A method for controlling the oxygen content in a reactor coolant

Abstract

This invention provides a method for controlling the oxygen content in reactor coolant, comprising: determining the relationship between the growth thickness of the oxide layer formed on the surface of the fuel rod cladding within a preset time period under conditions of no coolant corrosion and the oxygen content in the coolant; determining the removal rate of the oxide layer on the surface of the fuel rod cladding after reaction with the coolant; determining a functional relationship between the remaining oxide layer thickness on the cladding surface and the oxygen content of the coolant under varying oxygen content conditions, based on the relationship between the oxide layer growth thickness and the oxygen content in the coolant and the oxide layer removal rate; using the functional relationship between the remaining oxide layer thickness on the cladding surface and the oxygen content of the coolant as the objective function, and determining the optimal oxygen content control strategy of the coolant corresponding to the minimum value of the remaining oxide layer thickness based on a preset optimization algorithm. This invention alleviates the oxidation and corrosion problem of fuel rod cladding materials in metallic coolants by determining the optimal oxygen content control strategy of the coolant.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor technology, and in particular to a method for controlling the oxygen content in a reactor coolant. Background Technology

[0002] The constituent elements of structural steel in nuclear systems have high solubility in liquid metal coolants (Pb / Pb-Bi). In lead-based alloy-cooled reactors (LFRs) and accelerator-driven subcritical systems (ADSs), the use of such coolants can threaten the integrity of structural components such as fuel rod cladding materials and thin-walled heat exchange tubes, affecting the safe operation of the nuclear system. Currently, one of the commonly used methods to address the corrosion problem of materials by liquid metal coolants is active oxygen control technology. This technology maintains the oxygen content in the liquid coolant through solid-phase or gas-phase oxygen control systems, allowing the oxygen in the coolant to react with the reactor structural materials to form a protective oxide layer without oxidizing the coolant constituent elements to produce solid oxide impurities. This avoids direct contact between the liquid metal and the structural materials.

[0003] The oxygen content maintained in the liquid metal coolant has a significant impact on the growth rate of the oxide layer on the surface of structural components. When the oxygen content in the liquid metal changes, the oxidative corrosion behavior of the oxide layer on the surface of the fuel rod cladding material will change. When the oxygen content in the liquid metal is high, the growth rate of the oxide layer on the surface of the reactor fuel rod cladding exceeds its corrosion rate, and the oxide layer gradually thickens during the operation of the nuclear system. Since the heat transfer capacity of the oxide layer is generally lower than that of the cladding material itself, the growth of the oxide layer leads to a decrease in the heat transfer performance of the fuel rod cladding, and an increase in the inner surface temperature of the cladding. The increase in cladding temperature, in turn, increases the outward diffusion rate of elements such as Fe and Cr from within the cladding matrix, further expanding the available space for the formation of the inner oxide layer. As the microstructure of the cladding matrix gradually changes, the oxidation rate also increases. This series of physicochemical reactions forms a positive feedback effect, and ultimately, the heat transfer deterioration caused by an excessively thick oxide layer may lead to localized burnout of the fuel rods. When the oxygen content in the liquid metal coolant is low, the temperature field inside the coolant channel shows an upward trend along the channel axis. There are significant differences in oxygen activity and oxide layer corrosion rate between the channel inlet and outlet. Near the outlet section, the local oxide layer growth rate on the fuel rod cladding surface may be lower than the corrosion rate, failing to effectively form a protective oxide layer. This leads to localized high-rate dissolution corrosion, ultimately causing fuel rod cladding damage. Therefore, controlling the oxygen content in the liquid metal coolant to achieve the optimal level to mitigate the oxidative corrosion of the fuel rod cladding is a pressing issue. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for controlling the oxygen content in reactor coolant, which can prevent damage to fuel rods from excessive or insufficient oxygen content in the coolant. This method achieves the mitigation of oxidation and corrosion problems of fuel rod cladding materials in metallic coolants through the optimal oxygen content control strategy of the coolant, and provides important reference value for reactor design and operation.

[0005] To achieve the above objectives, the technical solutions adopted in the embodiments of the present invention are as follows:

[0006] In a first aspect, embodiments of the present invention provide a method for controlling the oxygen content in a reactor coolant, comprising:

[0007] Determine the relationship between the growth thickness of the oxide layer formed on the surface of the fuel rod cladding within a preset time period under the condition that it is not corroded by the coolant and the oxygen content in the coolant;

[0008] Determine the removal rate of the oxide layer on the surface of the fuel rod cladding after it reacts with the coolant;

[0009] Based on the relationship between the growth thickness of the oxide layer and the oxygen content in the coolant, and the removal rate of the oxide layer, a functional relationship between the remaining oxide layer thickness on the surface of the cladding and the oxygen content of the coolant under varying oxygen content conditions is determined.

[0010] Using the functional relationship between the remaining oxide layer thickness on the shell surface and the oxygen content of the coolant as the objective function, the optimal oxygen content control strategy of the coolant corresponding to the minimum value of the remaining oxide layer thickness is determined based on a preset optimization algorithm; wherein, the optimal oxygen content control strategy includes the optimal oxygen content corresponding to each time period within the preset time period.

[0011] Furthermore, the present invention provides a first possible implementation of the first aspect, wherein the growth thickness of the oxide layer includes the thickness of the inner oxide layer and the growth thickness of the outer oxide layer, and the step of determining the relationship between the growth thickness of the oxide layer generated on the surface of the fuel rod cladding within a preset time period without being corroded by the coolant and the oxygen content in the coolant includes:

[0012] Based on Fick's law and the law of conservation of mass, the relationship between the growth thickness of the outer oxide layer and the oxygen content in the coolant is determined when the mass flux of metal diffusing outward from the inner oxide layer is equal to the mass flux of metal entering the outer oxide layer, provided that the cladding is not corroded by the coolant; wherein, the outer oxide layer is an oxide layer that grows outward from the surface of the cladding, and the growth thickness of the outer oxide layer varies with time.

[0013] Based on the relationship between the growth thickness of the outer oxide layer and the oxygen content in the coolant, and the metal molar concentration distribution on the shell, the relationship between the growth thickness of the inner oxide layer growing inward from the surface of the shell and the oxygen content in the coolant is determined.

[0014] The relationship between the growth thickness of the oxide layer and the oxygen content in the coolant is obtained based on the sum of the growth thickness of the outer oxide layer and the growth thickness of the inner oxide layer.

