Method for predicting boron distribution in corrosion product deposit layers based on variable porosity

Abstract

A method for predicting boron distribution in corrosion product deposits based on variable porosity is proposed. This method constructs the adsorption equilibrium of boron within the deposit layer through adsorption kinetics, obtaining the dynamically changing porosity of the corrosion product deposit layer. Transport equations for boron convection, diffusion, adsorption, and precipitation are then established. A mathematical model of boron transport coupled with chemical reactions based on dynamic variable porosity is obtained by discretization using the finite volume method. The model is iteratively solved to obtain the boron distribution under dynamic variable porosity in the corrosion product deposit layer. This invention can realize variable porosity during the boron precipitation process within the corrosion product layer and accurately predict the boron concentration distribution under variable porosity caused by boron precipitation in the corrosion product deposit layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of reactor control, and particularly relates to a boron distribution prediction method for a corrosion product deposition layer based on variable porosity. BACKGROUND

[0002] The migration and distribution of boron elements in the corrosion product deposition layer is a process involving flow, heat transfer, mass transfer and chemical reaction, and the precipitation behavior of boron elements in the dirt can cause significant changes in the local porosity of the dirt, but the existing technology cannot accurately predict the boron concentration distribution under the variable porosity of the corrosion product deposition layer caused by boron precipitation. SUMMARY

[0003] The present application is aimed at the defects in the prior art that the existing technology for predicting the internal corrosion product deposition layer involving multiple physical phenomena such as flow, heat transfer, mass transfer and chemical reaction is based on the fixed porosity modeling of the corrosion product deposition layer, cannot reflect the influence of the change of the deposition layer porosity caused by the precipitation of boron elements on the multiple physical phenomena, cannot make feedback to the porosity evolution driven by precipitation, and cannot realize the real and effective boron distribution prediction of the corrosion product deposition layer under the influence of precipitation.

[0004] The present application is achieved by the following technical solutions:

[0005] The present application relates to a boron distribution prediction method for a corrosion product deposition layer based on variable porosity, comprising:

[0006] Step 1: Construct the adsorption equilibrium of boron in the deposition layer by adsorption kinetics to obtain the dynamically changing porosity of the corrosion product deposition layer.

[0007] Step 2: Establish the transport equation of boron convection, diffusion, adsorption and precipitation, and obtain the boron transport coupling chemical reaction mathematical model based on dynamic variable porosity by finite volume method.

[0008] Step 3: Iteratively solve the boron transport coupling chemical reaction mathematical model to obtain the boron distribution under the dynamic variable porosity of the corrosion product deposition layer.

[0009] This invention relates to a boron distribution prediction system for corrosion product deposits based on variable porosity, which implements the above-mentioned method. The system includes: an adsorption modeling unit, a transport equation construction unit, a numerical discretization unit, and a distribution prediction unit. Specifically: the adsorption modeling unit establishes an adsorption kinetic model based on the adsorption characteristics of boron in the corrosion product deposit layer, performs boron-zinc adsorption calculations and analysis, and obtains boron-zinc adsorption distribution data for the deposit layer; the transport equation construction unit constructs a boron transport coupled chemical reaction control equation that includes convection, diffusion, adsorption, and precipitation processes based on adsorption parameters; the numerical discretization unit discretizes the coupled equations using the finite volume method to form a multi-field coupled mathematical model suitable for numerical solution; and the distribution prediction unit iteratively solves the mathematical model to obtain the spatial distribution of boron in the corrosion product deposit layer under dynamic porosity evolution.

[0010] Technical effect

[0011] The present invention establishes a boron convection-diffusion-reaction-adsorption-precipitation coupled model and introduces the porosity of the corrosion product deposit layer as a dynamic evolution variable into the boron transport model. By reversing the pore structure field through adsorption and precipitation behavior, it achieves accurate identification of boron migration behavior driven by pore evolution. Compared with the prior art, the present invention can predict boron migration distribution with more accurate physical consistency and spatial resolution, which can be used to guide the analysis of boron distribution in the fouling of pressurized water reactors from startup to shutdown. Attached Figure Description

[0012] Figure 1 This is a schematic diagram / flowchart of the invention.

[0013] Figure 2 This is a diagram of a mass transfer and transport coupled chemical reaction model based on dynamic variable porosity.

[0014] Figure 3 This is a rendering of an example.

