Nitrogen stabilized pressure reactor thermal hydraulic numerical analysis method and equipment

Abstract

The invention discloses a thermal hydraulic numerical analysis method and equipment for a nitrogen pressure stabilization reactor, and relates to a combined analysis method of a one-dimensional system level thermal hydraulic analysis program and an equipment internal three-dimensional structure level CFD (computational fluid dynamics) program. Phenomena of nitrogen dissolution, migration, precipitation, accumulation and the like in the nitrogen pressure-stabilized reactor and thermal hydraulic effects caused by the phenomena are subjected to whole-process prediction, and the influence of the phenomena on loop flow heat transfer characteristics and key equipment working performance is further analyzed. According to the method, multi-dimensional and multi-scale computational analysis can be realized, on the basis of not consuming a large amount of computing power resources, the dissolution, migration, precipitation and accumulation behaviors of nitrogen in the coolant and the thermal hydraulic effect caused by the dissolution, migration, precipitation and accumulation behaviors are predicted, and check of a nitrogen pressure-stabilized reactor design scheme and formulation of an operation strategy are supported.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal-hydraulic analysis, and relates to a numerical analysis method and device for the thermal-hydraulics of a nitrogen pressurized reactor. Background Art

[0002] In the primary circuit of a nitrogen pressurized reactor, nitrogen is used as the working fluid in the gas space of the pressurizer. Although the solubility of nitrogen in the coolant is very low at normal temperature and pressure (~10 ppm), at the operating conditions of the reactor in steady state (~15 MPa, 300 °C), the solubility of nitrogen in water can reach 5000 ppm. Therefore, the nitrogen in the gas space of the pressurizer will continuously dissolve into the coolant through the gas-liquid interface until it is saturated. When the dissolved nitrogen concentration in the coolant is relatively high, once there is a large transient change in temperature and pressure or a reactor shutdown, the solubility of nitrogen will be greatly reduced, and the dissolved nitrogen in the coolant will become supersaturated and precipitate. After the precipitated bubbles form a two-phase flow, on the one hand, it will affect the resistance characteristics of the flow in the system, and on the other hand, the gas may accumulate in some areas of key equipment, affecting the working performance and life of the equipment. To accurately predict and analyze the above effects, it is necessary to carry out calculations on the behaviors of nitrogen dissolution, migration, precipitation, accumulation, etc. in the primary circuit.

[0003] However, most of the current thermal-hydraulic programs and related numerical analysis methods focus on steam pressurized reactors, and do not consider the above physical processes that nitrogen experiences in the primary circuit, such as dissolution, migration, precipitation, accumulation, etc., and the thermal-hydraulic effects they cause in nitrogen pressurized reactors. Summary of the Invention

[0004] Due to the above defects in the prior art, the present invention establishes a numerical analysis method for the thermal-hydraulics of a nitrogen pressurized reactor to predict the behaviors of nitrogen dissolution, migration, precipitation, accumulation, etc. in the coolant and the thermal-hydraulic effects they cause, support the verification of the design scheme of the nitrogen pressurized reactor and the formulation of the operation strategy, and ensure the safe operation of the nitrogen pressurized reactor.

[0005] To achieve the above object, in a first aspect, the present invention provides a numerical analysis method for the thermal-hydraulics of a nitrogen pressurized reactor, including the following steps:

[0006] S1. Determine the geometric structure and parameters of the reactor system loop, and establish a one-dimensional simplified model of the system loop; determine the geometric structure and parameters of the key equipment, and model its internal three-dimensional fluid domain according to the geometric structure; give the initial conditions and boundary conditions of the system, and formulate the system operation strategy;

[0007] S2. Divide the one-dimensional simplified model and the three-dimensional fluid domain into one-dimensional and three-dimensional calculation grids, and carry out grid sensitivity analysis to balance the calculation accuracy and the consumption of calculation resources, and obtain the grid division parameters;

