Critical operation control method for nuclear power unit reactor

Abstract

The invention relates to the field of nuclear power operation control, in particular to a nuclear power unit reactor critical reaching operation control method. The control method comprises the following steps: step 1, determining a reactivity change rate through calculation and observation; 2, determining a critical opportunity by using an extrapolation mapping method; and 3, combining the calculated value with observation, and determining the opportunity of stopping water injection. The control method can accurately grasp the opportunity of stopping water injection and ensure the safety of the reactor core.

Description

Technical Field

[0001] The invention relates to the field of nuclear power operation control, and in particular to a critical operation control method for a nuclear power unit reactor. Background Art

[0002] Nuclear power plants use the energy released by the controlled chain fission reaction in the reactor to produce electricity. Only in the critical state can the chain fission reaction output energy continuously and stably. Each time a nuclear power plant is restarted after shutdown, it needs to be operated to reach criticality, which is also an operation that requires high caution and precise control. Any slight deviation and abnormality may lead to reactivity deviation, which may lead to short-term events or accidental criticality of the reactor in serious cases.

[0003] Tianwan Nuclear Power Plant has a strict control plan for the critical operation of the reactor. The current operation method is to first replace water with a large flow rate to the startup interval, and then inject clean water at a small flow rate in the startup interval to achieve criticality. However, due to the small water injection flow rate, there is a lag time for clean water to enter the core, and there is also a lag time for the change in core reactivity, so it is necessary to stop the water injection in advance when the small flow rate of clean water injection reaches criticality. The decision to stop water injection is based on the core reactivity reaching a certain value. However, since the critical boron concentration value is not exactly the same each time the unit is started and reaches criticality, the reactivity change rate is different when a small flow of clean water is injected in a circuit. Too much or too little water injection affects the timing of reaching criticality, and may even cause boron injection or rod insertion due to excessive water injection, which may cause the control rod position to exceed the required range. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a nuclear power unit reactor critical operation control method, formulate a specific method for confirming the timing of stopping small flow water injection in the reactor, prevent the increase of operation volume due to inaccurate grasp of the timing of stopping water injection when reaching critical operation, and ensure the safety of the core.

[0005] The present invention provides a method for controlling critical operation of a nuclear power plant reactor, comprising the following steps:

[0006] Step 1: Determine the rate of change of reactivity by calculation and observation;

[0007] Step 2: Use extrapolation mapping to determine when the critical moment is reached;

[0008] Step 3: Combine calculated values ​​with observations to determine when to stop water injection.

[0009] In a specific embodiment of the present invention, in step 1, the method for calculating the reactivity change rate is:

[0010] Before water injection, the amount of clean water to be injected is calculated based on the current boric acid concentration in the first circuit and the critical boric acid concentration value; the water injection time is calculated based on the amount of clean water;

[0011] The reference reactivity change rate is calculated based on the injection time and the current primary circuit reactivity.

[0012] In a specific embodiment of the present invention, in the step 1,

[0013] Water injection is performed according to a reference rate of change of reactivity;

[0014] During the actual water injection process, the reactivity is measured using the external nuclear measurement system to observe the actual rate of reactivity change.

[0015] In a specific embodiment of the present invention, the step 2 specifically includes:

[0016] Draw an extended straight line through the reactivity change curve and intersect it with the line of 0 reactivity to obtain the expected critical point and critical time T 临 ; In the process of extrapolating the critical point, the reactivity curve of each reactivity measurement channel intersects with the straight line of their respective reactivity of 0 to find the critical point with the latest time.

[0017] In a specific embodiment of the present invention, in step three, the calculated value is compared with the observed value, and the value reached first is determined as the timing to stop water injection.

[0018] In a specific embodiment of the present invention, the method for calculating the timing of stopping water injection is:

[0019] Using the water injection delay time T 滞 and the expected critical boric acid concentration C 临 Calculate the reactivity of a circuit when water injection is stopped 停 .

[0020] In a specific embodiment of the present invention, the method for obtaining the observed value is:

[0021] Use the external nuclear test system to monitor the reactivity curve and determine the critical time point T 临 and water injection delay time T 滞 , using the critical time T 临 Subtract the water injection effect lag time T 滞 Get the appropriate time to stop water injection T 停 .

