A Modular Prismatic High-Temperature Gas-Cooled Reactor Power Distribution Optimization Method

Abstract

The present invention discloses a method for optimizing the power distribution of a modular prismatic high temperature gas-cooled reactor, including: determining the average enrichment, the ratio factor of the enrichment of fuel assemblies in radial zones, and the ratio factor of the enrichment of fuel assemblies in axial layers; determining the enrichment of each fuel assembly according to the average enrichment, the ratio factor of the enrichment of fuel assemblies in radial zones, and the ratio factor of the enrichment of fuel assemblies in axial layers; and outputting the optimization result according to the enrichment of each fuel assembly. The beneficial effect of the present invention is that the present invention optimizes the enrichment of fuel assemblies at different positions according to the partitioned and layered arrangement, can effectively optimize the core power distribution, make the maximum temperature of the core fuel as low as possible, improve the core temperature rise margin, and ensure the realization of the inherent safety of the core.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear reactor engineering, and in particular relates to a modular prismatic high-temperature air-cooled power distribution optimization method. Background Art

[0002] The rapid economic development has increased the demand for energy, but traditional fossil fuels such as coal will bring serious environmental problems, which has prompted my country to continuously explore and develop clean energy. Among various types of new energy, nuclear energy has the advantages of cleanliness, high energy density, almost no greenhouse gas emissions, and low fuel transportation pressure.

[0003] The modular prismatic high-temperature gas-cooled reactor is an advanced reactor type belonging to the fourth-generation nuclear energy system, with superior inherent safety. The ceramic fuel particles used in this reactor type can effectively prevent the release of fission products; the graphite core has a large heat capacity and slow temperature transient, can withstand very high temperatures, and has a large emergency operation time margin; the core power density is small, and it has a strong temperature negative feedback. Under accident conditions, even if there are no emergency measures, the temperature negative feedback can be relied on to shut down the reactor to ensure the structural integrity of the core and fuel. The modular and miniaturized design can not only simplify emergency measures, but also make the core have extremely strong design flexibility and environmental adaptability. It has great market potential in the fields of power supply in remote mountainous areas, aerospace, island power supply, and deep-sea power supply.

[0004] The fuel temperature limit is one of the main limitations of the modular prismatic high-temperature gas-cooled reactor. When the fuel temperature is too high, the core temperature rise margin will be reduced, and the temperature negative feedback will not be able to introduce enough negative reactivity, which may make the core unable to shut down relying solely on temperature negative feedback, and the inherent safety of the core will be destroyed; under accident conditions, the fuel temperature may also exceed the temperature limit, resulting in a significant increase in the breakage rate of ceramic fuel particles and the release of radioactive substances such as fission products. Therefore, optimizing the core power distribution to ensure that the maximum temperature of the fuel in the core is as low as possible will be conducive to the realization of the inherent safety of the modular prismatic high-temperature gas-cooled reactor.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] In view of the defects existing in the prior art, the purpose of the present invention is to provide a modular prismatic high-temperature gas-cooled reactor power distribution optimization method, which can optimize the power distribution, improve the core temperature rise margin, and ensure the realization of the inherent safety of the core.

[0007] The technical solution of the present invention is:

[0008] A method for optimizing power distribution of a modular prismatic high temperature gas-cooled reactor, comprising:

[0009] Determine the average enrichment, the ratio factor of the fuel assembly enrichment in each radial zone and the ratio factor of the fuel assembly enrichment in each axial layer;

[0010] The enrichment of each fuel assembly is determined based on the average enrichment, the ratio factor of the enrichment of the fuel assemblies in each radial zone, and the ratio factor of the enrichment of the fuel assemblies in each axial layer;

[0011] Output optimization results based on the enrichment of each fuel assembly.

[0012] Furthermore, in the above-mentioned modular prismatic high temperature gas-cooled reactor power distribution optimization method, the enrichment of each fuel assembly is determined according to the average enrichment, the ratio factor of the radial fuel assembly enrichment in each zone and the ratio factor of the axial fuel assembly enrichment in each layer according to the following formula:

[0013] Cwt=Cav*Er*Ez;

[0014] In the above formula, Cwt is the enrichment of each fuel assembly;

[0015] Cav is the average enrichment;

[0016] Er is the radial enrichment ratio factor;

[0017] Ez is the axial enrichment ratio factor.