[0008] S3. Take the given initial conditions, boundary conditions, and operation strategies as inputs, solve the one-dimensional thermal-hydraulic program on a one-dimensional computational grid to obtain the temperature, pressure, flow velocity, gas holdup, and dissolved nitrogen concentration distributions within the system loop; according to the positions of the key equipment in the system loop, transfer the local parameters obtained from the one-dimensional calculation as the initial and boundary conditions to the three-dimensional CFD (Computational Fluid Dynamic) program for solution; among them, based on the temperature and pressure at various locations in the system loop at the current time step, calculate the local nitrogen solubility in real time, and determine whether supersaturation will occur and precipitation will occur in combination with the local dissolved nitrogen concentration; if no precipitation occurs, advance to solve the equations for the next time step; if precipitation occurs, based on the interfacial mass transfer sub-model, calculate the precipitation mass source term caused by gas-liquid mass transfer, and solve for the growth of the diameter of the currently precipitated bubbles; according to the local flow field information, solve for the critical detachment size of the bubbles, compare it with the obtained bubble size, and determine whether the wall bubbles will detach; if detachment occurs, reset the wall bubble size to the initial gas nucleus size and start the next bubble growth cycle;

[0009] S4. Extract the solution results of the one-dimensional thermal-hydraulic program and the three-dimensional CFD program, evaluate the current system loop design scheme and operation strategies, and output the evaluation results.

[0010] The above technical solution realizes multi-dimensional and multi-scale computational analysis by considering the behaviors of nitrogen dissolution, migration, precipitation, and accumulation at the one-dimensional system level and the three-dimensional internal structure level of the equipment respectively, and uses the parameters obtained from the one-dimensional calculation as the input for the three-dimensional calculation, so as to realize the whole-process prediction of the behaviors of nitrogen dissolution, migration, precipitation, and accumulation of nitrogen in the coolant of the nitrogen pressure-stabilized reactor, and its effects on the flow and heat transfer characteristics of the primary loop and the working performance of key equipment, without consuming a large amount of computing resources.

[0011] Further, in the step S3, the one-dimensional thermal-hydraulic program solves to obtain the flow field, temperature field, and dissolved nitrogen concentration field information at the system loop level, and the three-dimensional CFD program solves to obtain the detailed flow field, temperature field, and dissolved nitrogen concentration field distribution information inside the key equipment.

[0012] Further, in the step S3, the solution method of the one-dimensional thermal-hydraulic program is similar to that of the three-dimensional CFD program, the difference lies in the dimensional difference, the time point when nitrogen precipitation occurs in the system loop obtained by the one-dimensional thermal-hydraulic program, and the amount of the precipitated gas are used as the input for the three-dimensional CFD program to improve the accuracy of the three-dimensional calculation results.

[0013] Further, the solution method of the one-dimensional thermal-hydraulic program includes the following steps:

[0014] S31. Set the boundary conditions and initialize the initial values at each node on the one-dimensional computational grid.

[0015] S32. Determine whether the current time step is greater than the end time of the solution; if so, the solution ends; if not, continue with the subsequent calculations.

[0016] S33. Discretely solve the mass, momentum, energy equations, and the component transport equation of dissolved nitrogen under the two-fluid model based on lumped parameters, where the source terms in each equation are calculated by selecting appropriate models.

[0017] S34. Based on the temperature and pressure at various locations in the system loop calculated in step S32 at the current time step, calculate the local nitrogen solubility in real time, and determine whether precipitation will occur after supersaturation by combining the local dissolved nitrogen concentration; the judgment criterion is that the local supersaturation is greater than the critical supersaturation :

[0018]

[0019] In the formula, is the local dissolved nitrogen concentration, is the local nitrogen solubility, is the surface tension coefficient at the corresponding temperature and pressure, is the bubble diameter, is the liquid-phase pressure (system pressure) at this moment; if precipitation does not occur, advance to solve the equations for the next time step; if precipitation occurs, based on the interfacial mass transfer sub-model, calculate the precipitation mass source term caused by gas-liquid interfacial mass transfer, and solve for the growth of the diameter of the currently precipitated bubbles; among them, the growth of the bubble diameter is approximately described by the free growth process of bubbles in an infinitely supersaturated fluid:

[0020]

[0021] In the formula, is the bubble radius, is the diffusion coefficient of the substance in the liquid phase, is the time, is the local nitrogen solubility, is the gas-phase density; the first term on the right side of the equation is the solution of the steady-state diffusion process, and the second term represents the transient change of the concentration boundary layer at the gas-liquid interface during the bubble growth process; the mass source term caused by gas-liquid interfacial mass transfer is obtained by corresponding to the growth of the bubble volume.