[0015] Furthermore, this embodiment of the invention provides a second possible implementation of the first aspect, wherein the removal rate of the oxide layer includes the removal rate of the inner oxide layer and the removal rate of the outer oxide layer, and the step of determining the removal rate of the oxide layer on the surface of the fuel rod cladding after reaction with the coolant includes:

[0016] Determine the corrosion rate of the oxide layer on the surface of the casing in the coolant;

[0017] The removal rate of the inner oxide layer is determined based on the corrosion rate, the density of the inner oxide layer, and the molar mass of each element in the inner oxide layer.

[0018] The removal rate of the outer oxide layer is determined based on the corrosion rate, the density of the outer oxide layer, and the molar mass of each element in the outer oxide layer.

[0019] Furthermore, the present invention provides a third possible implementation of the first aspect, wherein the step of determining the functional relationship between the remaining oxide layer thickness on the cladding surface and the oxygen content of the coolant under varying oxygen content conditions, based on the relationship between the growth thickness of the oxide layer and the oxygen content in the coolant and the removal rate of the oxide layer, includes:

[0020] The dissolution thickness of the inner oxide layer is obtained by multiplying the removal rate of the inner oxide layer by the preset time. The remaining thickness of the inner oxide layer and the oxygen content of the coolant are obtained by using the relationship between the growth thickness of the inner oxide layer and the oxygen content of the coolant, and the dissolution thickness of the inner oxide layer.

[0021] The dissolution thickness of the outer oxide layer is obtained by multiplying the removal rate of the outer oxide layer by the preset time. The remaining thickness of the outer oxide layer and the oxygen content of the coolant are obtained by using the relationship between the growth thickness of the outer oxide layer and the oxygen content of the coolant, and the dissolution thickness of the outer oxide layer.

[0022] The functional relationship between the remaining thickness of the inner oxide layer and the oxygen content of the coolant is summed with the functional relationship between the remaining thickness of the outer oxide layer and the oxygen content of the coolant to obtain the functional relationship between the remaining oxide layer thickness on the shell surface and the oxygen content of the coolant.

[0023] Furthermore, this invention provides a fourth possible implementation of the first aspect, wherein the step of determining the corrosion rate of the oxide layer on the cladding surface in the coolant includes:

[0024] When the outer oxide layer is not completely corroded, the equilibrium concentration of metal in the outer oxide layer is determined based on the equilibrium constant of the reduction reaction between the compound in the outer oxide layer and the coolant.

[0025] When the outer oxide layer is completely corroded, the equilibrium concentration of the metal in the outer oxide layer is determined based on the equilibrium constant of the reduction reaction between the compound in the inner oxide layer and the coolant.

[0026] The metal concentration on the surface of the outer oxide layer is determined based on the equilibrium concentration of the metal in the outer oxide layer and the minimum solubility of the metal in the oxide layer in the coolant.

[0027] The corrosion rate of the oxide layer on the cladding surface in the coolant is determined based on the metal concentration on the surface of the outer oxide layer and the information of the coolant.

[0028] Furthermore, this embodiment of the invention provides a fifth possible implementation of the first aspect, wherein the preset optimization algorithm includes the whale optimization algorithm.

[0029] Furthermore, this embodiment of the invention provides a sixth possible implementation of the first aspect, wherein the individual parameters of the population are generated based on a mapped chaotic sequence during population initialization in the whale optimization algorithm.

[0030] Furthermore, this embodiment of the invention provides a seventh possible implementation of the first aspect, wherein the whale optimization algorithm generates a mutant population during the annealing process based on Gaussian mutation and Cauchy mutation.

[0031] Furthermore, this embodiment of the invention provides an eighth possible implementation of the first aspect, wherein the convergence factor in the whale optimization algorithm is a nonlinear convergence factor; the formula for calculating the nonlinear convergence factor is:

[0032]

[0033] in, Let be the nonlinear convergence factor. is the initial convergence factor, iter is the current iteration number, and maxiter is the maximum iteration number.

[0034] Furthermore, the present invention provides a ninth possible implementation of the first aspect, wherein the reactor is a lead-bismuth alloy cooled reactor, the cladding material is T91 steel, and the coolant is a lead-bismuth alloy coolant.

[0035] This invention provides a method for controlling the oxygen content in a reactor coolant. The method includes: determining the relationship between the growth thickness of the oxide layer formed on the surface of the fuel rod cladding within a preset time period under conditions where it is not corroded by the coolant and the oxygen content in the coolant; determining the removal rate of the oxide layer on the surface of the fuel rod cladding after reaction with the coolant; determining a functional relationship between the remaining oxide layer thickness on the cladding surface and the oxygen content of the coolant under varying oxygen content conditions, based on the relationship between the oxide layer growth thickness and the oxygen content in the coolant and the oxide layer removal rate; using the functional relationship between the remaining oxide layer thickness on the cladding surface and the oxygen content of the coolant as the objective function, and determining the optimal oxygen content control strategy for the coolant corresponding to the minimum value of the remaining oxide layer thickness based on a preset optimization algorithm; wherein the optimal oxygen content control strategy includes the optimal oxygen content corresponding to each time period within the preset time period. This invention predicts the growth thickness and removal rate of the oxide layer on the fuel rod cladding surface under varying oxygen content conditions in the coolant. Based on the functional relationship between the remaining oxide layer thickness and the oxygen content of the coolant obtained from the growth thickness and removal rate, it determines the optimal oxygen content control strategy for each time period corresponding to the minimum remaining oxide layer thickness. This achieves dynamic regulation of the oxygen content in the coolant, maintaining the protective performance of the oxide layer and preventing damage to the fuel rods from excessively high or low oxygen content in the coolant. It mitigates the oxidation and corrosion problem of fuel rod cladding materials in metallic coolants through the optimal oxygen content control strategy, providing important reference value for reactor design and operation.

[0036] Other features and advantages of the embodiments of the present invention will be set forth in the following description, or some features and advantages may be inferred from the description or determined without doubt, or may be learned by practicing the techniques described above in the embodiments of the present invention.

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0038] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 A flowchart of a method for controlling oxygen content in a reactor coolant provided by an embodiment of the present invention is shown. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be described below in conjunction with the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0041] Significant progress has been made in the research of lead-based fast reactors. In particular, the pursuit of sustainable and efficient energy solutions has increased researchers' interest in fourth-generation reactors and accelerator-driven subcritical systems (ADS). Among potential coolant materials, lead and lead-bismuth alloys are considered candidate materials for coolants in lead-based fast reactors and ADSs due to their high boiling points, efficient heat dissipation, and inert reaction with water.