[0018] Furthermore, in the above-mentioned modular prismatic high temperature gas-cooled reactor power distribution optimization method, the method for determining the radial zone fuel assembly enrichment ratio factor is:

[0019] When the fuel enrichment of the whole reactor is the same, calculate the neutron flux distribution of the radial fuel assembly in the core;

[0020] According to the ratio of the inverse of the radial fuel neutron flux, the enrichment ratio factor of the fuel assembly in each radial zone is determined.

[0021] Furthermore, in the above-mentioned modular prismatic high temperature gas-cooled reactor power distribution optimization method, the method for determining the enrichment ratio factor of each axial layer of fuel assemblies is:

[0022] The formula P(z)=C·exp(-a·z / b) is used to calculate the enrichment ratio factor of each layer of the fuel assembly in the axial direction so that the axial power distribution is approximately distributed in the form of an exponential function.

[0023] Furthermore, in the above-mentioned modular prismatic high temperature gas-cooled reactor power distribution optimization method, before outputting the optimization result according to the enrichment of each fuel assembly, similar enrichment parameters are approximated to reduce the types of fuel enrichment in the whole stack.

[0024] Furthermore, in the above-mentioned modular prismatic high-temperature gas-cooled reactor power distribution optimization method, the approximate processing of similar enrichment parameters is to perform weighted average processing of similar enrichments using the number of fuel assemblies corresponding to similar enrichments as weights.

[0025] Furthermore, in the above-mentioned modular prismatic high-temperature gas-cooled reactor power distribution optimization method, the similar enrichment parameters are determined based on reducing the types of fuel enrichment of the entire reactor to six.

[0026] The beneficial effects of the present invention are:

[0027] 1. The present invention optimizes the enrichment of fuel assemblies at different positions according to the partitioned and layered arrangement, which can effectively optimize the core power distribution, make the maximum temperature of the core fuel as low as possible, increase the core temperature rise margin, and ensure the realization of the inherent safety of the core.

[0028] 2. Through the technical solution of the present invention, the power is flattened as much as possible in the radial direction to reduce the radial power peak factor; in the axial direction, the power distribution is spread in the form of an approximate exponential function; the maximum temperature of the modular prismatic high-temperature gas-cooled reactor fuel is minimized, the core temperature rise margin is increased, the integrity of the core structure and fuel is ensured, and it is conducive to further improving the inherent safety of the core. The present invention can effectively reduce the maximum temperature of the fuel and can be applied in the design of the prismatic high-temperature gas-cooled reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a flowchart of a method for optimizing power distribution of a modular prismatic high-temperature gas-cooled reactor.

[0030] Figure 2 This is a radial layout diagram of the modular prismatic high-temperature gas-cooled reactor of the present invention.

[0031] Figure 3 This is an axial layout diagram of the modular prismatic high-temperature gas-cooled reactor of the present invention.

[0032] Figure 4 This is a fuel characteristic curve diagram after the core fuel enrichment zoning arrangement of the present invention.

[0033] Figure 5 The present invention provides a core neutron spectrum diagram before and after the core fuel enrichment zoning arrangement.

[0034] Figure 6 This is the normalized power distribution diagram before core optimization of the present invention.

[0035] Figure 7 This is the normalized power distribution diagram after the core optimization of the present invention.

[0036] Figure 8 This is the average fuel temperature distribution diagram before and after the core power distribution optimization of the present invention.

[0037] Fig. 9 This is the maximum fuel temperature distribution diagram before and after the core power distribution optimization of the present invention.

[0038] In the above figures: 1. fuel assembly; 2. control rod assembly; 3. side reflector; 4. control rod channel; 5. upper reflector; 6. lower reflector. DETAILED DESCRIPTION

[0039] The embodiments of the present invention are described below in conjunction with the accompanying drawings:

[0040] like Figure 1 As shown, the present invention provides a modular prismatic high temperature gas-cooled reactor power distribution optimization method, comprising:

[0041] S100 determines the average enrichment, the ratio factor of the fuel assembly enrichment in each radial zone, and the ratio factor of the fuel assembly enrichment in each axial layer;

[0042] S200 determines the enrichment of each fuel assembly according to the average enrichment, the ratio factor of the enrichment of the fuel assemblies in each radial zone, and the ratio factor of the enrichment of the fuel assemblies in each axial layer;

[0043] S300 outputs optimization results based on the enrichment of each fuel assembly.

