A method for analyzing small flow rate and temperature deviation of pressurizer spray valves in nuclear power plants

Abstract

This invention provides a method for analyzing low-flow and temperature deviations in the spray valve of a pressurizer in a nuclear power plant, comprising the following steps: Step 1: Establishing a heat transfer model for the spray valve pipeline to calculate heat transfer under different flow rates and predict temperature change trends; Step 2: Calculating the flow resistance coefficient of the pipeline at different valve core rotation angles under low flow rates; Step 3: Performing thermal expansion analysis of the valve core-seat clearance and transmission splines caused by temperature to obtain the flow area and flow resistance coefficient at the corresponding temperature; Step 4: Establishing an analysis model for the factors affecting the flow rate and temperature deviation of the spray valve, and conducting fault factor diagnosis analysis. This invention establishes a calculation model and analysis method for heat transfer, valve core rotation, and transmission mechanism linkage under the coupled effects of temperature, flow resistance, and flow rate, and ultimately establishes a design method for controlling temperature deviation and a fault analysis method for causing temperature deviation.

Description

Technical Field

[0001] This invention relates to the field of spray technology for pressurizers in nuclear power plants, and in particular to a method for analyzing small flow rates and temperature deviations in spray valves of pressurizers in nuclear power plants. Background Technology

[0002] For pressurized water reactor nuclear power plants, pressurizer spray is used to regulate the pressure of the primary loop, playing an important role in the safe operation of the power plant.

[0003] like Figure 1 As shown, the spray lines are located at the top of the pressurizer and can be divided into main spray and auxiliary spray depending on the source of the spray water. The main spray consists of parallel branches connecting to the pressurizer from two cold sections. Each branch includes an automatic flow control valve (RCP001VP and 002VP), which can start, regulate, and terminate the spray flow as needed by the operation control system. The two branches merge into a larger main pipe, and the spray water is injected into the steam space of the pressurizer through nozzles located at the top of the pressurizer, driven by the pressure head at the outlet of the main pump.

[0004] The main spray valves RCP001VP and RCP002VP are equipped with lower stops. When they are in the closed position, the lower stops slightly open the valves, creating a flow channel for continuous low-flow spraying, with a flow rate of approximately 230 L / h. This low-flow continuous spraying serves two main purposes: first, it reduces thermal stress and thermal shock when the main spray valves open or when transient fluctuations cause coolant ripples in and out of the pipes; second, it helps maintain the uniformity of water chemistry and temperature within the pressurizer.

[0005] Each spray line has a temperature sensor to monitor whether the spray flow rate is sufficient. The non-QSR periodic test procedures for the M310 unit require that the temperature difference between the two spray lines not exceed 5°C under NS / SG mode hot shutdown conditions. For a certain nuclear power unit, although the temperature difference between the two spray lines is maintained within the operating procedure requirements during the startup phase by adjusting the small flow rate threshold, after a period of power operation, due to various factors, the temperature difference between the two spray lines increases and cannot be maintained within the limit. This prevents the spray valves from receiving sufficient spray flow, affecting the primary loop pressure control.

[0006] Flow control of valves typically involves collecting multiple raw data points from control valves installed on industrial equipment. These raw data points are preprocessed to obtain target data. Regression fitting is then performed on this target data to derive a functional relationship between the valve opening and flow rate. Finally, this functional relationship is validated to determine the target function, which is then used to analyze the flow characteristics of the control valve. However, this method only focuses on changes in flow rate itself, neglecting the influence of temperature and the transmission structure on flow characteristics. When flow rate and temperature are coupled, it cannot promptly capture the impact of temperature changes on flow rate. Adjustments based solely on the flow rate curve often lead to over-adjustment, causing flow oscillations and resulting in flow imbalance.

[0007] In addition, a method for analyzing the temperature field of valves has been proposed. This method analyzes the valve's application, working environment, connection method with pipelines, and material properties, improving the overall performance analysis capability of valves under various conditions and working conditions, and effectively improving the accuracy of analysis and evaluation of special valves.