[0022] S35. Solve for the critical detachment size of the bubble based on the local flow field information, compare it with the bubble size obtained in step S34, and determine whether the wall bubble will detach. If detachment occurs, reset the wall bubble size to the initial gas nucleus size and start the next bubble growth cycle. Among them, for the case of low liquid phase velocity, the bubble detachment model considers the buoyancy force and the surface tension on the three-phase contact line to obtain the critical detachment diameter of the bubble:

[0023]

[0024]

[0025]

[0026] In the formula are the advancing contact angle and the receding contact angle of the gas-liquid-solid three-phase contact line respectively, is the diameter of the three-phase contact line, is the surface tension coefficient, is the liquid phase density, is the gas phase density, is the gravitational constant, is the bubble volume; for the case of high liquid phase velocity and strong shear near the wall, the critical detachment diameter of the bubble is calculated according to the following formula:

[0027]

[0028] Among them, is the dimensionless detachment bubble diameter, is the Péclet number, is the shear rate in the flow boundary layer, is the local supersaturation, is the gas constant, is the absolute temperature, is the Strouhal number, is the cavitation characteristic length, is the bubble detachment frequency, is the mainstream velocity; the detachment bubble size is positively correlated with the mainstream flow velocity and the shear rate near the wall;

[0029] S36. Recalculate the local dissolved nitrogen concentration and the gas holdup , and advance the solution of the equation for the next time step.

[0030] Further, in the step S33, the equations to be solved include the mass conservation equations of two phases, the energy conservation equation, the momentum conservation equation, the population balance equation, and the component transport equation of dissolved nitrogen; according to the operating condition range, the bubble size is grouped, and models including but not limited to two-phase flow models, turbulence models, wall functions, inter-phase force models, inter-phase mass transfer models, bubble wall precipitation and shedding models, and bubble coalescence and breakup sub-models are selected to calculate the source terms in each equation.

[0031] Further, in the step S33, the component transport equation of dissolved nitrogen considers the convection term, the diffusion term, and the source term, where the convection term is calculated using the local flow field information, and the diffusion term is obtained based on the local temperature gradient, the dissolved nitrogen concentration gradient, and the nitrogen diffusion coefficient.

[0032] Further, the two-phase flow model selects the Euler-Euler two-fluid model, and the bubble coalescence and breakup sub-model selects the Liao model.

[0033] Further, the range of the bubble size grouping is from 10 microns to 5 millimeters.

[0034] Further, in the step S34, the local nitrogen solubility is solved by a nitrogen solubility model established based on data fitting by interpolation of existing tables or a thermodynamic equilibrium method. The data fitting method is established based on an existing nitrogen solubility database. Its advantage is that only simple interpolation calculations are required, and the calculation speed is fast. The disadvantage is that the accuracy, accuracy, and applicable range are limited by the database. The advantage of the thermodynamic equilibrium method is that it is not limited by the database and has a wide applicable range, but it requires real-time calculation of thermodynamic equations and has a large amount of calculation.

[0035] On the other hand, the present invention provides a thermal-hydraulic numerical analysis device for a nitrogen pressure-stabilized reactor, including a memory storing executable program codes; a processor coupled to the memory; the processor calls the executable program codes stored in the memory for executing the thermal-hydraulic numerical analysis method for a nitrogen pressure-stabilized reactor as described above.

[0036] Compared with the prior art, the above invention has the following advantages or beneficial effects:

[0037] (1) The thermal-hydraulic numerical analysis method for a nitrogen pressure-stabilized reactor according to the present invention can realize the full-process prediction of behaviors such as the dissolution, migration, precipitation, and accumulation of nitrogen, and further analyze its influence on the loop flow and heat transfer characteristics and the working performance of key equipment.

