Displacement design method for overpressure protection valve of reactor coolant system

Abstract

The invention belongs to the technical field of pressurized water reactor coolant systems, and particularly relates to a displacement design method for an overpressure protection valve of a reactor coolant system. Comprising the following steps: step 1, initial calculation input; 2, establishing a conservation relational expression; step 3, a discrete solving process; 4, physical property updating; and 5, valve displacement is determined. The method has the beneficial effects that aiming at the problem that the design capacity is too proper due to the fact that the calculation input in the preliminary estimation process of the discharge capacity of the pressure relief valve of the pressure stabilizer excessively depends on experience and the calculation hypothesis is unreasonable, the reasonable thermal process hypothesis is introduced; a system pressure dynamic response analysis mathematical model caused by thermal expansion of a coolant system under a reactor coolant system-voltage stabilizer accident transient condition is established, so that the reasonable range of the discharge capacity of the pressure relief valve can be accurately determined, and the design demonstration period and precision of the discharge capacity of the pressure relief valve of the voltage stabilizer are remarkably shortened and improved; the method has the remarkable characteristics of clear principle and quick calculation.

Description

Technical Field

[0001] The invention belongs to the technical field of pressurized water reactor coolant systems, and in particular relates to a displacement design method for an overpressure protection valve of a reactor coolant system. Background Art

[0002] The overpressure protection function of the reactor coolant system (RCS) of a pressurized water reactor nuclear power plant is mainly composed of a pressurizer, a release valve / safety valve (hereinafter collectively referred to as a pressure relief valve), a spray valve, and a surge pipe connecting the pressurizer and the main coolant system. The pressure relief valve is usually set on the top of the pressurizer. Under some accident conditions, the heat sink of the reactor secondary loop system is lost, and the residual heat of the core cannot be effectively discharged, causing the coolant in the RCS to continue to expand due to heat, thereby causing the RCS pressure to continue to rise. If the system pressure exceeds the design pressure of the RCS, it will threaten the integrity of the primary loop pressure boundary, thereby causing radioactive substances to be released into the environment. In order to avoid this situation, a pressure relief valve is set on the top of the pressurizer. When the valve opening pressure is reached, the valve opens and discharges part of the fluid to reduce the pressure in the loop, thereby avoiding the continuous rise of RCS pressure and the occurrence of overpressure accidents. In HAF 102-2016 "Nuclear Power Plant Design Safety Regulations", it is clearly stated that "measures must be taken to ensure that the action of the pressure relief device can avoid overpressure at the pressure boundary of the reactor coolant system and will not cause radioactive materials to be directly released from the nuclear power plant to the environment." In the commercial nuclear power units under construction and already in operation in China, a pressure relief valve for overpressure protection is installed on the top of the pressurizer to prevent the reactor coolant system from overpressure due to thermal expansion of the coolant or increased loading under accident conditions. In terms of design, the displacement of the pressure relief valve should not be less than the overall maximum expansion rate of the RCS system coolant to ensure that the system pressure can be quickly reduced through the timely discharge of the valve. At the same time, an excessively large valve displacement design is bound to increase the difficulty of valve design and the cost of power plant construction. Therefore, the displacement design of the pressure relief valve should be as small as possible while meeting safety requirements. In current engineering design, the displacement design process of the pressure relief valve can be summarized into two steps: first, based on experience, the displacement of the pressure relief valve is preliminarily given, and then the overpressure analysis benchmark accident is selected to conduct a safety analysis of the system pressure response, and the overpressure analysis results are obtained and fed back to the system and equipment professionals. During this period, multiple rounds of design iterations are required to determine the total displacement and quantity of the safety valve. On this basis, the upstream and downstream pipelines and valve designs of the safety valve are optimized, and finally the overpressure protection design is completed. This type of design requires repeated iterative analysis of safety analysis and system design, which takes a long time, and it is difficult to confirm the total minimum displacement of the safety valve that meets the safety requirements. It is urgent to improve the design process and design methods. Summary of the invention