[0008] However, during the analysis, the influence of temperature changes on material expansion was not considered, and the impact of thermal expansion on the valve flow area could not be fully taken into account. Therefore, when analyzing the influence of temperature on flow rate changes, there was still a problem of inaccurate calculation of flow rate changes. At the same time, since only the influence of temperature on the valve was considered in one direction and the feedback effect of flow rate was not taken into account, the overall analysis results still had a large deviation.

[0009] Therefore, it is necessary to propose a coupled model that can couple temperature deviation, flow area (valve core rotation angle), and flow rate change, which can meet the existing needs of valve flow and temperature regulation and fault diagnosis. Summary of the Invention

[0010] The purpose of this invention is to provide a method for analyzing the small flow rate and temperature deviation of the spray valve in a nuclear power plant pressurizer, thereby solving the problem of diagnosing fault factors that cause abnormal temperature deviations during operation of the spray valve.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A method for analyzing small flow rate and temperature deviation of pressurizer spray valves in nuclear power plants includes the following steps:

[0013] Step 1: Establish a heat transfer model for the spray valve pipeline, realize heat transfer calculation of the pipeline under different flow rates, and predict the temperature change trend;

[0014] Step 2: Calculate the pipe system flow resistance coefficient for different valve core rotation angles under low flow conditions;

[0015] Step 3: Perform thermal expansion analysis of valve core-seat clearance and transmission spline caused by temperature to obtain the flow area and flow resistance coefficient at the corresponding temperature;

[0016] Step 4: Establish a model for analyzing the factors affecting the flow rate and temperature deviation of the spray valve, and conduct fault factor diagnosis and analysis.

[0017] In step 1, the heat conduction equation for the cylindrical straight tube is:

[0018]

[0019] In the formula, T is temperature, t is time, ρ is density, λ is thermal conductivity, C is heat capacity, and r is radial dimension. The circumferential dimension is z, the axial dimension is z, and the internal heat source power is Φ.

[0020] For the medium inside the circular tube, there is no internal heat source, and circumferential temperature deviation is ignored. Equation (1) can be further simplified to:

[0021]

[0022] Divide the pipeline system into a one-dimensional computational grid along the flow direction, discretize equation (2), and the heat transfer within each grid cell is as follows:

[0023]

[0024] Based on the change in heat, the temperature of the medium within the node at time step t+1 can be calculated:

[0025]

[0026] In the formula, A is the cross-sectional area of ​​the pipe, ΔL is the unit length, and Δt is the time step.

[0027] Because of the fluid flow, the coordinates of the fluid within the pipe at time t+1 need to be recalculated. Therefore, the temperature of the nth node at time t+1 is actually obtained from the fluid near node m at time t. The node number m can be calculated based on the time step and the fluid velocity.

[0028]

[0029] In the formula, V is the fluid velocity, and Int is the floor sign. Flooring takes into account that the distance the fluid travels within Δt is not an integer multiple of the unit length. The remaining length l after flooring is:

[0030] l=V·Δt-(nm)ΔL

[0031] Therefore, at time t+1, the fluid temperature at any node in the pipe can be obtained by linear interpolation of the upstream node m and the temperature at node m+1:

[0032]

[0033] In step 2, the flow resistance coefficient is obtained by calculating with computational fluid dynamics software:

[0034] R(θ) = ΔH / Q 2

[0035] Where, Q is the volume flow rate; ΔH is the pressure difference; R is the flow resistance coefficient.

[0036] Step 3 specifically includes:

[0037] Step 3.1: Calculate the change in the rotation angle caused by the thermal expansion clearance of the spline;

[0038] Step 3.2: Calculate the change in the flow-through area due to the thermal expansion of the valve core and the valve seat.

[0039] In step 3.1, the change in the spline rotation angle is:

[0040] Δθ1 = λ1θ1(T - T ref ) + θ ref1

[0041] Where, T is the temperature; θ1 is the rotation angle converted from the spacing referenced for the thermal expansion clearance of the spline fit; θ ref1 is the rotation angle of the valve core at the reference temperature T ref .

[0042] In step 3.2, the flow-through area is:

[0043]

[0044] Where, r is the inner diameter of the valve seat, and d is the clearance distance at the junction of the valve core and the valve seat.