[0038] (2) In the three-dimensional CFD solution program of the thermal-hydraulic numerical analysis method for the nitrogen pressure-stabilized reactor of the present invention, the effects of mass transfer and coalescence breakup on bubble size are considered, and the migration and aggregation behaviors of bubbles of different sizes are calculated more accurately by solving the population balance model, so as to more accurately evaluate the influence of two-phase flow on the working performance of key equipment.

[0039] (3) The thermal-hydraulic numerical analysis method for the nitrogen pressure-stabilized reactor of the present invention realizes multi-dimensional and multi-scale analysis and calculation through the one-dimensional thermal-hydraulic solution part and the three-dimensional CFD solution part, and well balances the calculation accuracy and computing power consumption. Description of the Drawings

[0040] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, the present invention and its features and advantages will become more obvious.

[0041] Figure 1 is the flow chart of the thermal-hydraulic numerical analysis method for the nitrogen pressure-stabilized reactor in the present invention;

[0042] Figure 2 is the flow chart of the solution part of the one-dimensional thermal-hydraulic program in the thermal-hydraulic numerical analysis method for the nitrogen pressure-stabilized reactor in the present invention. Specific Embodiments

[0043] The following further describes the structure of the present invention with reference to the drawings and specific embodiments, but it is not a limitation of the present invention.

[0044] In the following detailed description, many specific details are set forth to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that well-known algorithms and models are not shown in detail to avoid obscuring the gist of the present invention; and the technologies not detailed in the following effect embodiments are existing technologies that can be retrieved.

[0045] Embodiment

[0046] Please refer to Figure 1 , this embodiment provides a thermal-hydraulic numerical analysis method for a nitrogen pressure-stabilized reactor, including the following steps:

[0047] S1. Determine the geometric structure and parameters of the reactor system loop, and establish a one-dimensional simplified model of the system loop; determine the geometric structure and parameters of the key equipment, and model its internal three-dimensional fluid domain according to the geometric structure; given the initial conditions and boundary conditions of the system, formulate the system operation strategy. The key equipment here is the equipment that is actually concerned, such as the main pump, residual drain pump, primary side of the steam generator, primary side of the heat exchanger, core sub-channel, ion exchanger, etc. of the reactor system.

[0048] S2. Based on the one-dimensional simplified model of the system loop and the three-dimensional fluid domain inside the key equipment, divide the one-dimensional and three-dimensional computational grids, conduct grid sensitivity analysis, balance the computational accuracy and computational resource consumption, and obtain appropriate grid division parameters.

[0049] S3. Take the given initial conditions, boundary conditions, and operating strategies as inputs, solve the one-dimensional thermohydraulic program on the one-dimensional computational grid to obtain the temperature, pressure, flow velocity, gas holdup, and dissolved nitrogen concentration distributions within the system loop; according to the position of the key equipment in the system loop, transfer the local parameters obtained from the one-dimensional calculation as the initial and boundary conditions to the three-dimensional CFD program for solution; more specifically, the one-dimensional thermohydraulic program solves to obtain the flow field, temperature field, and dissolved nitrogen concentration field information at the system loop level, and the three-dimensional CFD program solves to obtain the detailed flow field, temperature field, and dissolved nitrogen concentration field distribution information inside the key equipment. Among them, based on the temperature and pressure at various locations in the system loop at the current time step, calculate the local nitrogen solubility in real time, and combine the local dissolved nitrogen concentration to judge whether supersaturation will occur and precipitation will take place; if no precipitation occurs, advance to solve the equations for the next time step; if precipitation occurs, based on the interfacial mass transfer sub-model, calculate the precipitation mass source term caused by gas-liquid interfacial mass transfer, and solve for the growth of the diameter of the currently precipitated bubbles; according to the local flow field information, solve for the critical detachment size of the bubbles, compare it with the solved bubble size, and judge whether the wall bubbles will detach; if detachment occurs, reset the wall bubble size to the initial gas nucleus size and start the next bubble growth cycle.

[0050] As an example, refer to Figure 2 , the solution method of the one-dimensional thermohydraulic program includes the following steps:

[0051] S31. Set the boundary conditions and initialize the initial values at each node on the one-dimensional computational grid.

