fuel pellets 12 are made of U-20Pu-10Zr alloy fuel. As shown in Table 1, the average number of neutrons released by a single fission of Pu-239 is more. Under the condition of the same core thermal power, using Pu-239 as fuel, the core center flux level is higher and the fuel cycle period is longer.

[0030] In this embodiment, the claddings 13 are made of EP823 stainless steel. EP823 has a relatively high silicon content, which can enhance the oxidation resistance of the claddings and improve the coolant, thereby improving the heat transfer capacity of the core.

[0031] In this embodiment, the reflector 1 and the coolant 4 are made of liquid lead-bismuth alloy. Lead and bismuth have relatively large atomic numbers and have very little moderation effect on neutrons. The neutron flux is inversely proportional to the macroscopic fission cross-section. The fission cross-section of fast neutrons is 2-3 orders of magnitude smaller than that of thermal neutrons. The coolant and structural materials of this core are all selected materials with relatively small neutron scattering cross-sections to harden the neutron energy spectrum and provide the core flux level.

[0032] Table 1 Average fission neutrons and fission energy release of fissile nuclides

[0033] The radial cross-section of the regulating rod assembly 10 is a regular hexagon, with a total of 6.

[0034] The radial cross-section of the safety rod assembly 11 is a regular hexagon, with a total of 4.

[0035] As Figure 4As shown, the regulating rod assembly 10 and the safety rod assembly 11 both include: a control rod support mechanical structure 16 with a hexagonal structure and a number of control rod absorbers 15 located therein.

[0036] In this embodiment, there are 37 control rod absorbers 15 in total, and each has a radius of 0.4 cm.

[0037] The control rod absorbers of the regulating rod assembly 10 are made of natural abundance boron carbide.

[0038] The control rod absorbers of the safety rod assembly 11 are made of boron carbide with a B-10 abundance greater than 90%.

[0039] After modeling and simulating the reactor core with Monte Carlo software, at a power of 210 MW, the specific parameters of the reactor core are shown in Table 2 as follows:

[0040] Table 2 Comparison of the irradiation capabilities of this reactor core and a typical high-flux reactor

[0041] After Monte Carlo critical-burnup simulation calculations, at a power of 210 MW, a californium-252 production target is placed in the central irradiation channel 7 of the reactor core, irradiated for 90 days, and the production of californium-252 is counted. The results are shown in Table 3 as follows:

[0042] Table 3 Comparison of californium-252 production

[0043] As shown in Table 2 and Table 3, under the condition that the thermal power of the reactor core is less than or equal to 210 MW, the maximum neutron flux in the reactor core is greater than or equal to 1.30×10 16 cm -2 s -1 , the average neutron flux in the central irradiation channel 7 is greater than or equal to 1.20×10 16 cm -2 s -1 , the total volume of the central irradiation channel 7 is greater than or equal to 10000 cm 3 , and the fuel cycle period is greater than or equal to 100 equivalent full-power days. Its irradiation ability is significantly stronger than that of a typical high-flux reactor. As shown in Table 2, taking the production of californium-252 as an example, when a californium-252 production target is placed in the neutron irradiation channel 7 of this reactor core, the production and conversion rate of californium-252 in this reactor core are both much greater than those of HFIR in the case of a shorter total irradiation time.

[0044] After specific neutron physics-thermal hydraulics coupled calculation and simulation, the temperature distribution of 1 / 4 of the reactor core is obtained as Figure 5As shown in the figure, it can be seen that under the conditions that the thermal power of the present invention is less than or equal to 210 MW, the coolant flow rate is less than or equal to 4.5 m / s, and the inlet temperature of the reactor coolant is less than or equal to 157 °C, the maximum temperature of the fuel pellets is less than or equal to 536 °C, the maximum temperature of the cladding is less than or equal to 505 °C, and the maximum temperature of the coolant is less than or equal to 456 °C. All parameters meet the requirements of the thermal-hydraulic design, and the advanced core structure design improves the safety of the reactor.