[0045] [[ID=憨48]]Furthermore, when d << rd << r, the flow-through area is:

[0046]

[0047] According to the fact that the flow-through area at 290°C is 35% larger than that at 250°C, the inner diameter of the valve seat at any temperature is calculated to be

[0048] [[ID=憨58]]

[0049] Since 40λ r << 1, after rearrangement:

[0050]

[0051] Assuming that the change in r caused by thermal expansion is linear, the inner diameter of the valve seat is:

[0052] r + r It should be noted that there may be some inaccuracies in the translation due to the unclear or potentially incorrect original content in some parts (such as "憨48" and "憨58" which seem to be errors in the original). Please check and correct the original text for a more accurate translation.ref =λ r r ref (TT ref )

[0053] Then at any temperature:

[0054]

[0055] The gap at the junction of the valve core and valve seat is:

[0056]

[0057] The time interval change relative to 290℃ is as follows:

[0058]

[0059] The relative rate of change is:

[0060]

[0061] The calculated valve core rotation angle relative to the rotation angle at 290°C is as follows:

[0062]

[0063] Step 4 specifically includes:

[0064] Step 4.1: Determine the threshold value for the spline tooth mating clearance;

[0065] Step 4.2: Determine the crank mechanism connection clearance threshold;

[0066] Step 4.3: Determine the hinge connection gap threshold;

[0067] Step 4.4: Determine the pneumatic diaphragm gap threshold.

[0068] Furthermore, based on the valve core rotation angle deviation limit, the maximum value of the spline key tooth fit clearance ΔH1=R1θ can be obtained. Δ Based on the crank rotation radius R2, calculate the allowable limit of the connection clearance ΔH2 = R2θ Δ .

[0069] Furthermore, the deviation limit is calculated based on the crank angle α.

[0070] Compared with existing technologies, the method for analyzing small flow rates and temperature deviations of pressurizer spray valves in nuclear power plants provided by this invention has the following advantages:

[0071] This invention establishes a calculation model and analysis method for heat transfer, valve core rotation, and transmission mechanism linkage under the coupled effects of temperature, flow resistance, and flow rate. Finally, it establishes a design method for controlling temperature deviation and a fault analysis method for causing temperature deviation.

[0072] This invention, for the first time, comprehensively considers the coupled effects of temperature, flow resistance, and flow rate when the flow rate of a spray valve changes slightly, establishing an analytical model and calculation method for heat transfer in the piping system, thermal expansion of spray valve components, and changes in valve core angle. It not only studies the influence of flow rate on the temperature of the flowing medium in the piping system but also investigates the feedback effect of temperature on flow rate.

[0073] This invention analyzes the relationship between temperature deviation and valve core rotation angle when the flow rate of the spray valve changes at small intervals. It establishes for the first time a joint action model of temperature deviation, valve core rotation angle, and transmission mechanism under the influence of thermal expansion, and realizes the analysis of transmission mechanism design deviation and fault diagnosis.

[0074] This invention establishes an analytical model for the impact of clearance deviations of major components of the transmission mechanism on valve core rotation angle and spray valve temperature deviation, and obtains design deviations or fault thresholds for splines, crank structures, hinges, and pneumatic diaphragms. Attached Figure Description

[0075] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the technical description will be briefly introduced below.

[0076] Figure 1 A simplified diagram of the existing voltage regulator spray process;

[0077] Figure 2 A flowchart of the method for analyzing small flow rate and temperature deviation of the pressurizer spray valve in a nuclear power plant provided by the present invention;

[0078] Figure 3 A schematic diagram of the flow area at the junction of the valve core and valve seat provided by the present invention;

[0079] Figure 4 A schematic diagram of the vertical cross-section of the valve core-valve seat mating provided by the present invention;

[0080] Figure 5 A schematic diagram of the connecting components of the spray valve transmission structure provided by the present invention.

[0081] Figure 6 A schematic diagram of the spline structure connecting the valve core and the drive shaft provided by the present invention;

[0082] Figure 7 This is a schematic diagram of the crank and hinge connection mechanism provided by the present invention.