[0052] S32. Judge whether the current time step is greater than the end time of the solution; if so, the solution ends; if not, continue with the subsequent calculations.

[0053] S33. Discretely solve the mass, momentum, energy equations, and the component transport equation of dissolved nitrogen under the lumped parameter two-fluid model, where the source terms in each equation are calculated by selecting appropriate models.

[0054] S34. Based on the temperature and pressure at various locations in the system loop calculated in step S32 at the current time step, calculate the local nitrogen solubility in real time, and combine the local dissolved nitrogen concentration to judge whether supersaturation will occur and precipitation will take place; the judgment criterion is that the local supersaturation is greater than the critical supersaturation :

[0055]

[0056] In the formula, is the local dissolved nitrogen concentration, is the local nitrogen solubility, is the surface tension coefficient at the corresponding temperature and pressure, is the bubble diameter, is the liquid-phase pressure (system pressure) at this moment; if precipitation does not occur, the equation solution for the next time step is advanced. Among them, the local nitrogen solubility can be solved based on the data fitting of the existing table interpolation or the nitrogen solubility model established by methods such as thermodynamic equilibrium. If precipitation occurs, based on the interfacial mass transfer sub-model, the precipitation mass source term caused by the gas-liquid interfacial mass transfer is calculated, and the diameter growth of the currently precipitated bubble is solved; among them, the diameter growth of the bubble can be approximately described by the free growth process of the bubble in an infinitely supersaturated fluid:

[0057]

[0058] In the formula, is the bubble radius, is the diffusion coefficient of the substance in the liquid phase, is the time, is the local nitrogen solubility, is the gas-phase density; the first term on the right side of the equation is the solution of the steady-state diffusion process, and the second term represents the transient change of the concentration boundary layer at the gas-liquid interface during the bubble growth process; the mass source term caused by the gas-liquid interfacial mass transfer is obtained by corresponding to the growth of the bubble volume.

[0059] S35. According to the local flow field information, solve the critical detachment size of the bubble, compare it with the bubble size obtained in step S34, and judge whether the wall bubble will detach. If detachment occurs, reset the wall bubble size to the initial gas nucleus size and start the next bubble growth cycle. Among them, for the case of low liquid-phase flow velocity, the bubble detachment model analyzes the forces and considers the buoyancy force acting on the bubble and the surface tension at the three-phase contact line to obtain the critical detachment diameter of the bubble:

[0060]

[0061]

[0062]

[0063] In the formula are the advancing contact angle and the receding contact angle of the gas-liquid-solid three-phase contact line respectively, is the diameter of the three-phase contact line, is the surface tension coefficient, is the liquid-phase density, is the gas-phase density, is the gravitational constant, is the bubble volume; for the case of higher liquid-phase flow velocity and stronger shear near the wall, the critical detachment diameter of the bubble is calculated according to the following formula:

[0064]

[0065] where, is the dimensionless detachment bubble diameter, is the Péclet number, is the shear rate in the flow boundary layer, is the local supersaturation, is the gas constant, is the absolute temperature, is the Strouhal number, is the cavitation characteristic length, is the bubble detachment frequency, is the mainstream velocity; the detachment bubble size is positively correlated with the mainstream flow velocity and the shear rate near the wall.

[0066] S36. Recalculate the local dissolved nitrogen concentration and the gas holdup , and advance to solve the equations for the next time step.

[0067] In this embodiment, the diameter growth of the precipitated bubbles is obtained by solving the R - P equation. The critical detachment size of the bubbles is related to the flow shear near the wall and is calculated using the shear rate. This solution is derived from the analysis of the actual physical process, has practical physical significance, and is highly operable.

[0068] The solution method of the three-dimensional CFD program is similar to that of the one-dimensional thermohydraulic program. The differences lie in the dimensionality, the time point when nitrogen precipitation occurs in the system loop obtained by solving the one-dimensional thermohydraulic program, and the amount of the precipitated gas, which are used as the inputs of the three-dimensional CFD program.

[0069] S4. Extract the solution results of the one-dimensional thermohydraulic program and the three-dimensional CFD program, evaluate the current system loop design scheme and operation strategy, and output the evaluation results.