[0044] In S200, the enrichment of each fuel assembly is determined according to the average enrichment, the ratio factor of the radial enrichment of the fuel assembly in each zone, and the ratio factor of the axial enrichment of the fuel assembly in each layer according to the following formula:

[0045] Cwt=Cav*Er*Ez;

[0046] In the above formula, Cwt is the enrichment of each fuel assembly;

[0047] Cav is the average enrichment;

[0048] Er is the radial enrichment ratio factor;

[0049] Ez is the axial enrichment ratio factor.

[0050] The present invention optimizes the enrichment of fuel assemblies at different positions according to the layered arrangement, can effectively optimize the core power distribution, make the maximum temperature of the core fuel as low as possible, increase the core temperature rise margin, and ensure the realization of the inherent safety of the core.

[0051] In S100, the method for determining the radial enrichment ratio factor of the fuel assembly in each zone is:

[0052] When the fuel enrichment of the whole reactor is the same, calculate the neutron flux distribution of the radial fuel assembly in the core;

[0053] According to the ratio of the inverse of the radial fuel neutron flux, the enrichment ratio factor of the fuel assembly in each radial zone is determined.

[0054] In this way, the power can be flattened as much as possible in the radial direction and the radial power peak factor can be reduced.

[0055] In S100, the method for determining the enrichment ratio factor of each axial layer of fuel assembly is:

[0056] The formula P(z)=C·exp(-a·z / b) is used to calculate the enrichment ratio factor of each layer of the fuel assembly in the axial direction so that the axial power distribution is approximately distributed in the form of an exponential function.

[0057] In this way, the maximum temperature of the modular prismatic high-temperature gas-cooled reactor fuel is kept as low as possible, the core temperature rise margin is increased, the integrity of the core structure and fuel is ensured, and it is beneficial to further improve the inherent safety of the core.

[0058] The above formula P(z) = C·exp(-a·z / b) is derived and determined by the following formula:

[0059] T fuel (z) = T in +T cool (z)+T r (z);

[0060]

[0061] T r (z) = bP(z);

[0062] Among them, T fuel (z) represents the fuel temperature at the axial position z, T in represents the coolant inlet temperature, T cool (z) represents the temperature change of the coolant from the inlet to the z point, T r (z) represents the temperature change caused by radial heat conduction from the coolant channel to the inner surface of the fuel core at position z, P(z) represents the axial power distribution, a and b represent constants related to the coolant properties and the core geometry, C is the normalization coefficient, and z represents the axial position of the core.

[0063] The maximum temperature of the fuel is generally located inside the fuel pellet, because the coolant inlet temperature T in is a constant, and the total core power is a fixed value. In order to improve the safety of the core, the fuel temperature T fuel The maximum value of (z) is the smallest, that is, T fuel (z) is a constant. At this point, the above-mentioned axial power distribution P(z) can be derived, and the axial power should be distributed in the form of an exponential function.

[0064] In order to reduce the process difficulty, before outputting the optimization results according to the enrichment of each fuel assembly, similar enrichment parameters are approximated to reduce the types of fuel enrichment in the whole stack.

[0065] The approximate processing of similar enrichment parameters is to perform weighted average processing of similar enrichments using the number of fuel assemblies corresponding to similar enrichments as weights.

[0066] In this embodiment, the determination of the similar enrichment parameters is based on reducing the types of fuel enrichments in the entire stack to six or less.

[0067] The present invention can effectively reduce the maximum temperature of fuel and can be applied in the design of prismatic high-temperature gas-cooled reactors.

[0068] The power distribution optimization method of the modular prismatic high temperature gas-cooled reactor of the present invention is applied to a core arrangement of a modular prismatic high temperature gas-cooled reactor with a thermal power of 15MW and a service life of 20 years. The radial diagram and axial diagram of the core are as follows: Figure 2 and Figure 3 As shown. The core is mainly composed of a fuel assembly 1, a control rod assembly 2 and a reflector. The reflector includes a side reflector 3, an upper reflector 5 and a lower reflector 6. In this embodiment, the fuel assembly is divided into 4 zones in the radial direction according to different positions, namely zone 1 to zone 4; it is divided into 6 layers in the axial direction, namely layer 1 to layer 6 from top to bottom; the fuel assembly is composed of fuel rods and coolant channels in which ceramic fuel particles are dispersed in a silicon carbide matrix. Each fuel assembly has 54 fuel rods and 19 coolant channels. The hexagonal fuel assembly has a side-to-side distance of 35.7 cm and a height of 70 cm. There are 7 groups of control rod assemblies arranged in the active zone and 6 groups arranged in the reflector. The core structural material and the reflector are made of graphite. The entire core has a diameter of 280 cm and a height of 595 cm. In order to meet the core design objectives, the average enrichment of the core fuel is 9%. At this time, the core life is 7360 EFPD.