[0015] Figure: Spatiotemporal distribution of boron concentration inside the sediment layer under typical pressurized water reactor operating conditions (left) t=0s, porosity=60.0% (right) t=1200s, porosity=58.5%. Detailed Implementation

[0016] like Figure 1 As shown, this embodiment relates to a method for predicting the boron distribution in corrosion product deposits based on variable porosity, including:

[0017] Step 1: Construct a dynamically changing porosity model for the corrosion product deposit layer, specifically including:

[0018] 1.1 The boron element in the corrosion product deposition layer is precipitated and adsorbed on the porous skeleton of the deposition layer, changing the porosity of the corrosion product deposition layer, and the adsorption reaction of boron in the deposition layer is described as According to the Langmuir-Fruendlich assumption, the kinetic equation of the reaction is The adsorption equilibrium of boron in the deposition layer under ideal conditions is obtained, wherein: is the average number of adsorption sites required for one boric acid, is the net adsorption rate of boron, and are the adsorption reaction rate constant and the desorption reaction rate constant of boron, respectively, and the two parameters are independent of each other and only related to the element type, deposition layer structure, pH and temperature conditions, is the boron concentration, and are the density of the adsorbed site and the maximum adsorption site density, respectively.

[0019] 1.2 Since the adsorption and reaction of boron will interact with each other, taking the displacement of Ni by boron in the adsorbed site of the deposition layer as an example, the competitive adsorption satisfies The reaction rate of competitive adsorption is Since the reaction is a reversible process, the displacement reaction is a reversible reaction, and the equilibrium constant of the competitive adsorption reaction of boron in the deposition layer can be obtained, wherein: The rate of the competitive reaction of boron displacing Ni can be calculated according to the difference in the distribution of boron / Ni elements in the deposition layer measured by the corrosion product deposition and boron migration experiment, and are the adsorption reaction rate constant and the desorption reaction rate constant of the competitive reaction of boron displacing Ni, respectively.

[0020] 1.3 From the self-adsorption equilibrium and the competitive adsorption equilibrium, the adsorption rate of Ni and boron when they exist simultaneously in the deposition layer is obtained .

[0021] Step two, according to the adsorption rate obtained in step one, the transport equation of boron convection, diffusion, adsorption and precipitation is established, and the finite volume method is used for discretization to form a mass transfer transport coupling chemical reaction model based on dynamic variable porosity as shown in Figure 2 , which specifically includes:

[0022] 2.1 The temperature control equation in the deposition layer is obtained by the energy conservation method , and the flow equation of the coolant in the deposition layer is obtained by Darcy's law , wherein: is the coolant density, is the constant pressure specific heat capacity of the coolant, temperature, the total thermal conductivity of the deposit layer weighted by the solid component and the coolant based on the fractal theory, the Darcy flow velocity of the coolant in the deposit layer, and the volume change caused by boron adsorption and boron precipitation, respectively.

[0023] 2.2 The time-space distribution expression of the concentration in the deposit layer mainly affected by the convection diffusion, boron adsorption and boron precipitation considering the ionization of water, the hydrolysis of boric acid, the precipitation of boron-lithium compound and the iron-nickel oxide reaction is as follows: wherein the concentration change caused by the convection diffusion the concentration change caused by the chemical reaction the concentration change caused by the adsorption wherein: is the solute diffusion coefficient, is the solute charge number, is the Faraday constant, is the ideal gas constant, is the coolant temperature, is the potential difference caused by the convection diffusion, is the net rate of the solute generated by the chemical reaction.

[0024] Step three, as shown in Figure 3 , the mass transfer transport coupling chemical reaction model constructed in step two is discretely processed by using the finite volume method, and then the boron transport coupling chemical reaction mathematical model based on the dynamic variable porosity is iteratively solved to obtain the boron distribution under the dynamic variable porosity of the corrosion product deposit layer, specifically as follows: wherein: and are the total volume of the deposit layer and the volume of the solid skeleton in the deposit layer, respectively.

[0025] Step four, steps one to three are repeated until the required analysis time is reached.

[0026] Compared with the prior art, the porosity of the corrosion product deposit layer is introduced into the boron transport model as a dynamic evolution variable in the present application, so that the boron migration distribution prediction is more physically information real.

[0027] The above specific embodiments can be adjusted in different ways by those skilled in the art without departing from the principles and purposes of the present application, and the protection scope of the present application is subject to the claims and is not limited by the above specific embodiments, and each implementation scheme within the scope is subject to the constraint of the present application.