[0070] In this embodiment, the component transport equation of dissolved nitrogen mainly considers the convection term, diffusion term, and source term. Among them, the convection term is calculated using local flow field information, and the diffusion term is obtained based on the local temperature gradient, dissolved nitrogen concentration gradient, and nitrogen diffusion coefficient. In this embodiment, the three-dimensional CFD program is solved using FLUENT or CFX software, and some sub-models are embedded by user-defined functions. The equations solved by the three-dimensional CFD program include the mass conservation equations of two phases, energy conservation equations, momentum conservation equations, population balance equations, and component transport equations of dissolved nitrogen. According to the operating condition range, appropriate bubble size groups are set, and suitable two-phase flow models, turbulence models, wall functions, interphase force models, interphase mass transfer models, bubble coalescence and breakup sub-models, etc. are selected. The bubble size falling off the wall surface into the mainstream in the reactor system loop is on the order of dozens of micrometers, and it is difficult for bubbles larger than 5 mm to exist stably for a long time under the reactor flow conditions. In this embodiment, the bubble size grouping range is from 10 micrometers to 5 mm to ensure that most of the precipitated bubble sizes in the reactor system are covered.

[0071] In this embodiment, the Euler-Euler two-fluid model is selected as the two-phase flow model, and the Liao model is selected as the bubble coalescence and breakup sub-model. Compared with the Euler-Lagrange model, the Euler-Euler model consumes less computing resources when the number of bubbles is large. Compared with the Mixture model, the Euler-Euler model solves the conservation equations of gas and liquid phases separately, with higher accuracy. The bubble coalescence and breakup mechanism considered in the Liao model is relatively comprehensive. According to the literature, its prediction accuracy of bubble size distribution is higher than that of other models in many scenarios.

[0072] Compared with the existing reactor thermal-hydraulic analysis methods, the present invention considers phenomena such as nitrogen dissolution, migration, precipitation, and accumulation and the resulting thermal-hydraulic effects from the one-dimensional simplified model at the system level to the three-dimensional fluid model at the equipment level, providing a more effective numerical analysis means for predicting the behavior of nitrogen dissolution, migration, precipitation, and accumulation in the coolant of a nitrogen pressure-stabilized reactor and analyzing its impact on the primary loop thermal-hydraulics.

[0073] The above-mentioned thermal-hydraulic numerical analysis method for a nitrogen pressure-stabilized reactor can be executed by a thermal-hydraulic numerical analysis device for a nitrogen pressure-stabilized reactor. The device includes a memory storing executable program codes; a processor coupled to the memory; the processor calls the executable program codes stored in the memory for executing the above-mentioned thermal-hydraulic numerical analysis method for a nitrogen pressure-stabilized reactor.

[0074] Optionally, the memory may include, but is not limited to, high-speed random access memory and non-volatile memory. For example, one or more disk storage devices, flash memory devices, or other non-volatile solid-state storage devices; the processor may include, but is not limited to, a central processing unit (CPU), a graphics processing unit (GPU), a network processor (NP), etc.; it may also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components.

[0075] In summary, the present invention provides a method and device for numerical analysis of the thermal-hydraulics of a nitrogen-stabilized reactor. Through a combined analysis method of a one-dimensional system-level thermal-hydraulics analysis program and a three-dimensional structure-level CFD program inside the device, the present invention predicts the whole process of phenomena such as nitrogen dissolution, migration, precipitation, and accumulation in the nitrogen-stabilized reactor and the resulting thermal-hydraulic effects, and further analyzes its impact on the flow and heat transfer characteristics of the loop and the working performance of key equipment. The present invention can achieve multi-dimensional and multi-scale computational analysis. Without consuming a large amount of computing power resources, it can be used to predict the behavior of nitrogen dissolution, migration, precipitation, and accumulation in the coolant and the resulting thermal-hydraulic effects, and support the verification of the design scheme and the formulation of the operation strategy of the nitrogen-stabilized reactor.

[0076] Those skilled in the art should understand that those skilled in the art can implement variations in combination with the prior art and the above embodiments, which will not be elaborated here. Such variations do not affect the essence of the present invention and will not be elaborated here.