[0069] When the fuel enrichment is 9%, the neutron flux distribution of the radial 4-zone fuel assembly can be obtained. Since power is related to neutron value, and neutron value is proportional to the square of neutron flux, if the fuel enrichment is arranged in zones according to the inverse of the square of radial neutron flux, the radial power peak factor will be very small, close to 1, but this will cause the fuel enrichment gradient in the core to be too large, and the enrichment of some fuel assemblies will exceed the limit (for example, the uranium enrichment of civilian nuclear facilities is generally less than 20%). Therefore, according to the ratio of the inverse of the neutron flux of the radial 4-zone fuel assembly, the radial zone 1 to zone 4 fuel enrichment factors can be obtained as 0.635, 0.867, 1.053, and 1.393, among which the weight of the zone 3 assembly is 2 times. In order to make the axial power distribution approximate to an exponential function distribution, the axial enrichment factors are 1.41, 1.15, 1.08, 0.84, 0.76, and 0.76. Considering the neutron leakage, the axial factors of the 5th and 6th layers are set to be the same. According to the above analysis, the core fuel enrichment will reach more than 20 kinds. In order to simplify the core design, the similar enrichments are approximated by weighted average. The enrichment distribution of each fuel assembly in the core can be obtained as shown in Table 1, with a total of 6 fuel enrichments.

[0070] Table 1 Optimized fuel enrichment distribution

[0071] Axial layer / radial zone Zone 1 Zone 2 Zone 3 Zone 4 Layer 1 7.3％ 9.4％ 12.2％ 16.0％ Layer 2 7.3％ 9.4％ 12.2％ 16.0％ Layer 3 5.7％ 7.3％ 9.4％ 12.2％ Layer 4 5.7％ 7.3％ 9.4％ 12.2％ Layer 5 4.4％ 5.7％ 7.3％ 9.4％ Layer 6 4.4％ 5.7％ 7.3％ 9.4％

[0072] The core physical characteristics of the prismatic high temperature gas-cooled reactor are analyzed using a general Monte Carlo procedure.

[0073] Figure 4 This is the optimized core burnup characteristic curve. The core life is about 6800EFPD, which is 560EFPD shorter than the core life when the full reactor enrichment is 9%. This is because the core neutron leakage increases after the fuel enrichment is arranged in different zones. However, considering the 90% power factor, the optimized core life still meets the goal of 15MW thermal power and 20 years of life.

[0074] Figure 5 This is the core neutron energy spectrum diagram before and after optimization. After optimization, the core neutron energy spectrum is significantly softened, the thermal neutron fraction is significantly increased, and the fast neutron fraction is significantly reduced.

[0075] Table 2, Table 3 and Figure 6 , Figure 7It is the power distribution of the core fuel assembly at zero burnup before and after optimization. Before optimization, all fuel assemblies have the same enrichment, and the radial power peak factor is large, about 1.47; the axial power distribution is distributed in a cosine function. After optimization, the fuel assemblies are arranged in different enrichment zones according to their positions, the radial power is flattened, and the radial power peak factor is significantly reduced to about 1.18; the axial power distribution is approximately exponentially distributed as a whole; and the optimized power distribution target is basically met.