Claims

1. A method for predicting boron distribution in corrosion product deposits based on variable porosity, characterized in that, include: Step 1: Construct a model of the porosity of the corrosion product deposit layer by means of the adsorption kinetics to obtain the porosity of the corrosion product deposit layer. Step 2: Establish transport equations for boron convection, diffusion, adsorption, and precipitation, and obtain a mathematical model of boron transport coupled with chemical reaction based on dynamic variable porosity by discretization using the finite volume method. The boron transport coupled chemical reaction mathematical model is constructed in the following way: 2.1 The temperature control equation inside the sedimentary layer is obtained using the energy conservation method. The flow equation of the coolant inside the deposition layer was obtained using Darcy's law. ,in: Coolant density, The specific heat capacity of coolant at constant pressure temperature, The overall thermal conductivity of the sedimentary layer is obtained by weighting the solid composition and coolant within the sedimentary layer based on fractal theory. Darcy velocity of coolant within the deposition layer and The volume changes are caused by boron adsorption and boron precipitation, respectively. 2.2 The boron transport coupled chemical reaction process within the sedimentary layer is mainly affected by convection diffusion, boron adsorption, and boron precipitation. Considering water ionization, boric acid hydrolysis, precipitation of boron-lithium compounds, and the reaction of iron-nickel oxides, the spatiotemporal distribution expression of boron concentration within the sedimentary layer is as follows: Among them: concentration changes caused by convection diffusion Concentration changes caused by chemical reactions Concentration changes caused by adsorption ,in: The solute diffusion coefficient is... The solute charge number It is Faraday's constant. Let be the ideal gas constant. This refers to the coolant temperature. This is due to the potential difference caused by convection and diffusion. The net rate at which solute is produced in a chemical reaction; Step 3: Iteratively solve the mathematical model of boron transport coupled with chemical reaction to obtain the boron distribution under dynamic variable porosity of the corrosion product deposit layer.

2. The method for predicting boron distribution in corrosion product deposits based on variable porosity according to claim 1, characterized in that, The dynamically changing porosity model of the corrosion product deposit layer is obtained in the following way: 1.1 Using the corrosion product deposit layer as a porous framework, boron is precipitated and adsorbed within the deposit layer, altering the porosity of the corrosion product deposit layer. The adsorption reaction of boron within the deposit layer is described as follows: According to the Langmuir-Fruendlich hypothesis, the kinetic equation for the reaction is: The adsorption equilibrium of boron within the deposition layer under ideal conditions was obtained, wherein: This represents the average number of adsorption sites required for boric acid. This represents the net adsorption rate of boron. and These are the rate constants for boron adsorption and desorption, respectively. These two parameters are independent of each other and depend only on the element type, deposition layer structure, pH, and temperature conditions. For boron concentration, and These represent the density of the already adsorbed sites and the density of the maximum adsorption site, respectively. 1.2 Due to the mutual influence between boron adsorption and reaction, taking the replacement of Ni at the adsorption sites of boron in the deposition layer as an example, competitive adsorption satisfies... The rate of competitive adsorption Since the reaction is a reversible process, and the isomorphic substitution reaction is reversible, the equilibrium constant of the boron competitive adsorption reaction within the deposition layer can be obtained, where: The rate of the competing reaction of boron replacing Ni can be estimated from the difference in boron / Ni elemental distribution within the deposited layer as measured by corrosion product deposition and boron migration experiments. and These are the adsorption rate constant and desorption rate constant of the competing reaction of boron replacing Ni, respectively; 1.3 From the self-adsorption equilibrium and competitive adsorption equilibrium, the adsorption rates of Ni and boron in the presence of both in the deposition layer are obtained. .

3. The method for predicting boron distribution in corrosion product deposits based on variable porosity according to claim 1, characterized in that, The iterative solution refers to: discretizing the mass transfer and transport coupled chemical reaction model constructed in step two using the finite volume method, and then iteratively solving the resulting boron transport coupled chemical reaction mathematical model based on dynamic variable porosity to obtain the boron distribution under dynamic variable porosity in the corrosion product deposition layer, specifically: ,in: and These represent the total volume of the sedimentary layer and the volume of the solid skeleton within the sedimentary layer, respectively. The iterative solution involves repeating steps one through three until the desired analysis time is reached.

4. A system for predicting boron distribution in corrosion product deposits based on variable porosity, implementing the method of any one of claims 1-3, characterized in that, include: The system comprises an adsorption modeling unit, a transport equation construction unit, a numerical discretization unit, and a distribution prediction unit. Specifically: the adsorption modeling unit establishes an adsorption kinetic model based on the adsorption characteristics of boron in the corrosion product deposit layer, performs boron-zinc adsorption calculations and analysis, and obtains boron-zinc adsorption distribution data for the deposit layer; the transport equation construction unit constructs a boron transport coupled chemical reaction governing equation that includes convection, diffusion, adsorption, and precipitation processes based on adsorption parameters; the numerical discretization unit discretizes the coupled equations using the finite volume method to form a multi-field coupled mathematical model suitable for numerical solutions; and the distribution prediction unit iteratively solves the mathematical model to obtain the spatial distribution of boron in the corrosion product deposit layer under dynamic porosity evolution.

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