[0042] Because active oxygen content control technology can mitigate the corrosive effects of liquid metals on materials without introducing additional impurities, Pb or LBE (liquid lead-bismuth alloy coolant) experimental facilities in recent years are typically equipped with active oxygen content control systems. Currently, there are two main methods for controlling the oxygen content in liquid metals: one is to adjust the partial pressure of oxygen in the ternary gas mixture (usually water vapor, H2, and oxygen) covering the liquid metal surface using a gas-phase oxygen control system based on Henry's law and Dalton's law; the other is to utilize the mechanical stability of lead oxide (PbO) in liquid metals, using a dedicated thermal device in the solid-phase oxygen control system to achieve controlled dissolution of PbO to replenish oxygen into the liquid metal. The operable oxygen content range in nuclear systems is determined based on the thermodynamic stability of metal oxides in liquid metals.

[0043] However, the inventors discovered that in practice, when a reactor system operates at a constant oxygen concentration, two problems may arise: First, excessively high oxygen content leads to an oxide layer growth rate far exceeding its corrosion rate. As the reactor operates, the thickness of the oxide layer on the fuel rod cladding gradually increases. Since the heat transfer performance of the oxide layer is weaker than that of the cladding material itself, the temperature on the inner surface of the cladding continuously rises due to the increased thermal resistance during reactor operation. As the temperature of the inner surface increases, the outward diffusion of the constituent elements within the cladding material intensifies, leaving usable space for the growth of the inner oxide layer. When these constituent elements diffuse to the cladding surface, their reaction with oxygen further accelerates the formation of the outer oxide layer. Simultaneously, because the outer oxide layer is porous, oxygen from the liquid metal enters the usable space left by the outward diffusion of the cladding material's constituent elements through nanochannels within the outer oxide layer, further propelling oxidation into the interior of the cladding. Consequently, changes occur in the internal microstructure of the cladding, resulting in decreased mechanical properties and a shortened lifespan. This series of physicochemical reactions will create a positive feedback effect, further accelerating the growth of the oxide layer and the oxidation of the cladding substrate. Furthermore, due to the gradual increase in the temperature of the liquid metal in the vicinity along the fuel rod axis, non-uniform oxide layer growth / corrosion behavior will occur on the fuel rod cladding surface. Given the current narrow oxygen content control range, even under appropriate oxygen content conditions, the aforementioned positive feedback effect will still occur in localized areas of the fuel rod.

[0044] Secondly, when the oxygen content in the nuclear system is too low, the growth rate of the oxide layer on the surface of the fuel rod cladding is less than the corrosion rate of the oxide layer. The oxide layer originally formed on the surface of the fuel rod cladding will gradually decay and thin until the protective effect of the oxide layer disappears. When the fuel rod cladding material comes into direct contact with liquid metal, a large amount of elements such as Fe, Ni, and Cr, which have high solubility in liquid metal, will be released from the cladding material, causing dissolution corrosion of the cladding and greatly shortening the service life of the cladding.

[0045] To address the aforementioned problems, this invention provides a method for controlling oxygen content in reactor coolant, which will be described in detail below.

[0046] This embodiment provides a method for controlling the oxygen content in a reactor coolant. This method can be applied to electronic devices such as computers. See [link / reference needed]. Figure 1 The flowchart shown illustrates a method for controlling oxygen content in reactor coolant. This method mainly includes the following steps:

[0047] Step S102: Determine the relationship between the growth thickness of the oxide layer formed on the surface of the fuel rod cladding within a preset time period without being corroded by the coolant and the oxygen content in the coolant.

[0048] Without considering the corrosive effect of liquid coolant on the oxide layer on the cladding surface, a growth kinetic model of the oxide layer on the cladding surface is established based on the oxidation reaction between the cladding material and the coolant. This model includes the relationship between the thickness of the oxide layer on the cladding surface and the oxygen content in the coolant and time.

[0049] The preset duration can be the duration during which the oxygen content in the coolant needs to be controlled during reactor operation.

[0050] In one embodiment, the fuel rod cladding material provided in this example can be T91 steel, and the coolant can be liquid lead-bismuth alloy coolant. The oxidation mechanism of the T91 cladding in liquid lead-bismuth alloy coolant (LBE) can be explained by existing spatial models: iron inside the cladding migrates to the steel surface and reacts with oxygen to form a magnetite layer, leaving usable space inside the cladding for the growth of an iron-chromium spinel layer. Oxygen inside the liquid metal migrates to the internal space of the cladding through nanochannels in the outer oxide layer (magnetite layer, i.e., outer oxide layer) and diffuses and oxidizes, leading to the formation of an iron-chromium spinel oxide layer inside the cladding matrix, i.e., the inner oxide layer of the cladding.

[0051] Step S104: Determine the removal rate of the oxide layer on the surface of the fuel rod cladding after it reacts with the coolant;

[0052] Under different flow conditions, the thickness of the oxide layer formed on the cladding surface in the flowing coolant is less than that in the static coolant. This indicates that the oxide layer formed on the cladding surface itself has a certain solubility in the coolant. During the flow of the coolant, the oxide layer dissolved in the coolant will be transported to other areas along with the coolant, resulting in a concentration difference between the cladding surface and the interior of the fluid mainstream. This further generates a mass flux of dissolved substances transferred from the oxide layer to the coolant mainstream.

[0053] The removal rate of the oxide layer can be determined based on the chemical reaction relationship between the compounds in the oxide layer on the cladding surface and the coolant.

[0054] Step S106: Based on the relationship between the growth thickness of the oxide layer and the oxygen content in the coolant and the removal rate of the oxide layer, determine the functional relationship between the remaining oxide layer thickness on the cladding surface of the coolant and the oxygen content of the coolant under variable oxygen content conditions.

[0055] The oxide layer thickness in the coolant can be determined by the oxide layer removal rate and the time it takes for the oxide layer to dissolve in the coolant. Based on the difference between the growth thickness and the dissolution thickness of the oxide layer, a functional relationship between the remaining oxide layer thickness on the shell surface and the oxygen content of the coolant after a preset time can be obtained.

[0056] Step S108: The functional relationship between the remaining oxide layer thickness on the shell surface and the oxygen content of the coolant is used as the objective function. Based on a preset optimization algorithm, the optimal oxygen content control strategy of the coolant corresponding to the minimum value of the remaining oxide layer thickness is determined.

[0057] The algorithm optimizes the functional relationship between the remaining oxide layer thickness on the cladding surface and the oxygen content of the coolant using a pre-defined optimization algorithm. This minimizes the total oxidation level on the cladding surface. After multiple rounds of iterative optimization, the optimal oxygen content control strategy for the coolant is obtained, minimizing the remaining oxide layer thickness. Since the coolant oxygen content control is a dynamic, variable oxygen content control, the optimal oxygen content control strategy includes the optimal oxygen content for each time period within a preset time frame. In other words, the optimal oxygen content control strategy includes multiple oxygen content values, each representing the optimal oxygen content for the coolant at each time period within the preset time frame. The pre-defined optimization algorithm can be, for example, simulated annealing, local search, or whale optimization.