[0045] Compared with the prior art, the present device has an ultra-high central flux level and excellent irradiation ability. The neutron flux is significantly higher than that of existing reactors, and the ultra-high neutron flux directly improves the irradiation intensity per unit time. The volume of the central irradiation channel of this core is much larger than that of existing reactors, and the large space volume can accommodate more irradiation targets and test samples. The daily irradiation ability can quantify the scale of irradiation resources for activities such as material irradiation experiments and isotope production in the reactor, and directly determines the irradiation ability of the reactor. The unit irradiation ability can measure the ability of the reactor to convert thermal energy into irradiation resources, and to a certain extent reflects the core design characteristics. The daily irradiation ability and unit irradiation ability of this core are significantly stronger than those of existing reactors, and can meet the needs of material irradiation tests and isotope production. Based on this core, efficient production of californium-252 can be achieved.

[0046] 1) Under the condition that the thermal power of the core of the present device is less than or equal to 210 MW, the maximum neutron flux in the core is greater than or equal to 1.30×10 16 cm -2 s -1 , the average neutron flux of the central irradiation channel is greater than or equal to 1.20×10 16 cm -2 s -1 , the total volume of the central irradiation channel is greater than or equal to 10000 cm 3 , and the fuel cycle period is greater than or equal to 100 equivalent full-power days. The irradiation ability is significantly stronger than that of existing high-flux reactors.

[0047] 2) Under the conditions that the thermal power of the core of the present device is less than or equal to 210 MW, the coolant flow rate is less than or equal to 4.5 m / s, and the inlet temperature of the coolant is less than or equal to 157 °C, the maximum temperature of the fuel pellets is less than or equal to 536 °C, the maximum temperature of the cladding is less than or equal to 505 °C, and the maximum temperature of the coolant is less than or equal to 456 °C. The advanced core structure design improves the safety of the reactor.

[0048] The above specific embodiments can be locally adjusted by those skilled in the art in different ways without departing from the principles and purposes of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above specific embodiments. All implementation schemes within its scope are subject to the present invention.

Claims

1. A fast neutron reactor core with optimized irradiation, characterized in that, Comprising: A reflector with a hollow cylinder structure and an active region located inside it. The active region includes: a coolant located on the outside, a central irradiation channel located at the center, peripheral irradiation channels symmetrically arranged in pairs relative to the center, a regulating rod assembly and a safety rod assembly, and a number of fuel assemblies arranged in the coolant, where: the peripheral irradiation channels, the regulating rod assembly, and the safety rod assembly are located on the side lengths of the hexagon at the center.

2. The fast neutron reactor core with optimized irradiation according to claim 1, characterized in that, The fuel assembly mentioned above includes a multi-layer concentric fuel plate structure and coolant flow channels located between adjacent fuel plate structures. Each layer of the fuel plate structure includes fuel pellets and cladding on its inner and outer walls, and a coolant flow channel is outside the outermost fuel plate structure.

3. The fast neutron reactor core with optimized irradiation according to claim 1, characterized in that, Both the regulating rod assembly and the safety rod assembly include: a control rod support mechanical structure with a hexagonal structure and a number of control rod absorbers located therein.

4. The fast neutron reactor core with optimized irradiation according to claim 1, characterized in that, The reflector mentioned above includes axial reflectors located at the top and bottom and a radial reflector located therebetween.

5. The fast neutron reactor core with optimized irradiation according to claim 1, characterized in that, The active region exhibits a 1 / 4 symmetry arrangement, and the axes of symmetry are the straight line where the center points of the peripheral irradiation channels are located and the straight line perpendicular to this line and passing through the center point of the reactor; There are a total of 103 fuel assemblies and central fuel assemblies, which are arranged in a honeycomb pattern; There are a total of 6 central irradiation channels, which are arranged around the center of the reactor core. The neutron flux at the center of the reactor core is the highest. Installing irradiation channels at the center can make full use of the neutrons in the reactor and maximize the irradiation capacity.

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