[0077] The above describes the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments. The devices and structures not described in detail should be understood to be implemented in a common manner in the art; any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes, without departing from the scope of the technical solution of the present invention, which does not affect the essence of the present invention. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the protection of the technical solution of the present invention.

Claims

1. A thermal hydraulic numerical analysis method for a nitrogen pressurized reactor, characterized in that: The following steps are involved: S1. Determine the geometric structure and parameters of the reactor system loop and establish a one-dimensional simplified model of the system loop; determine the geometric structure and parameters of key equipment and obtain its internal three-dimensional fluid domain based on the geometric structure modeling; Given the initial conditions and boundary conditions of the system, formulate the system operation strategy; S2, dividing the one-dimensional simplified model and the three-dimensional fluid domain into one-dimensional and three-dimensional computational grids, and performing grid sensitivity analysis to balance computational accuracy and computational resource consumption, and obtaining grid division parameters; S3. Taking the given initial conditions, boundary conditions and operation strategies as input, solving the one-dimensional thermal hydraulic program on the one-dimensional computational grid, and obtaining the temperature, pressure, flow rate, gas content and dissolved nitrogen concentration distribution in the system loop; according to the position of the key equipment in the system loop, passing the local parameters obtained by the one-dimensional calculation as the initial boundary conditions to the three-dimensional CFD program and solving; wherein, based on the temperature and pressure at each location of the system loop at the current time step, the local nitrogen solubility is calculated in real time, and combined with the local dissolved nitrogen concentration, it is judged whether precipitation will occur after reaching supersaturation; if precipitation does not occur, the equations of the next time step are advanced for solution; if precipitation occurs, the precipitation mass source term caused by gas-liquid phase mass transfer is calculated based on the interphase proton transfer model, and the diameter growth of the current precipitation bubble is solved; according to the local flow field information, the critical bubble shedding size is solved, and compared with the solved bubble size, it is judged whether the wall bubble will fall off, and if it does fall off, the wall bubble size is reset to the initial gas core size, and the next bubble growth cycle begins; S4. Extract the solution results of the one-dimensional thermal hydraulic program and the three-dimensional CFD program, evaluate the current system loop design and operation strategy, and output the evaluation results.

2. A thermal hydraulic numerical analysis method for a nitrogen pressurized reactor according to claim 1, characterized in that: In step S3, the one-dimensional thermal hydraulic program solves the flow field, temperature field and dissolved nitrogen concentration field information at the system loop level, and the three-dimensional CFD program solves the detailed flow field, temperature field and dissolved nitrogen concentration field distribution information inside the key equipment.

3. A thermal hydraulic numerical analysis method for a nitrogen pressurized reactor according to claim 1 or 2, characterized in that: In step S3, the one-dimensional thermal-hydraulic program solution method is similar to the three-dimensional CFD program solution method, except that the dimensional difference, the time point when nitrogen precipitation occurs in the system loop obtained by solving the one-dimensional thermal-hydraulic program and the amount of precipitated gas are used as inputs of the three-dimensional CFD program.