[0058] The above yields the optimal oxygen content control strategy It can be [x1, x2, ... x j [x1 is the optimal oxygen content in the first time period within the preset time limit, x2 is the optimal oxygen content in the second time period within the preset time limit, x] j The optimal oxygen content for the j-th time period within a preset duration is given by , where j is the number of time periods included within the preset duration.

[0059] By controlling the oxygen content of the coolant in different time periods, the oxidation and corrosion behavior of the oxide layer on the surface of the fuel rod cladding will change when the oxygen content in the coolant changes. By dynamically regulating the oxygen concentration, the positive feedback effect occurring in local areas of the fuel rod can be mitigated while maintaining the protective performance of the oxide layer, so as to achieve a long service life of the cladding material.

[0060] The oxygen content control method in the reactor coolant provided in this embodiment predicts the growth thickness and removal rate of the oxide layer on the surface of the fuel rod cladding under varying oxygen content conditions in the coolant. Based on the functional relationship between the remaining oxide layer thickness and the oxygen content of the coolant obtained from the growth thickness and removal rate of the oxide layer, the optimal oxygen content control strategy for each time period corresponding to the minimum remaining oxide layer thickness is determined. This achieves dynamic regulation of the oxygen content in the coolant, maintains the protective performance of the oxide layer, and avoids damage to the fuel rods due to excessively high or low oxygen content in the coolant. It mitigates the oxidation and corrosion problem of fuel rod cladding materials in metallic coolants through the optimal oxygen content control strategy of the coolant, providing important reference value for reactor design and operation.

[0061] In one embodiment, the reactor provided in this embodiment is a lead-bismuth alloy cooled reactor, the cladding material is T91 steel, and the coolant is lead-bismuth alloy coolant (LBE).

[0062] The composition information for T91 steel is shown in Table 1 below, which displays the mass percentage of each element in the T91 composition.

[0063] Table 1. Mass percentage of T91 components.

[0064] element Cr Mo Si Ni Cu Nb V Mn C P T91 9.25 0.89 0.22 0.11 0.06 0.06 0.21 0.38 0.1025 0.021

[0065] In one embodiment, the growth thickness of the oxide layer includes the thickness of the inner oxide layer and the growth thickness of the outer oxide layer. This embodiment provides an implementation method for determining the relationship between the growth thickness of the oxide layer formed on the surface of the fuel rod cladding within a preset time period and the oxygen content in the coolant, provided that the cladding is not corroded by the coolant. The specific steps are as follows:

[0066] Step (1): Based on Fick's law and the law of conservation of mass, determine the relationship between the growth thickness of the outer oxide layer and the oxygen content in the coolant when the mass flux of metal diffusing outward from the inner oxide layer is equal to the mass flux of metal entering the outer oxide layer, without being corroded by the coolant; where the outer oxide layer is the oxide layer that grows outward from the surface of the cladding, and the growth thickness of the outer oxide layer changes with time.

[0067] In calculating the oxide layer thickness, the above oxide layer growth kinetic model must satisfy the following: (i) the species concentration at the interface between the inner and outer oxide layers is constant; (ii) the Fe mass flux inside the oxide layer is constant; (iii) local thermodynamic equilibrium exists throughout the oxidation process; and (iv) the entire oxidation process is in a quasi-static equilibrium state.

[0068] After considering the above assumptions (i) to (iv), based on the calculation of the metal mass flux diffusing outward from the inner oxide layer using Fick's law, the relationship between the thickness of the outer oxide layer and time can be obtained. In addition, according to the mass conservation method, the metal flux leaving the inner oxide layer in the cladding should be equal to the metal flux entering the outer oxide layer. Based on this mass conservation information and Fick's law, another relationship between the thickness of the outer oxide layer and time can be obtained. Combining the above two relationships, the relationship between the growth thickness of the outer oxide layer and the oxygen content in the coolant can be obtained.

[0069] In one embodiment, taking T91 steel as the cladding material and lead-bismuth alloy coolant as the coolant, the oxide layer on the cladding surface includes an inner oxide layer (spinel layer) and an outer oxide layer (magnetite layer thickness). By calculating the outward diffusion of iron mass flux in the spinel layer using Fick's law, the relationship between the thickness of the magnetite layer and time can be obtained:

[0070]

[0071] Among them, h Magx represents the growth thickness of the outer oxide layer (i.e., the growth thickness of the magnetite layer), and x represents the iron-chromium spinel (Fe). 3- x Cr x The stoichiometric coefficient of Cr in O4) This represents the molar concentration of iron in the inner oxide layer. D represents the molar concentration of iron inside the casing. v D is the cation vacancy diffusion coefficient. I K is the interstitial diffusion coefficient. I The reaction constant that leads to the formation of gaps, This represents the oxygen activity coefficient at the interface between the outer and inner oxide layers. a is the oxygen activity coefficient at the interface between the inner oxide layer and the shell. I b I b V For linear regression values ​​obtained from experimental data, a is usually... i 0.18 is acceptable. Approximately 3.3 × 10 -6 , It is approximately 0.7.

[0072] According to the law of conservation of mass, the Fe flux leaving the spinel layer should be equal to the Fe flux entering the magnetite layer. Using Fick's law to calculate the Fe flux in the magnetite layer as a function of time, another relationship between the thickness of the magnetite layer and time is obtained:

[0073]

[0074] in, It represents the oxygen activity coefficient at the interface between the outer oxide layer and the coolant.

[0075] The oxygen activity coefficient at the interface between the aforementioned outer oxide layer and the coolant It can be calculated based on the following formula:

[0076]

[0077] Among them, C O (wt.%) represents the oxygen content of the coolant, M LBE M represents the molar mass of the coolant (the coolant contains 44.5 wt.% Pb and 55.5 wt.% Bi, with a molar mass of approximately 208.19 g / mol). O The molar mass of oxygen, Let be the Gibbs free energy of oxygen in the coolant, T be the temperature of the coolant, and R be the ideal gas constant. The formula for calculating the Gibbs free energy of oxygen in the coolant is:

[0078]

[0079] Oxygen activity coefficient at the interface between the cladding and the iron-chromium spinel layer It will be affected by the chemical reaction 3Fe + 2O₂ → Fe₃O₄, when When the reaction is in equilibrium, The calculation formula is:

[0080]

[0081] Among them, A fe Let ΔG be the activity coefficient of Fe in the coolant. 0 This is the standard Gibbs free energy of the reaction that forms the magnetite layer.