[0022] Compared with the prior art, the critical operation control method of a nuclear power plant reactor of the present invention has the following beneficial effects:

[0023] (1) Provide a control method for stopping water injection when a nuclear power plant reactor reaches critical operation, to ensure nuclear safety when the reactor reaches criticality under different initial operating conditions;

[0024] (2) Provide a control method for stopping water injection when a nuclear power plant reactor reaches critical operation, to ensure that the reactor reaches criticality safely and reliably at one time;

[0025] (3) Provide a control method for stopping water injection when a nuclear power plant reactor reaches critical operation, so as to ensure that the reactive effect introduced by the injection of clean water is just released under different initial operating conditions;

[0026] (4) There is no need to perform a large number of control rod insertion and boron injection operations to suppress reactivity. Even if there is a slight error, it can be stabilized by inserting or lifting the control rod 1 to 2 steps, reducing the amount of operations when reaching criticality and lowering the risk of human error.

[0027] (5) By calculating the reactivity value at the time of water outage in advance, continuously observing the reactivity change curve, calculating the time to stop water injection, and using the linear extrapolation method to find the precise time to stop water injection. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram showing the implementation of a critical operation control method for a nuclear power unit reactor. DETAILED DESCRIPTION

[0029] In order to further understand the present invention, the embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the present invention.

[0030] An embodiment of the present invention discloses a method for controlling critical operation of a nuclear power plant reactor, comprising the following steps:

[0031] Step 1: Determine the rate of change of reactivity by calculation and observation;

[0032] Since the critical boric acid concentration is not consistent each time, the core reactivity change rate is inconsistent when reaching criticality with the same water injection flow rate, which requires calculation and actual observation.

[0033] The method for calculating the reactivity change rate is:

[0034] Before water injection, the amount of clean water to be injected is calculated based on the current boric acid concentration in the first circuit and the critical boric acid concentration value; the water injection time is calculated based on the amount of clean water;

[0035] The reference reactivity change rate is calculated based on the injection time and the current primary circuit reactivity.

[0036] Water injection is performed according to a reference rate of change of reactivity;

[0037] During the actual water injection process, the reactivity is measured using the external nuclear measurement system to observe the actual rate of reactivity change.

[0038] Step 2: Use extrapolation mapping to determine when the critical moment is reached;

[0039] Specifically, it includes: drawing an extended straight line through the reactivity change curve and intersecting it with the straight line with reactivity of 0 to obtain the expected critical point and critical time T 临 ; In the process of extrapolating the critical point, the reactivity curve of each reactivity measurement channel intersects with the straight line of their respective reactivity of 0 to find the critical point with the latest time.

[0040] Step 3: Combine calculated values ​​with observations to determine when to stop water injection.

[0041] Specifically: compare the calculated value with the observed value, and determine the value reached first as the time to stop water injection.

[0042] The method for calculating the timing of stopping water injection is:

[0043] Using the water injection delay time T 滞 and the expected critical boric acid concentration C 临 Calculate the reactivity of a circuit when water injection is stopped 停 , this reactivity value can be used as a reference for water outage timing.

[0044] The water injection lag time is an empirical value. Since the lag time of introducing reactivity by injecting clean water is related to the water injection flow rate, the larger the water injection flow rate, the shorter the lag time. Although the critical boron concentration of the primary circuit changes each time when it reaches the critical point, the state of the primary circuit and the clean water injection flow rate are basically unchanged when reaching the critical point, so the reactive lag time of water injection is basically the same, which can be recorded and quoted as an empirical value. Of course, the value can also be verified and corrected at the beginning of each water change to obtain a more accurate value.

[0045] The method to obtain the observed value is:

[0046] Use the external nuclear test system to monitor the reactivity curve and determine the critical time point T 临 and water injection delay time T 滞 , using the critical time T 临 Subtract the water injection effect lag time T 滞 Get the appropriate time to stop water injection T 停 .

[0047] In order to further understand the present invention, the critical operation control method of a nuclear power plant reactor provided by the present invention is described in detail below in conjunction with embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0048] Example 1

[0049] Step 1: Determine the rate of change of reactivity

[0050] Since the critical boric acid concentration is not consistent each time, the core reactivity change rate is inconsistent when reaching criticality with the same water injection flow rate, which requires calculation and actual observation.

[0051] a) Calculation: Before water injection, calculate the amount of clean water to be injected based on the current primary circuit boron concentration value and the critical boric acid concentration value given in advance, and then calculate the reference water injection time based on the injection clean water flow rate. Calculate the reference reactivity change rate based on the calculated water injection time and the current primary circuit reactivity.