[0083] Explanation of reference numerals in the attached figures:

[0084] 1. Valve seat edge; 2. Valve core edge; 3. Valve core; 4. Valve seat; 5. Spray valve; 6. Spline; 7. First crank; 8. First hinge; 9. Pneumatic diaphragm; 10. Second crank; 11. Connecting rod; 12. Second hinge. Detailed Implementation

[0085] The following detailed description provides further details on specific implementation methods.

[0086] like Figure 2 As shown, this invention provides a method for analyzing small flow rate and temperature deviations in the pressurizer spray valve of a nuclear power plant, comprising the following steps:

[0087] Step 1: Establish a heat transfer analysis model for the relationship between the spray valve and the piping system, enabling real-time calculation and analysis of the impact of spray valve flow rate changes on pipe system heat dissipation and temperature. Step 2: Obtain the pipe system flow resistance coefficient for different valve core rotation angles under low flow rates through experiments and simulation calculations. Step 3: Conduct thermal expansion analysis of valve core-seat clearance and transmission spline caused by temperature, obtaining the variation law of flow area and the corresponding flow resistance coefficient at different temperatures. Step 4: Establish an analysis model for spray valve flow rate and temperature deviation factors, and conduct fault factor diagnosis analysis based on temperature difference.

[0088] This invention focuses on the coupled piping system of temperature, flow rate, and flow resistance coefficient. Through steps 1 to 3, it analyzes the temperature deviation between the spray valve and normal operating conditions, thereby diagnosing potential faults in the transmission mechanism and providing technical support for inspection and maintenance.

[0089] The present invention specifically includes the following:

[0090] Step 1: Establish a heat transfer model for the spray valve pipeline, realize heat transfer calculation of the pipeline under different flow rates, and predict the temperature change trend.

[0091] The piping between the cold section and the spray valve is typically tens of meters long. Although there is an insulation layer on the outside of the piping, when the spray valve is closed and only a small flow rate remains, the heat dissipation effect of the piping system is significant, showing a clear cooling trend. Thermal conductivity equation for cylindrical straight pipe:

[0092]

[0093] In the formula, T is temperature, t is time, ρ is density, λ is thermal conductivity, C is heat capacity, and r is radial dimension. The circumferential dimension is z, the axial dimension is z, and the internal heat source power is Φ.

[0094] Under insulation conditions, the temperature difference of the fluid at the same cross-section is small. We can ignore radial heat transfer within the fluid and only consider axial heat transfer, as well as heat dissipation through the insulation layer and the outside air. In this case, the above heat conduction equation for the cylindrical straight pipe simplifies to:

[0095]

[0096] Divide the piping system into a one-dimensional computational grid along the flow direction, discretize the above equation, and the heat transfer within each grid cell is as follows:

[0097]

[0098] In the formula, ΔQ represents the change in heat, expressed in W.

[0099] A is the cross-sectional area inside the pipe, ΔL is the element length, and Δt is the time step.

[0100] R1 is the thermal resistance of the air cavity between the insulation layer and the pipe wall per unit length, in mK / W;

[0101] R2 thermal resistance per unit length of insulation layer, unit: mK / W;

[0102] R3 is the convective thermal resistance per unit length, measured in mK / W.

[0103] After obtaining the heat dissipation, the fluid medium temperature in each cell at time step t+1 can be calculated from the fluid state and heat dissipation at the previous time step:

[0104]

[0105] Since fluid flows within each cell, a temperature mapping relationship between the fixed grid and the fluid needs to be established. Assuming that at time t, the fluid in the nth cell, after heat transfer calculation, flows downstream, and at time t+1, the fluid in that cell corresponds to the fluid in the upstream mth and m+1th cells, the location l within that grid is found based on the fluid flow calculation at the boundary between the mth and m+1th cells. The fluid temperature within this grid is calculated by interpolating the fluid temperatures of the mth and m+1th cells. Therefore, the fluid temperature at any location and time within the pipe system is calculated as follows:

[0106]

[0107] Step 2: Perform flow field calculations to obtain the pipe system flow resistance coefficient for different valve core rotation angles under low flow conditions of the spray valve.