[0076] Table 2 Normalized fuel assembly power distribution at zero burnup when the core is not optimized

[0077]

[0078]

[0079] Table 3 Normalized fuel assembly power distribution at zero burnup after core optimization

[0080] Axial layer / radial zone Zone 1 Zone 2 Zone 3 Zone 4 Radial Power Crest Factor Layer 1 1.39 1.19 1.11 0.97 1.19 Layer 2 1.89 1.60 1.50 1.32 1.20 Layer 3 1.60 1.38 1.30 1.15 1.18 Layer 4 1.24 1.06 1.00 0.88 1.19 Layer 5 0.69 0.60 0.57 0.50 1.17 Layer 6 0.38 0.33 0.31 0.28 1.16 Axial power crest factor 1.58 1.56 1.56 1.55 /

[0081] When the coolant flows from top to bottom in the axial direction, the inlet temperature is 300℃ and the outlet temperature is 630℃, the average temperature distribution of the fuel in the axial direction in the core before and after the power distribution optimization is as follows: Figure 8 As shown in the figure, the axial coordinate 0m represents the axial top of the fuel active zone, and 4.2m represents the axial bottom of the fuel active zone. It can be seen that the maximum value of the average fuel temperature appears at the bottom of the fuel active zone. After the power distribution is optimized, the maximum value of the average fuel temperature is slightly reduced, about 20°C. However, considering the distribution of the maximum fuel temperature, such as Fig. 9 As shown, it can be seen that the maximum fuel temperature drops from 960°C to about 820°C, a decrease of about 140°C. The maximum fuel temperature drops significantly, which is beneficial to improving the core safety.

[0082] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these changes and variations. The above-mentioned embodiments are merely illustrative of the present invention, and the present invention may also be implemented in other specific ways or other specific forms without departing from the gist or essential features of the present invention. Therefore, the described embodiments should be considered illustrative rather than restrictive in any respect. The scope of the present invention shall be described by the appended claims, and any changes equivalent to the intent and scope of the claims shall also be included within the scope of the present invention.

Claims

1. A modular prismatic high temperature gas-cooled reactor power distribution optimization method, characterized in that: include: Determine the average enrichment, the ratio factor of the fuel assembly enrichment in each radial zone and the ratio factor of the fuel assembly enrichment in each axial layer; The enrichment of each fuel assembly is determined based on the average enrichment, the ratio factor of the enrichment of the fuel assemblies in each radial zone and the ratio factor of the enrichment of the fuel assemblies in each axial layer; Output optimization results according to the enrichment of each fuel assembly; The enrichment of each fuel assembly is determined according to the average enrichment, the ratio factor of the radial enrichment of the fuel assembly in each zone and the ratio factor of the axial enrichment of the fuel assembly in each layer according to the following formula: Cwt=Cav*Er*Ez; In the above formula, Cwt is the enrichment of each fuel assembly; Cav is the average enrichment; Er is the ratio factor of the fuel assembly enrichment in each radial zone; Ez is the enrichment ratio factor of each layer of fuel assembly in the axial direction.

2. The modular prismatic high temperature gas-cooled reactor power distribution optimization method according to claim 1, characterized in that: The method for determining the radial enrichment ratio factor of the fuel assembly in each zone is: When the fuel enrichment of the whole reactor is the same, calculate the neutron flux distribution of the radial fuel assembly in the core; The enrichment ratio factor of the fuel assemblies in each radial zone is determined according to the ratio of the inverse of the neutron flux of the fuel assemblies in each radial zone.

3. The method for optimizing power distribution of a modular prismatic high temperature gas-cooled reactor according to claim 1, characterized in that: The method for determining the enrichment ratio factor of each axial layer of fuel assembly is: The formula P(z)=C·exp(-a·z / b) is used to calculate the ratio factor of the axial fuel assembly enrichment in each layer so that the axial power distribution is approximately distributed in the form of an exponential function; In the above formula, a and b represent constants related to the coolant properties and core geometry, C is the normalization coefficient, and z represents the axial position of the core.

4. The method for optimizing power distribution of a modular prismatic high temperature gas-cooled reactor according to any one of claims 1 to 3, characterized in that: Before outputting the optimization result according to the enrichment of each fuel assembly, similar enrichment parameters are approximated to reduce the types of fuel enrichment in the entire stack.

5. The method for optimizing power distribution of a modular prismatic high temperature gas-cooled reactor according to claim 4, characterized in that: The approximate processing of similar enrichment parameters is to perform weighted average processing of similar enrichments using the number of fuel assemblies corresponding to similar enrichments as weights.

6. The modular prismatic high temperature gas-cooled reactor power distribution optimization method according to claim 4, characterized in that: The similar enrichment parameters are determined based on reducing the number of types of fuel enrichment in the entire stack to six.

Images