[0082] By combining the above formulas (1) and (2) and combining them with the above formulas (3) to (5), we can obtain the relationship between the growth thickness of the outer oxide layer (i.e., the magnetite layer) and the oxygen content in the coolant.

[0083] Step (2): Based on the relationship between the growth thickness of the outer oxide layer and the oxygen content in the coolant and the metal molar concentration distribution on the shell, determine the relationship between the growth thickness of the inner oxide layer growing from the shell surface inward and the oxygen content in the coolant;

[0084] According to the oxidation mechanism, the growth rate of the inner oxide layer is limited by the growth rate of the outer oxide layer. The growth thickness of the inner oxide layer can be calculated based on the growth thickness of the outer oxide layer and the compound type of the inner oxide layer, thus obtaining the relationship between the growth thickness of the inner oxide layer and the oxygen content in the coolant.

[0085] For example, the growth rate of the Fe-Cr spinel layer is limited by the growth rate of the magnetite layer. Therefore, there is a direct correlation between the spinel thickness and the magnetite layer thickness. The formula for calculating the growth thickness of the spinel layer is as follows:

[0086]

[0087] Among them, h sp This refers to the growth thickness of the inner oxide layer (i.e., the growth thickness of the spinel layer). This represents the molar concentration of iron in the outer oxide layer of the casing. This represents the molar concentration of iron inside the casing. This represents the molar concentration of iron in the oxide layer inside the cladding.

[0088] Step (3): Based on the sum of the growth thickness of the outer oxide layer and the growth thickness of the inner oxide layer, obtain the relationship between the growth thickness of the oxide layer and the oxygen content in the coolant.

[0089] Calculate the sum h of the growth thickness of the outer oxide layer and the growth thickness of the inner oxide layer. sp +h MagThis allows us to obtain the relationship between the growth thickness of the oxide layer and the oxygen content in the coolant.

[0090] In one embodiment, the removal rate of the oxide layer includes the removal rate of the inner oxide layer and the removal rate of the outer oxide layer. This embodiment provides an implementation method for determining the removal rate of the oxide layer on the surface of the fuel rod cladding after it reacts with the coolant. Specifically, the following steps can be followed:

[0091] Step 1): Determine the corrosion rate of the oxide layer on the cladding surface in the coolant;

[0092] The corrosion rate of the oxide layer on the cladding surface in the coolant was calculated based on the mass transfer coefficient relationship proposed by Silverman.

[0093] In one specific implementation, when the outer oxide layer is not completely corroded, the equilibrium concentration of the metal in the outer oxide layer is determined based on the equilibrium constant of the reduction reaction between the compound in the outer oxide layer and the coolant.

[0094] When the outer oxide layer is completely corroded, the equilibrium concentration of the metal in the outer oxide layer is determined based on the equilibrium constant of the reduction reaction between the compound in the inner oxide layer and the coolant.

[0095] The metal concentration on the surface of the outer oxide layer is determined based on the equilibrium concentration of the metal in the outer oxide layer and the minimum solubility of the metal in the oxide layer in the coolant.

[0096] The corrosion rate of the oxide layer on the cladding surface in the coolant is determined based on the metal concentration on the outer oxide layer surface and information about the coolant.

[0097] Taking T91 steel as the cladding material and lead-bismuth alloy coolant as an example, the formula for calculating the corrosion rate of the oxide layer in the coolant is as follows:

[0098]

[0099] Where, j Fe υ is the corrosion rate of the oxide layer in the coolant, V is the axial flow velocity of the coolant, d is the equivalent diameter of the coolant channel, and υ is the corrosion rate of the oxide layer in the coolant. -0.579 Where is the viscosity of the coolant, and D is the diffusion coefficient of iron in the coolant. The iron concentration on the surface of the outer oxide layer. This refers to the iron concentration inside the coolant.

[0100] The value is determined by the minimum value between the saturation concentration of iron in the coolant and the equilibrium concentration for the reaction, i.e.:

[0101]

[0102] in, This refers to the solubility of metallic iron in the coolant. This represents the equilibrium concentration of metallic iron in the outer oxide layer.

[0103] The solubility of Fe, Cr, and O in LBE coolant can be calculated using empirical formulas:

[0104]

[0105] in, Let represent the solubility of X in the coolant, expressed in wt.% (unit of solubility). X can be Fe, Cr, or O. For Fe, coefficient A is 2.00 and B is -4399; for Cr, coefficient A is 1.12 and B is -3056; for O, coefficient A is 2.25 and B is 4125.

[0106] When the outer oxide layer is not completely corroded, the equilibrium constant of the reduction reaction of the magnetite layer in the liquid lead-bismuth eutectic (Fe3O4(s) + 4Pb(l) → 3Fe(l) + 4PbO) is calculated as follows:

[0107]

[0108] Among them, K eq C is the equilibrium constant. O This refers to the oxygen content in the coolant. The solubility of oxygen in the coolant. This represents the equilibrium concentration of iron in the outer oxide layer. Let T be the solubility of iron in the coolant, and a be the temperature of the coolant. Pb Let be the activity of lead in the coolant, R be the ideal gas constant, and ΔG be the value of lead. PbO The formation Gibbs free energy of PbO, The Gibbs free energy for the formation of Fe3O4 is given.

[0109] The equilibrium concentration of iron in the outer oxide layer can be derived from the above formula (10). The expression is:

[0110]

[0111] The formula for calculating the activity of lead in coolant is:

[0112] a Pb =χ Pb exp[-(1-χ Pb ) 2 (0.2+447 / T)] (12)

[0113] Where, χ Pb denoted as Pb mass fraction in the coolant, and T as coolant temperature.

[0114] When the outer oxide layer has completely corroded, the spinel layer comes into contact with the coolant and a chemical reaction occurs: Fe 3-x Cr x O4(s) + 4Pb(l) → (3-x)Fe(l) + xCr(l) + 4PbO. The equilibrium constant for this chemical reaction is calculated using the following formula:

[0115]

[0116] Among them, C Cr The Cr content in the coolant. Let ΔG be the solubility of Cr in the coolant. Sp This represents the Gibbs free energy for the formation of the spinel layer. Based on the above formula (13), the equilibrium concentration of iron in the outer oxide layer when the outer oxide layer is completely corroded can be derived. The expression.

[0117] The formula for calculating the Gibbs free energy of formation of the main oxides in the coolant is:

[0118] ΔG=ΔH-T·ΔS (14)

[0119] Within the temperature range of 400-1000K, the values ​​of enthalpy and entropy involved in the above formula can be found in Table 2 below, which shows the values ​​of the free enthalpy coefficients of the main oxides.