[0108] The fluid flow rate in the piping system containing the spray valve is mainly related to the flow resistance of the spray valve at low flow rates. The flow resistance coefficient of the spray valve can be obtained experimentally or calculated using computational fluid dynamics (CFD) software. When using the CFD method, a model based on the actual spray valve needs to be created to generate the fluid computational domain. The CFD method can obtain the velocity and pressure fields of the fluid. Since the spray valve operates at low flow rates, even small changes in its rotation angle will affect the flow resistance. Therefore, it is necessary to perform simulation calculations for different valve core rotation angles to obtain its flow resistance coefficient.

[0109] R(θ) = ΔH / Q 2

[0110] In the formula, Q is the volumetric flow rate, with units of m³. 3 / h; ΔH is the pressure difference, in meters; R is the flow resistance coefficient, in meters per second (m). 3 / h) 2 .

[0111] Step 3: Analyze the thermal expansion of the valve core-seat clearance and transmission spline caused by temperature to obtain the flow area and flow resistance coefficient at the corresponding temperature. For example, the following formula is the flow resistance coefficient of a certain spray valve:

[0112]

[0113] In the formula, R represents the spray valve at a valve core rotation angle of θ. T The flow resistance coefficient at that time is expressed in m / (m). 3 / h) 2 .

[0114] Based on the flow resistance coefficient, the volumetric flow rate is:

[0115]

[0116] By obtaining the flow resistance coefficient and the pressure difference between the inlet and outlet, the flow rate of the fluid medium in the pipeline can be determined. Increased flow resistance reduces the flow rate of the medium in the pipeline system. Under heat dissipation conditions, the temperature of the medium in the pipeline also decreases, resulting in different thermal expansions, which in turn cause changes in the valve core angle and flow resistance. These three factors are coupled. The valve core angle θ in the presence of thermal expansion is expressed as:

[0117] θ = θ0 + Δθ

[0118] In the formula, θ0 is the set target rotation angle, which is related to the target spray flow rate; Δθ is the rotation angle deviation caused by various factors from the actuator through the transmission mechanism to the valve core.

[0119] Step 3.1: Angle change caused by thermal expansion gap of spline.

[0120] Assuming the thermal expansion of the spline is linearly related to temperature, with a coefficient of linear expansion of λ1, as temperature increases, thermal expansion causes the rotation angle to increase, tending towards opening the valve core; conversely, as temperature decreases, the rotation angle decreases, tending towards closing the valve core. Therefore, the change in rotation angle is:

[0121] Δθ1=λ1θ1(TT ref )+θ ref1

[0122] In the formula, T is the temperature in °C; θ1 is the angle converted from the reference spacing of the spline thermal expansion gap, which is related to the spline size; θ ref1 To be at the reference temperature T ref The rotation angle of the valve core.

[0123] For example, for a temperature change from 250 °C to 290 °C, so T ref = 250 °C. According to previous studies, the spacing at 290 °C is 18.02% larger than that at 250 °C. At this time, the above formula can be written as:

[0124] Δθ1 = (0.0045ΔT + 1)Δθ 250

[0125] Here, ΔT = T - 250, Δθ 250 is the angular deviation caused by the spline fit clearance at 250 °C and is related to the initial fit.

[0126] If 290 °C is used as the reference temperature, then it is:

[0127] Δθ1 = (1 - 0.0045ΔT)Δθ 290 where, ΔT = 290 - T, Δθ 290 is the angular deviation caused by the spline fit clearance at 290 °C.

[0128] Then for any temperature, the angle of rotation after the spline expands is:

[0129] θ T = θ 290 - 0.0045(290 - T)Δθ 290

[0130] Step 3.2: Change in the flow area due to the thermal expansion of the valve core and valve seat.

[0131] The flow area at the junction of the valve core and valve seat is affected by thermal expansion. As Figure 3 shown, it is mainly caused by the thermal expansion of the valve seat (r increases). The thermal expansion of the valve core is along the radius direction of the ball, and its expansion projection at this point can be ignored (that is, the edge of the valve core is approximately unchanged, that is, h remains unchanged). It can be seen that the flow area will increase under the action of thermal expansion. Figure 3 In, 1 is the edge of the valve seat, and 2 is the edge of the valve core.