[0052] b) Observation: Since the calculated data always have errors when performing actual reactivity-related operations, the calculated reactivity change rate is used for reference. The accurate reactivity change rate must be obtained through actual observation. When the clean water is injected into the primary circuit to reach the critical value, the reactivity change is almost a straight line increase. Because of this premise, the extrapolation drawing method can be used to confirm.

[0053] Step 2: Extrapolate the critical timing

[0054] During the criticality process, the reactivity measurement of the ex-core nuclear measurement system is a continuous monitoring parameter that can be effectively utilized. Figure 1 As shown, the expected critical point and critical time Tc can be obtained by drawing an extended straight line through the reactivity change curve and intersecting it with the straight line with reactivity of 0. In the process of extrapolating the critical point, the reactivity curve of each reactivity measurement channel intersects with the straight line with reactivity of 0 to find the critical point with the latest time.

[0055] Step 3: Determine when to stop water injection

[0056] a) Calculation: Determine the water injection delay time T 滞 Then, according to the expected critical boric acid concentration C 临 Calculate the reactivity of a circuit when water injection is stopped 停 , this reactivity value can be used as a reference for water outage timing.

[0057] ln(C 停 / C 临 )×300=2.8×60×T 滞 ÷1000

[0058]

[0059] Where:

[0060] 300: Water loading capacity of one circuit (tons);

[0061] 2.8: Small flow rate of clean water injection speed (kg / s);

[0062] Boric acid differential value;

[0063] β eff : effective delayed neutron fraction;

[0064] b) Determined by actual observation

[0065] like Figure 1 As shown, the critical time point T is determined 临 and water injection delay time T 滞 After that, it only takes the critical time T 临 Subtract the water injection effect lag time T 滞 It is easy to get the appropriate time to stop water injection T 停 .

[0066] Calculated reactivity ρ 停 The water injection stop timing T determined by observation 停 Compare and determine which value is reached first, and then determine it is the time to stop water injection.

[0067] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0068] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling critical operation of a nuclear power plant reactor, characterized in that: The following steps are involved: Step 1: Determine the rate of change of reactivity by calculation and observation; Step 2: Use extrapolation mapping to determine when the critical moment is reached; Step 3: Combine calculated values ​​with observations to determine when to stop water injection.

2. The method for controlling the critical operation of a nuclear power plant reactor according to claim 1, characterized in that: In the step 1, the method for calculating the reactivity change rate is: Before water injection, the amount of clean water to be injected is calculated based on the current boric acid concentration in the first circuit and the critical boric acid concentration value; the water injection time is calculated based on the amount of clean water; The reference reactivity change rate is calculated based on the injection time and the current primary circuit reactivity.

3. The method for controlling the critical operation of a nuclear power plant reactor according to claim 2, characterized in that: In the step 1, Water injection is performed according to a reference rate of change of reactivity; During the actual water injection process, the reactivity is measured using the external nuclear measurement system to observe the actual rate of reactivity change.

4. The method for controlling critical operation of a nuclear power plant reactor according to claim 1, characterized in that: The step 2 specifically includes: Draw an extended straight line through the reactivity change curve and intersect it with the line of 0 reactivity to obtain the expected critical point and critical time T 临 ; In the process of extrapolating the critical point, the reactivity curve of each reactivity measurement channel intersects with the straight line of their respective reactivity of 0 to find the critical point with the latest time.

5. The method for controlling critical operation of a nuclear power plant reactor according to claim 1, characterized in that: In the step three, the calculated value is compared with the observed value, and the value reached first is determined as the timing to stop water injection.

6. The critical operation control method for a nuclear power plant reactor according to claim 5, characterized in that: The method for calculating the timing of stopping water injection is: Using the water injection delay time T 滞 and the expected critical boric acid concentration C 临 Calculate the reactivity of a circuit when water injection is stopped 停 .

7. The critical operation control method for a nuclear power plant reactor according to claim 5, characterized in that: The method to obtain the observed value is: Use the external nuclear test system to monitor the reactivity curve and determine the critical time point T 临 and water injection delay time T 滞 , using the critical time T 临 Subtract the water injection effect lag time T 滞 Get the appropriate time to stop water injection T 停 .

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