[0120] Table 2. Values ​​of Free Enthalpy Coefficients of Major Oxides

[0121] Chemical reaction ΔH / (kJ / mol) ΔS / (kJ / mol / K) <![CDATA[Pb+1 / 2O2→PbO]]> -218.805 -0.09955 <![CDATA[3Fe+2O2→Fe3O4]]> -1103.980 -0.31380 <![CDATA[Fe+1 / 2O2→FeO]]> -264.595 -0.06570 <![CDATA[2Fe+3 / 2O2→Fe2O3]]> -816.195 -0.23535 <![CDATA[2Cr+3 / 2O2→Cr2O3]]> -1133.115 -0.25770

[0122] Step 2): Determine the removal rate of the inner oxide layer based on the corrosion rate, the density of the inner oxide layer, and the molar mass of each element in the inner oxide layer;

[0123] Taking T91 steel as the cladding material and lead-bismuth alloy coolant as an example, the formula for calculating the removal rate of the inner oxide layer is:

[0124]

[0125] Where, k rem,sp J represents the removal rate of the inner oxide layer (m / s). Fe For corrosion rate, M represents the density of the inner oxide layer. Fe M is the molar mass of iron. Cr M is the molar mass of Cr. O denoted as , where is the molar mass of oxygen, and x is the stoichiometric ratio of Cr in the inner oxide layer.

[0126] Step 3): Determine the removal rate of the outer oxide layer based on the corrosion rate, the density of the outer oxide layer, and the molar mass of each element in the outer oxide layer.

[0127] Taking T91 steel as the cladding material and lead-bismuth alloy coolant as an example, the formula for calculating the removal rate of the outer oxide layer is:

[0128]

[0129] Among them, K rem,mag The removal rate of the outer oxide layer (m / s) This represents the density of the outer oxide layer.

[0130] In one embodiment, this embodiment provides a specific implementation method for determining the functional relationship between the remaining oxide layer thickness on the cladding surface and the oxygen content of the coolant under varying oxygen content conditions, based on the relationship between the oxide layer growth thickness and the oxygen content in the coolant, and the oxide layer removal rate:

[0131] The dissolution thickness t·K of the inner oxide layer is obtained by multiplying the removal rate of the inner oxide layer by the preset time. rem,sp Based on the relationship between the growth thickness of the inner oxide layer and the oxygen content in the coolant, and the dissolution thickness of the inner oxide layer, a functional relationship between the remaining thickness of the inner oxide layer and the oxygen content in the coolant is obtained.

[0132] After time t, the formula for calculating the remaining thickness of the inner oxide layer is:

[0133] h sp,remain =h Sp -t·K rem,sp (17)

[0134] The growth thickness h of the inner oxide layer obtained above sp Substituting the relationship between the oxygen content of the coolant and the oxygen content of the coolant into formula (17), we can obtain the functional relationship between the remaining thickness of the inner oxide layer and the oxygen content of the coolant.

[0135] The dissolution thickness t·K of the outer oxide layer is obtained by multiplying the removal rate of the outer oxide layer by the preset time. rem,mag Based on the relationship between the growth thickness of the outer oxide layer and the oxygen content in the coolant, and the dissolution thickness of the outer oxide layer, a functional relationship between the remaining thickness of the outer oxide layer and the oxygen content in the coolant is obtained.

[0136] After time t, the formula for calculating the remaining thickness of the outer oxide layer is:

[0137] h mag,remain =h Mag -t·K rem,mag (18)

[0138] The growth thickness h of the outer oxide layer obtained above Mag Substituting the relationship between the oxygen content of the coolant and the remaining thickness of the outer oxide layer into formula (18), we can obtain the functional relationship between the oxygen content of the coolant and the remaining thickness of the outer oxide layer.

[0139] The functional relationship between the remaining thickness of the inner oxide layer and the oxygen content of the coolant is summed with the functional relationship between the remaining thickness of the outer oxide layer and the oxygen content of the coolant to obtain the functional relationship between the remaining oxide layer thickness on the shell surface and the oxygen content of the coolant.

[0140] The objective function of the above-mentioned preset optimization algorithm is:

[0141]

[0142] in, Let the oxygen content vector include the oxygen content corresponding to each time period. After performing i rounds of iterative optimization calculations on the above objective function based on a preset optimization algorithm, the optimal oxygen content control strategy can be obtained.

[0143] During the optimization calculation process, the optimal oxygen content control strategy obtained must satisfy the condition that the remaining thickness h of the oxide layer at any given time is... sp,remain All are greater than 0 μm, meaning the constraint function for the above objective function is:

[0144] h sp,remain,i >0 (20)

[0145] In one embodiment, when the casing is made of other materials, the Fe and its corresponding oxides and chemical reaction formulas in the above formulas are changed accordingly. When the coolant is made of other materials, the Pb and its corresponding oxides and chemical reaction formulas in the above formulas are also changed accordingly.

[0146] In one embodiment, the preset optimization algorithm provided in this embodiment is the whale optimization algorithm.

[0147] The whale optimization algorithm is a heuristic optimization algorithm based on the behavior of whale groups. Its main idea is to simulate the behavior of whale groups at different stages:

[0148] Search and hunting behavior: When searching for food, whales swim "forward" to find prey. In the algorithm, "forward" corresponds to the current optimal solution, pointing to the possible best solution.

[0149] Randomness: Whales use random swimming when foraging, which is simulated as a certain degree of randomness in the algorithm, allowing the algorithm to search more extensively in the solution space.

[0150] Social behavior: Some whales form social groups and cooperate to forage. Similarly, in algorithms, some individuals will adopt a group approach and improve their search strategies through cooperation.

[0151] By simulating these behaviors of whales to optimize the solution space, global optimization is facilitated, while also exhibiting high convergence speed and search efficiency. The specific implementation of the whale optimization algorithm includes steps such as updating the whale's position, exploring the search space, and optimizing the objective function.

[0152] The optimization algorithm for whale behavior at different stages mainly includes three different mechanisms: (1) shrinking encirclement mechanism; (2) shrinking foraging mechanism; and (3) spiral mechanism.

[0153] The shrinking encirclement mechanism primarily simulates the behavior of whale groups hunting prey. The whales swim around the expected target "prey" (optimal solution), a process that helps the algorithm quickly search the solution space and adjust the solution near the target.

[0154]

[0155] in, This is the updated position vector of the individual. This is the position vector of the best individual in the whale population before the update. The position vector of the individual before the update. and For the control coefficient vector, and The calculation formula is:

[0156]

[0157]

[0158] in, It is a random vector distributed between [0, 1]; This is the convergence factor vector, which decreases linearly from 2 to 0 as the number of iterations increases in the whale optimization algorithm.