[0132] Since the valve is in a nearly closed state and d is close to zero, the flow area can be approximated as:

[0133]

[0134] In the formula, r is the inner diameter of the valve seat, and d is the clearance distance at the junction of the valve core and valve seat. When d << r, the above formula can be simplified to:

[0135]

[0136] Assume that the change in r caused by thermal expansion is linear, and it is:

[0137] r+r ref =λ r r ref (TT ref )

[0138] Using 290℃ as a reference, and considering that the flow area at 290℃ increases by 35% compared to 250℃, we can conclude that:

[0139]

[0140] Due to 40λ r <<1, after simplification:

[0141]

[0142] Then at any temperature:

[0143]

[0144] The gap d at any temperature is:

[0145]

[0146] The time interval change relative to 290℃ is as follows:

[0147]

[0148] The relative rate of change is:

[0149]

[0150] like Figure 4 As shown, the change in clearance d can be equivalent to the change in valve core rotation angle:

[0151]

[0152] but:

[0153]

[0154] Figure 4 In the diagram, 3 represents the valve core, and 4 represents the valve seat.

[0155] Therefore, for any temperature, after the above thermal expansion, the valve core rotation angle relative to the rotation angle at 290℃ becomes:

[0156]

[0157] Thus, the valve core rotation angle θ at 290℃ is confirmed. 290 And the angular deviation Δθ caused by the thermal expansion gap of the spline 290 Then, the valve core rotation angle θ can be calculated based on the actual temperature.T Then, the flow resistance coefficient R(θ) is obtained based on the turning angle θ.

[0158] Step 4: Establish a model for analyzing the factors affecting the flow rate and temperature deviation of the spray valve, and conduct fault factor diagnosis and analysis.

[0159] Based on the above model, if the temperature deviation of the spray valve is to be controlled within a certain range, then according to the relationship between flow resistance coefficient, flow rate, and temperature, the opening or rotation angle deviation of the valve core also needs to be within a certain range, assumed to be θ. Δ Therefore, the entire transmission mechanism, especially at connecting components, must have corresponding limits for fit tolerances and deviations caused by wear. Fault diagnosis can be performed to support its design and the detection of wear and loosening during operation. For example... Figure 5 As shown, its transmission components mainly include four parts: spline, crank structure, hinge, and pneumatic diaphragm. Figure 5 In the diagram, 5 is the spray valve, 6 is the spline, 7 is the first crank, 8 is the first hinge, and 9 is the pneumatic diaphragm.

[0160] Step 4.1: Determining the threshold value of the spline tooth mating gap.

[0161] spline structure, such as Figure 6 As shown, based on the valve core rotation angle deviation limit, the maximum value of the spline key tooth fit clearance can be obtained as follows:

[0162] ΔH1=R1θ Δ

[0163] This can provide support for design or wear detection.

[0164] Step 4.2: Determining the threshold value of the crank mechanism connection gap.

[0165] Figure 7 In the diagram, 10 represents the second crank, 11 the connecting rod, and 12 the second hinge. The connection between the crank and the transmission rod involves both fit tolerances and wear. Based on the crank's rotation radius R2, the allowable limit for the connection clearance is calculated as follows:

[0166] ΔH2=R2θ Δ

[0167] Attention should be paid to tolerances in this area, and hard materials should be selected to prevent wear. This will provide support for the design and wear detection.

[0168] Step 4.3: Determining the hinge connection gap threshold.

[0169] This hinge structure also exhibits dimensional deviations due to fit tolerances and wear. Based on the crank angle α, the deviation limit is:

[0170]

[0171] It is evident that as the crank angle α decreases, ΔH3 also decreases. However, if the angle is too large, the torque under the same force is smaller, which is detrimental to power transmission. It is recommended to pay attention to the fit tolerances in this area, use hard materials to prevent wear, and ensure that the crank angle α is not too small when the valve core is closed. This will provide support for design and wear detection.

[0172] Step 4.4: Determination of the pneumatic diaphragm gap threshold.