[0003] The purpose of the present invention is to provide a displacement design method for an overpressure protection valve of a reactor coolant system. In view of the problem that the calculation input in the preliminary estimation process of the displacement of a pressurizer relief valve relies too much on experience and the design capacity is excessive due to unreasonable calculation assumptions, a mathematical model for the dynamic response analysis of the system pressure caused by the thermal expansion of the coolant system under transient conditions of a reactor coolant system-pressurizer accident is established by introducing reasonable thermal process assumptions. This method can more accurately determine the reasonable range of the pressure relief valve displacement and significantly shorten the design demonstration period and accuracy of the pressurizer relief valve displacement.

[0004] The technical solution of the present invention is as follows: A method for designing the displacement of an overpressure protection valve of a reactor coolant system, comprising the following steps:

[0005] Step 1: Initial calculation input;

[0006] Step 2: Establish conservation relations;

[0007] Step 3: Discrete solution process;

[0008] Step 4: Update physical properties;

[0009] Step 5: Determine the valve displacement.

[0010] The input in step 1 includes:

[0011] The core residual heat power at time t after the reactor emergency shutdown, m RCS Reactor coolant system coolant mass, m SG Steam generator secondary side water charge, C RCS0 Initial RCS system average constant pressure specific heat capacity, C SG0 Initial SG secondary side average constant pressure specific heat capacity, P RCS0 Initial pressurizer steam space pressure, T RCS0 Initial RCS coolant average temperature, P SG0 Initial SG secondary side steam pressure.

[0012] In step 2, it is assumed that the average temperature change of the transient process coolant system is ΔT RCS and the average temperature change of the secondary side of the steam generator ΔT SG The same, we get:

[0013]

[0014] Then the energy conservation relationship of the core residual heat at time t after shutdown satisfies:

[0015]

[0016] Where: T RCS(t) is the average temperature of the coolant system at time t, T SG (t) is the average temperature of the secondary side of the steam generator at time t, C RCS is the temperature T RCS (t) Corresponding reactor coolant system, C SG T SG (t) Average specific heat capacity at constant pressure on the secondary side.

[0017] The step 3 includes the following:

[0018] Step 31: Assume that the thermodynamic process in the steam space of the pressurizer satisfies the description of adiabatic compression, and P RCS0 , T RCS0 , T RCS (t) P is calculated according to the following formula RCS (t):

[0019]

[0020] Among them, γ is the adiabatic coefficient of the gas. According to the thermodynamic properties of water, P RCS (t) and T RCS (t) Query the water properties table to calculate C RCS (t), C_rcs and C_SG are obtained based on the interpolated physical property table;

[0021] Due to ΔT RCS and ΔT SG are equal, so we have:

[0022] T RCS (t)-T RCS0 =T SG (t)-T SG0

[0023] From the above formula, we can get T SG (t), and then according to the thermodynamic properties of saturated steam, according to T SG (t) Look up the thermophysical properties table of saturated steam to obtain C SG (t);

[0024] Step 32: According to the energy conservation relationship:

[0025]

[0026] Calculate dT RCS (t) / dt, and then according to P RCS (t) and T RCS (t) Check the water properties table to determine (dv / dT RCS (t)) P ;

[0027] Step 33: Use the dT obtained in step 32 RCS (t) / dt and (dv / dT RCS (t)) p Thermophysical parameters of water:

[0028] dv / dt=(dT RCS (t) / dt)·(dv / dT RCS (t)) P

[0029] Get the determined dv / dt; then according to the P obtained in step 31 RDS (t) Query the water meter to determine the corresponding saturated steam density ρ sat (t).

[0030] The step 4 includes the step of obtaining dT according to step 32. RCS (t) / dt, according to:

[0031] T RCS (t+Δt)=(dT RCS (t) / dt)·Δt+T RCS (t)

[0032] Calculate T RCS (t+Δt), where Δt is the discrete time step;

[0033] The obtained T RCS (t+Δt) Return to step 31 of the discrete solution process in step 3.