4. A thermal hydraulic numerical analysis method for a nitrogen pressurized reactor according to claim 3, characterized in that: The one-dimensional thermal hydraulic program solving method comprises the following steps: S31, setting boundary conditions and initializing the initial values ​​of each node on the one-dimensional computational grid; S32, judging whether the current time step is greater than the solution end time; if so, the solution ends; if not, continuing with subsequent calculations; S33. Discretely solve the mass, momentum, energy equations and the component transport equation of dissolved nitrogen under the two-fluid model based on lumped parameters, where the source terms in each equation are calculated by selecting an appropriate model; S34, based on the temperature of each part of the system loop at the current time step calculated in step S32 ,pressure , calculate the local nitrogen solubility in real time, and combine the local dissolved nitrogen concentration to determine whether precipitation will occur after supersaturation; the judgment criterion is the local supersaturation Greater than critical supersaturation : ， In the formula, is the local dissolved nitrogen concentration, is the local nitrogen solubility, is the surface tension coefficient at the corresponding temperature and pressure, is the bubble diameter, is the liquid phase pressure (system pressure) at that moment; if precipitation does not occur, the equation of the next time step is advanced to solve; if precipitation occurs, the precipitation mass source term caused by gas-liquid phase mass transfer is calculated based on the interphase proton transfer model, and the diameter growth of the current precipitated bubble is solved; among them, the diameter growth of the bubble is approximately described by the free growth process of the bubble in an infinite supersaturated fluid: ， In the formula, is the bubble radius, is the diffusion coefficient of the substance in the liquid phase, For time, is the local nitrogen solubility, is the gas phase density; the first term on the right side of the equation is the solution of the steady-state diffusion process, and the second term represents the transient change of the gas-liquid interface concentration boundary layer during the bubble growth process; the mass source term caused by the gas-liquid phase mass transfer is obtained by the corresponding growth of the bubble volume; S35. According to the local flow field information, the critical bubble shedding size is solved, and compared with the bubble size solved in step S34 to determine whether the wall bubble will fall off. If it does fall off, the wall bubble size is reset to the initial gas core size and the next bubble growth cycle begins. For the case of low liquid phase flow rate, the bubble shedding model considers the buoyancy of the bubble through force analysis. Surface tension at the contact line of three phases The critical bubble detachment diameter is obtained as follows: ， ， ， In the formula are the advancing contact angle and receding contact angle of the gas-liquid-solid three-phase contact line, is the diameter of the three-phase contact line, is the surface tension coefficient, is the liquid density, is the gas phase density, is the gravitational constant, is the bubble volume; for the case of high liquid phase flow rate and strong shear near the wall, the critical shedding diameter of the bubble is calculated according to the following formula: ， in, is the dimensionless detached bubble diameter, is the Péclet number, is the shear rate in the boundary layer of the flow, is the local supersaturation, is the gas constant, is the absolute temperature, is the Strauhal number, is the characteristic length of the cavitation, is the bubble detachment frequency, is the mainstream velocity; the size of the detached bubble is positively correlated with the mainstream flow velocity and the shear rate near the wall; S36. Recalculate the local dissolved nitrogen concentration according to the previous steps and gas content , and move forward to solve the equations for the next time step.

5. A thermal hydraulic numerical analysis method for a nitrogen pressurized reactor according to claim 4, characterized in that: In the step S33, the equations to be solved include the mass conservation equation, energy conservation equation, momentum conservation equation, group balance equation, and component transport equation of dissolved nitrogen of the two phases; according to the operating range, bubble size grouping is set, and selections include but are not limited to two-phase flow model, turbulence model, wall function, phase force model, phase mass transfer model, bubble wall precipitation and shedding model, and bubble coalescence and fragmentation sub-model to calculate the source terms in each equation.

6. A thermal hydraulic numerical analysis method for a nitrogen pressurized reactor according to claim 5, characterized in that: In step S33, the component transport equation of dissolved nitrogen takes into account the convection term, diffusion term and source term, wherein the convection term is calculated using local flow field information, and the diffusion term is obtained based on the local temperature gradient, dissolved nitrogen concentration gradient and nitrogen diffusion coefficient.

7. The thermal hydraulic numerical analysis method of a nitrogen pressurized reactor according to claim 5, characterized in that: The two-phase flow model uses the Euler-Euler two-fluid model, and the bubble coalescence and breakup sub-model uses the Liao model.

8. The thermal hydraulic numerical analysis method for a nitrogen pressurized reactor according to claim 5, characterized in that: The bubble size groupings range from 10 microns to 5 mm.

9. The thermal hydraulic numerical analysis method for a nitrogen pressurized reactor according to claim 5, characterized in that: In step S34, the local nitrogen solubility is solved based on the data fitting of the existing table interpolation or the nitrogen solubility model established by the thermodynamic equilibrium method.

10. A thermal hydraulic numerical analysis device for a nitrogen pressurized reactor, characterized in that: It comprises a memory storing executable program code; a processor coupled to the memory; the processor calls the executable program code stored in the memory to execute the thermal-hydraulic numerical analysis method for a nitrogen-regulated pressure reactor according to any one of claims 1 to 9.

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