[0159] The search-foraging mechanism simulates the behavior of whales searching for food, attempting to find better solutions through a random search strategy. This aims to increase the diversity of the algorithm and thus better explore the solution space.

[0160]

[0161] in, This is the position vector of a random individual in the whale population before the update. Let be the distance vector between the current whale's position vector and a randomly selected whale.

[0162] In the later stages of the algorithm, the spiral mechanism uses a function of logarithmic spiral shape to adjust the search strategy to explore the solution space more accurately:

[0163]

[0164] in, Let be the distance vector between the current whale and the whale at the optimal position, b be a constant coefficient that determines the spiral shape of the whale as it spirals forward, and l be a random number between [-1, 1].

[0165] The updated position vector of each individual obtained in each round is input into the above objective function, and then the remaining oxide layer thickness on the shell surface is updated accordingly until the number of iterations reaches the preset number of iterations, so as to obtain the optimal oxygen content control strategy corresponding to the minimum value of the remaining oxide layer thickness on the shell surface.

[0166] Considering the following problems that the current whale optimization algorithm exhibits when performing optimization search for oxygen control strategies in lead-bismuth fast reactors: Problem (1) When the number of individuals in the random uniform initialization population method is small, inefficient search problems arise due to randomness. Problem (2) Due to the setting of more discrete time nodes, the problem dimension increases, resulting in poor performance of the algorithm's global search capability even when optimizing within a narrow oxygen content control range. Problem (3) The oxygen control strategy obtained under the corresponding constraints still cannot significantly improve the oxidation problem of the cladding matrix, indicating that the algorithm's local development capability still needs to be improved.

[0167] To address the aforementioned issues, this embodiment adjusts and improves the whale optimization algorithm itself.

[0168] In one embodiment, the whale optimization algorithm provided in this embodiment generates individual parameters of the population based on a mapped chaotic sequence during population initialization.

[0169] To address the aforementioned problem (1), a chaotic mapping back-learning population merging method was adopted to replace the random uniform initialization of the population in the original whale optimization algorithm. By generating individual population parameters through a chaotic sequence generated by the Tent mapping, the number of individuals in the population can be distributed as evenly as possible in the global solution space, even when the number is small. The fixed-point problem inherent in the Tent mapping is addressed by adding a small perturbation at the tail. For a random number x randomly generated between (0,1)... i The Tent chaotic mapping is expressed by the following two equations for x. i After performing chaos transformation, the chaos number x can be obtained. i+1 :

[0170] xi <0.5,x i+1 =2×x i +U(-1,1) / N (26)

[0171] x i ≥0.5,x i+1 =2×(1-x) i )+U(-1,1) / N (27)

[0172] random number x i After being processed by chaos reduction, it becomes x. i+1 N is the number of data points in the generated sequence, and U is the uniform distribution function.

[0173] In one embodiment, the whale optimization algorithm provided in this embodiment generates a mutant population during the annealing process based on Gaussian mutation and Cauchy mutation.

[0174] To address the aforementioned problem (2), considering the randomness and acceptance of poor solutions inherent in simulated annealing, which helps avoid getting trapped in local optima and has advantages in solving complex problems such as combinatorial optimization and parameter optimization, especially in finding the global optimum or near-optimal solution for large-scale problems, the idea of ​​simulated annealing can be integrated into the whale optimization algorithm to enhance its global search capability and strengthen its ability to escape local optima. The state transition operation in simulated annealing and the random acceptance of poor solutions are used to preserve population diversity. For state transition, a combination of Gaussian and Cauchy mutations is used to generate the mutated population during the annealing process:

[0175]

[0176] in, To simulate the variant individuals generated during the annealing process. Individuals generated by Gaussian mutation. For individuals generated by Cauchy mutation, iter is the current iteration number, and maxiter is the maximum iteration number set by the algorithm. As can be seen from the above formula (28), the weight of Cauchy mutation is relatively high in the early stage of iteration. A larger step size can be obtained through Cauchy mutation, which can avoid the algorithm from getting trapped in a local optimum. As the algorithm continues to run, the weight of Gaussian mutation gradually increases. The outstanding local search capability of Gaussian mutation enables the candidate solution to be accurately searched in the local range, thereby improving the optimization accuracy of the algorithm.

[0177] After each iteration in the original whale optimization algorithm, a new group of mutated whales is generated by the state transition in simulated annealing. The fitness between the original whale group and the mutated whale group is evaluated, and poor whale individuals are accepted with a certain probability. A new population is generated by population fusion, which includes individuals from both the original whale group and the mutated whale group. In the next iteration, iterative calculations are performed based on the new population obtained by fusion.

[0178] In one embodiment, the convergence factor in the whale optimization algorithm provided in this embodiment is a nonlinear convergence factor; the formula for calculating the nonlinear convergence factor is:

[0179]

[0180] in, It is a nonlinear convergence factor. is the initial convergence factor, iter is the current iteration number, and maxiter is the maximum iteration number.

[0181] To address the aforementioned problem (3), the convergence factor... The changes made to the whale optimization algorithm primarily involve both global exploration and local exploitation. Related, and parameters Mainly affected by the convergence factor The convergence factor is controlled by [the factor]. It plays a crucial role in the convergence speed and search accuracy of the algorithm. When When the value is large, the algorithm has strong global search capabilities and is prone to escaping local optima, but its local exploitation ability is weak, leading to a decrease in convergence speed. Conversely, if... A smaller convergence factor results in stronger local optimization capabilities and faster convergence speed, but it is also more prone to getting trapped in local optima. The linear convergence factor in the original whale optimization algorithm compromises its global search capability in the early stages and reduces the precision of its local optimization capabilities in the later stages. Therefore, a nonlinear convergence factor is used instead of the original linear convergence factor. The use of the nonlinear factor ensures that the convergence factor in the early stages of the algorithm is greater than that in the original whale optimization algorithm, resulting in a stronger global search capability; while in the later stages, the convergence factor is smaller than that in the original whale optimization algorithm, improving the algorithm's local optimization capabilities and increasing its accuracy.

[0182] The oxygen content control method in the reactor coolant provided in this embodiment analyzes the growth / corrosion of the oxide layer on the cladding surface under varying oxygen concentration conditions using an oxidation corrosion model of the fuel rod cladding material. Simultaneously, it combines a fusion-simulated annealing variant chaotic whale optimization algorithm to optimize the oxygen content control strategy for lead-bismuth fast reactor operation. By employing the optimized oxygen control strategy, the oxidation corrosion problem of the fuel rod cladding material caused by the liquid metal coolant is mitigated. A fusion-simulated annealing variant chaotic whale oxygen control strategy optimization model is constructed, improving the safety and reliability of the reactor.