[0034] The step 5 comprises:

[0035] Step 51: First determine P RCS (t) Whether the pressure relief valve opening pressure setting value P* is reached. If reached, the discharge volume at the time when the pressure relief valve opening pressure setting value is reached is not less than the volume change rate of the system coolant at that time as the basis for calculating the minimum discharge volume of the pressure relief valve, through dv / dt = (dv / dt) · (dv / dT) P* Calculate the dv / dt value at this time;

[0036] Step 52: According to Calculate the pressure relief valve displacement

[0037] The beneficial effects of the present invention are as follows: the present invention aims at the problem of excessive reliance on experience for calculation input in the preliminary estimation process of the pressure relief valve displacement of the pressurizer and excessive design capacity caused by unreasonable calculation assumptions. By introducing reasonable thermal process assumptions, a mathematical model for dynamic response analysis of system pressure caused by thermal expansion of the coolant system under transient conditions of reactor coolant system-pressurizer accident is established. The mathematical model can more accurately determine the reasonable range of the pressure relief valve displacement, significantly shorten the design demonstration period and accuracy of the pressure relief valve displacement of the pressurizer, has the remarkable characteristics of clear principle and fast calculation, and is suitable for guiding the design of the pressure relief valve displacement of the pressurized water reactor pressurizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention provides a flow chart of a method for designing the displacement of an overpressure protection valve in a reactor coolant system. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] The present invention provides a method for designing the displacement of an overpressure protection valve for a reactor coolant system. In order to solve the problem of excessive reliance on experience in the calculation input of the initial estimation process of the pressure relief valve displacement of a pressurizer, and the problem of excessive design capacity caused by unreasonable calculation assumptions, a reasonable thermal process description is introduced to simulate the physical process of the dynamic response of the system pressure caused by the thermal expansion of the coolant system under transient conditions of a reactor coolant system-pressurizer accident, and the pressure relief valve displacement is not less than the peak volume expansion rate of the RCS system as the basis for displacement estimation. This method can more accurately determine the reasonable range of the pressure relief valve displacement, significantly shorten the design demonstration cycle and accuracy of the pressure relief valve displacement of the pressurizer, and is suitable for guiding the design of the pressure relief valve displacement of a pressurizer reactor. The invention overcomes the problem of excessive valve displacement value design caused by relying solely on engineering experience, and has the significant characteristics of reasonable assumptions, clear mathematical principles, simple input, and fast calculation.

[0041] The present invention establishes a physical model of the process of thermal expansion of the reactor coolant caused by the generation of residual heat in the core based on the principle of energy conservation, introduces an adiabatic compression thermodynamic process hypothesis into the steam space at the top of the pressurizer to solve the system pressure at different times of the process of thermal expansion of the coolant, and obtains the rate of change of the water vapor specific volume of the pressurizer steam space with temperature by querying the water physical property table according to the coolant system pressure and the average temperature of the coolant, and then obtains the rate of change of the water vapor specific volume with time. Finally, the valve displacement is determined according to the design requirement of the pressurizer pressure relief valve displacement that "the discharge volume at the time when the pressure relief valve opening pressure constant is reached should not be less than the volume change rate of the system coolant at that time".

[0042] A method for designing the displacement of an overpressure protection valve of a reactor coolant system comprises the following steps:

[0043] Step 1: Initial calculation input

[0044] According to the preliminary design of the reactor coolant system, the core physical design, system equipment design, thermal hydraulic design and other disciplines provide the following relevant calculation parameters, including:

[0045] The core residual heat power at time t after the reactor emergency shutdown, W; m RCS : Reactor coolant system (RCS) coolant mass, kg; m SG : Water charge on the secondary side of steam generator (SG), kg; C RCS0 : initial RCS system average constant pressure specific heat capacity, J / kg / ℃; C SG0 : initial SG secondary side average constant pressure specific heat capacity, J / kg / ℃; P RCS0 : Initial pressurizer steam space pressure, Pa; T RCS0 : initial RCS coolant average temperature, °C; P SG0 : Initial SG secondary side steam pressure, MPa.