[0173] The pneumatic actuator opens and closes the valve core by driving the valve stem with a pneumatic diaphragm and rotating the transmission shaft. Since the valve stem direction is the same as the direction of movement of the pneumatic diaphragm at this time, the deviation limit of the pneumatic diaphragm is the same as ΔH3.

[0174] The above provides deviation limits for each major connection to ensure that the valve core rotation angle deviation is within the allowable range. This ensures that the flow rate and temperature of the spray valve are within the specified range for the design or engineering application. If temperature deviations occur, these limits can be used for testing, providing data support for spray valve fault diagnosis and equipment upgrades.

[0175] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included 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 small flow and temperature bias analysis of a spray valve of a pressurizer of a nuclear power plant, characterized by, The method comprises the following steps: Step 1: a heat transfer model is established for the spray valve pipeline, heat transfer calculation of the pipeline under different flow rates is realized, and temperature variation trends are predicted; the heat conduction equation of a cylindrical straight pipe is as follows: In the formula, T is temperature, t is time, p is density, λ is thermal conductivity, C is heat capacity, r is the inner diameter of the valve seat, is the circumferential dimension, z is the axial dimension, and Φ is the inner heat source power. The heat transfer equation is obtained based on the heat conduction equation of the cylindrical straight pipe: The pipeline system is divided into one-dimensional calculation grids along the flow direction, the above heat transfer equation is discretized, and heat transfer in each grid unit is as follows: Obtaining the change in heat: In the formula, A is the cross-sectional area of the pipeline, ΔL is the unit length, Δt is the time step, R1 is the heat resistance of the air cavity between the heat preservation layer and the pipe wall per unit length, R2 is the heat resistance of the heat preservation layer per unit length, and R3 is the convective heat resistance per unit length; The fluid temperature at any position in the pipeline at any time is calculated as follows: Step 2: the flow resistance coefficient of the pipeline under different valve core rotation angles at a small flow rate of the spray valve is calculated; Step 3: the gap between the valve core and the valve seat caused by temperature and the heat expansion of the spline are analyzed, and the flow area and the flow resistance coefficient corresponding to the temperature are obtained; The method comprises the following steps: Step 3.1: the rotation angle change caused by the spline heat expansion gap is calculated; the spline rotation angle change is as follows: Δθ1 = λ1θ1(T-T ref )+θ ref1 In the formula, T is temperature; θ1 is a rotation angle converted from a pitch-matched thermal expansion gap reference interval; θ2 is a rotation angle of the valve core at the reference temperature T ref1 ref ; and θ is a rotation angle of the valve core at the temperature T.​ Step 3.2: the flow area change caused by the heat expansion of the valve core and the valve seat is calculated; the flow area is as follows: In the formula, r is the inner diameter of the valve seat, and d is the gap distance at the intersection of the valve core and the valve seat. When d << r, the flow area is as follows: The inner diameter of the valve seat is as follows: r = r ref + λ r r ref (T-T ref ) According to the 35% increase in the flow area at 290°C relative to the flow area at 250°C, the inner diameter of the valve seat at any temperature is calculated to be The gap distance at the interface between the valve core and the valve seat is The relative 290 °C time slot changes are: The relative change rate is: The valve core rotation angle with respect to the rotation angle at 290°C becomes Step 4: a spray valve flow and temperature deviation factor analysis model is established, and fault factor diagnosis analysis is performed.

2. The method of claim 1, wherein the method is a method of small flow and temperature bias analysis of a pressurizer spray valve of a nuclear power plant. In step 2, the flow resistance coefficient is calculated by using a fluid mechanics software: R(θ) = ΔH / Q 2 In the formula, Q is the volume flow rate, ΔH is the pressure difference, and R is the flow resistance coefficient.

3. The method of claim 1, wherein the method is a small flow and temperature bias analysis method for a pressurizer spray valve of a nuclear power plant. According to the valve core rotation angle deviation limit value, the maximum value of the spline key tooth fitting gap ΔH1=R1θ is obtained Δ ; According to the crank rotation radius R2, the limit value ΔH2=R2θ of the connection gap is calculated Δ ; According to the crank rotation angle α, the deviation limit value is calculated

Images