[0183] This invention provides an electronic device, which includes a processor and a memory. The memory stores a computer program that can run on the processor. When the processor executes the computer program, it implements the steps of the method provided in the above embodiments.

[0184] This invention provides a computer-readable medium storing computer-executable instructions. When these computer-executable instructions are invoked and executed by a processor, they cause the processor to implement the methods described in the above embodiments.

[0185] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working process of the system described above can be referred to the corresponding process in the foregoing embodiments, and will not be repeated here.

[0186] Furthermore, in the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances.

[0187] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0188] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0189] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method of controlling the oxygen content in a reactor coolant, characterized by, The method comprises the following steps: determining a relationship between the growth thickness of the oxide layer on the surface of the fuel rod cladding and the oxygen content in the coolant under the condition that the surface of the fuel rod cladding is not corroded by the coolant within a preset time period; determining the removal rate of the oxide layer on the surface of the fuel rod cladding after the oxide layer reacts with the coolant; determining a functional relationship between the residual oxide layer thickness on the surface of the cladding and the oxygen content in the coolant under the condition that the oxygen content in the coolant changes based on the relationship between the growth thickness of the oxide layer and the oxygen content in the coolant and the removal rate of the oxide layer; taking the functional relationship between the residual oxide layer thickness on the surface of the cladding and the oxygen content in the coolant as a target function, and determining an optimal oxygen content control strategy of the coolant corresponding to the minimum residual oxide layer thickness based on a preset optimization algorithm; wherein the optimal oxygen content control strategy comprises optimal oxygen contents corresponding to each time period within the preset time period.

2. The method of claim 1, wherein, The growth thickness of the oxide layer comprises the thickness of the inner oxide layer and the growth thickness of the outer oxide layer, and the step of determining the relationship between the growth thickness of the oxide layer on the surface of the fuel rod cladding and the oxygen content in the coolant under the condition that the surface of the fuel rod cladding is not corroded by the coolant within a preset time period comprises the following steps: determining the relationship between the growth thickness of the outer oxide layer and the oxygen content in the coolant based on Fick's law and mass conservation under the condition that the surface of the cladding is not corroded by the coolant, wherein the metal mass flux of the inner oxide layer diffusing outward is equal to the metal mass flux entering the outer oxide layer, and the outer oxide layer is the oxide layer growing outward from the surface of the cladding, and the growth thickness of the outer oxide layer changes with time; determining the relationship between the growth thickness of the inner oxide layer growing inward from the surface of the cladding and the oxygen content in the coolant based on the relationship between the growth thickness of the outer oxide layer and the oxygen content in the coolant and the molar concentration distribution of the metal on the cladding; obtaining the relationship between the growth thickness of the oxide layer and the oxygen content in the coolant based on the sum of the growth thickness of the outer oxide layer and the growth thickness of the inner oxide layer.

3. The method of claim 2, wherein, The removal rate of the oxide layer comprises the removal rate of the inner oxide layer and the removal rate of the outer oxide layer, and the step of determining the removal rate of the oxide layer on the surface of the fuel rod cladding after the oxide layer reacts with the coolant comprises the following steps: determining the corrosion rate of the oxide layer on the surface of the cladding in the coolant; determining the removal rate of the inner oxide layer based on the corrosion rate, the density of the inner oxide layer, and the molar mass of each element in the inner oxide layer; determining the removal rate of the outer oxide layer based on the corrosion rate, the density of the outer oxide layer, and the molar mass of each element in the outer oxide layer.

4. The method of claim 3, wherein, The step of determining a functional relationship between the residual oxide layer thickness on the surface of the cladding and the oxygen content in the coolant under the condition that the oxygen content in the coolant changes based on the relationship between the growth thickness of the oxide layer and the oxygen content in the coolant and the removal rate of the oxide layer comprises the following steps: The dissolution thickness of the inner oxide layer is obtained based on the product of the removal rate of the inner oxide layer and the preset time length, and the functional relationship between the residual thickness of the inner oxide layer and the oxygen content of the coolant is obtained based on the relationship between the growth thickness of the inner oxide layer and the oxygen content in the coolant and the dissolution thickness of the inner oxide layer. The dissolution thickness of the outer oxide layer is obtained based on the product of the removal rate of the outer oxide layer and the preset time length, and the functional relationship between the residual thickness of the outer oxide layer and the oxygen content of the coolant is obtained based on the relationship between the growth thickness of the outer oxide layer and the oxygen content in the coolant and the dissolution thickness of the outer oxide layer. The functional relationship between the residual thickness of the outer oxide layer and the oxygen content of the coolant is obtained by adding the functional relationship between the residual thickness of the inner oxide layer and the oxygen content of the coolant and the functional relationship between the residual thickness of the outer oxide layer and the oxygen content of the coolant.

5. The method of claim 3, wherein, The step of determining the corrosion rate of the oxide layer on the cladding surface in the coolant comprises: When the outer oxide layer is not completely corroded, the equilibrium concentration of metal in the outer oxide layer is determined based on the equilibrium constant when the compound of the outer oxide layer is reduced in the coolant; When the outer oxide layer is completely corroded, the equilibrium concentration of metal in the outer oxide layer is determined based on the equilibrium constant when the compound of the inner oxide layer is reduced in the coolant; The metal concentration on the surface of the outer oxide layer is determined based on the equilibrium concentration of metal in the outer oxide layer and the minimum value of the solubility of the metal in the coolant; The corrosion rate of the oxide layer on the cladding surface in the coolant is determined based on the metal concentration on the surface of the outer oxide layer and the information of the coolant.

6. The method of claim 1, wherein, The preset optimization algorithm comprises a whale optimization algorithm.

7. The method of claim 6, wherein, In the whale optimization algorithm, the population initialization is based on a mapping chaotic sequence to generate population individual parameters.

8. The method of claim 6, wherein, In the whale optimization algorithm, a mutation population in the annealing process is generated based on Gaussian mutation and Cauchy mutation.

9. The method of claim 6, wherein, The convergence factor in the whale optimization algorithm is a nonlinear convergence factor, and the calculation formula of the nonlinear convergence factor is: wherein, is the non-linear convergence factor, is the initial convergence factor, iter is the current iteration number, and maxiter is the maximum iteration number.

10. The method according to any one of claims 1 to 9, characterized in that, The reactor is a lead-bismuth alloy cooled reactor, the cladding material is T91 steel, and the coolant is a lead-bismuth alloy coolant.

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