[0046] Enter the above parameters into a spreadsheet (such as Microsoft Excel, etc.) to facilitate further calculations.

[0047] Step 2: Establish conservation relations

[0048] Assume that the average temperature change of the transient process coolant system is ΔT RCS and the average temperature change of the secondary side of the steam generator ΔT SG The same, then:

[0049]

[0050] Then the energy conservation relation (differential form) of the core residual heat at time t after shutdown satisfies:

[0051]

[0052] in:

[0053] T RCS (t) is the average temperature of the coolant system at time t, °C; T SG (t) is the average temperature of the secondary side of the steam generator at time t, °C; RCS is the temperature T RCS (t) Corresponding reactor coolant system, J / kg / ℃; C SG T SG (t) Average specific heat capacity at constant pressure on the secondary side, J / kg / °C.

[0054] Step 3: Discrete solution process

[0055] These include:

[0056] Step 31: Assume that the thermodynamic process in the steam space of the pressurizer satisfies the description of adiabatic compression, and P RCS0 , T RCS0 , T RCS (t) P can be calculated according to the following formula RCS (t):

[0057]

[0058] Among them, γ is the adiabatic coefficient of the gas. According to the thermodynamic properties of water, P RCS (t) and T RCS (t) Query the water properties table to calculate C RCS (t). C_rcs and C_SG are obtained based on the interpolated physical property table.

[0059] Due to ΔT RCS and ΔT SG are equal, so we have:

[0060] T RCS (t)-T RCS0 =T SG (t)-T SG0

[0061] Therefore, T can be obtained from the above formula SG (t). According to the thermodynamic properties of saturated steam, T SG (t) Look up the thermophysical properties table of saturated steam to obtain C SG (t).

[0062] Step 32: According to the energy conservation relationship:

[0063]

[0064] Calculate dT RCS (t) / dt, and then according to P RCS (t) and T RCS (t) Check the water properties table to determine (dv / dT RCS (t)) P .

[0065] Step 33: Use the dT obtained in step 32 RCS (t) / dt and (dv / dT RCS (t)) p Thermophysical parameters of water:

[0066] dv / dt=(dT RCS (t) / dt)·(dv / dT RCS (t))P

[0067] Get the determined dv / dt; then according to the P obtained in step 31 RCS (t) Query the water meter to determine the corresponding saturated steam density ρ sat (t).

[0068] Step 4: Update physical properties

[0069] According to dT obtained in step 32 RCS (t) / dt, according to:

[0070] T RCS (t+Δt)=(dT RCS (t) / dt)·Δt+T RCS (t)

[0071] Calculate T RCS (t+Δt), where Δt is the discrete time step, which is determined by the user.

[0072] The obtained T RCS (t+Δt) Return to step 31 of the discrete solution process in step 3;

[0073] Step 5: Determine the valve displacement

[0074] Step 51: First determine P RCS (t) Whether the pressure relief valve opening pressure set value P* is reached. If it is reached (assuming that the time is t*), the discharge volume at the time when the pressure relief valve opening pressure set value is reached should not be less than the volume change rate of the system coolant at that time as the basis for calculating the minimum discharge volume of the pressure relief valve, through dv / dt = (dv / dt) · (dv / dT) P* The dv / dt value at this time is calculated.

[0075] Step 52: According to Calculate the pressure relief valve displacement

Claims

1. A method for designing the displacement of an overpressure protection valve of a reactor coolant system, characterized in that: The steps include: Step 1: Initial calculation input; Step 2: Establish conservation relations; Step 3: Discrete solution process; Step 4: Update physical properties; Step 5: Determine the valve displacement.

2. The method for designing the displacement of an overpressure protection valve of a reactor coolant system according to claim 1, characterized in that: The input in step 1 includes: The core residual heat power at time t after the reactor emergency shutdown, m RCS Reactor coolant system coolant mass, m SG Steam generator secondary side water charge, C RCS0 Initial RCS system average constant pressure specific heat capacity, C SG0 Initial SG secondary side average constant pressure specific heat capacity, P RCS0 Initial pressurizer steam space pressure, T RCS0 Initial RCS coolant average temperature, P SG0 Initial SG secondary side steam pressure.

3. The method for designing the displacement of an overpressure protection valve of a reactor coolant system according to claim 1, characterized in that: In step 2, it is assumed that the average temperature change of the transient process coolant system is ΔT RCS and the average temperature change of the secondary side of the steam generator ΔT SG The same, we get: Then the energy conservation relationship of the core residual heat at time t after shutdown satisfies: Where: T RCS (t) is the average temperature of the coolant system at time t, T SG (t) is the average temperature of the secondary side of the steam generator at time t, C RCS is the temperature T RCS (t) Corresponding reactor coolant system, C SG T SG (t) Average specific heat capacity at constant pressure on the secondary side.

4. A method for designing the displacement of an overpressure protection valve of a reactor coolant system according to claim 1, characterized in that: The step 3 includes the following: Step 31: Assume that the thermodynamic process in the steam space of the pressurizer satisfies the description of adiabatic compression, and P RCS0 , T RCS0 , T RCS (t) P is calculated according to the following formula RCS (t): Among them, γ is the adiabatic coefficient of the gas. According to the thermodynamic properties of water, P RCS (t) and T RCS (t) Query the water properties table to calculate C RCS (t), C_rcs and C_SG are obtained based on the interpolated physical property table; Due to ΔT RCS and ΔT SG are equal, so we have: T RCS (t)-T RCS0 =T SG (t)-T SG0 Through the above formula, we can get T SG (t), and then according to the thermodynamic properties of saturated steam, according to T SG (t) Look up the thermophysical properties table of saturated steam to obtain C SG (t); Step 32: According to the energy conservation relationship: Calculate dT RCS (t) / dt, and then according to P RCS (t) and P RCS (t) Check the water properties table to determine (dv / dT RCS (t)) P ; Step 33: Use the dT obtained in step 32 RCS (t) / dt and (dv / dT RCS (t)) p Relationship between thermophysical parameters of water: dv / dt=(dT RCS (t) / dt)·(dv / dT RCS (t)) P Get the determined dv / dt; then according to the P obtained in step 31 RCS (t) Query the water meter to determine the corresponding saturated steam density ρ sat (t).

5. The method for designing the displacement of an overpressure protection valve of a reactor coolant system according to claim 1, characterized in that: The step 4 includes the step of obtaining dT according to step 32. RCS (t) / dt, according to: T RCS (t+Δt)=(dT RCS (t) / dt)·Δt+T RCS (t) Calculate T RCS (t+Δt), where Δt is the discrete time step; The obtained T RCS (t+Δt) Return to step 31 of the discrete solution process in step 3.

6. A method for designing the displacement of an overpressure protection valve of a reactor coolant system according to claim 1, characterized in that: The step 5 comprises: Step 51: First determine P RCS (t) Whether the pressure relief valve opening pressure set value P* is reached. If reached, the discharge volume at the time when the pressure relief valve opening pressure set value is reached is not less than the volume change rate of the system coolant at that time as the basis for calculating the minimum discharge volume of the pressure relief valve, through dv / dt = (dv / dt) · (dv / dT) P* The dv / dt value at this time is calculated.

7. A method for designing the displacement of an overpressure protection valve of a reactor coolant system according to claim 6, characterized in that: The step 5 comprises: Step 52: According to Calculate the pressure relief valve displacement

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