A method for formulating a load regulation operation plan for a pressurized water reactor unit

Abstract

The present invention discloses a method for formulating a load regulation operation plan for a pressurized water reactor unit, including steps of initializing the R control rod position, optimizing the total insertion time of the C control rods, and optimizing the boronization-dilution strategy. The present invention provides a standardized method for formulating a load regulation operation plan for a pressurized water reactor unit, which can meet the requirements of all scenarios requiring load regulation, that is, operators do not need individual experience and skills, and can complete the formulation of the operation plan according to this method.

Description

Technical Field

[0001] The present invention belongs to the technical support field of nuclear power plant operation, and relates to a calculation analysis method and process for the core of a pressurized water moderated and cooled reactor (pressurized water reactor), and particularly relates to a method for formulating a load (power) adjustment operation plan for a pressurized water reactor unit. Background Art

[0002] Currently, the in-service pressurized water reactor units at home and abroad are mainly second-generation pressurized water reactor nuclear power units. The core design of the second-generation units mainly considers the base load operation state at full power, and its ability to track and adjust the load according to the power grid demand is very limited. Therefore, when the unit needs to adjust the load level as planned, the operation personnel will submit the load adjustment plan to the technical support department in advance, and the technical support department will formulate a targeted operation plan through theoretical analysis. The technical support personnel generally determine the scheme iteration path based on the current operation characteristics of the core and past similar experiences. The whole process lacks necessary process standardization and quantitative evaluation in multiple dimensions such as the safety and economy of the scheme, and overly relies on the professional knowledge reserve and experience accumulation of relevant personnel.

[0003] The mainstream pressurized water reactor nuclear power units usually form the reactor core by arranging square fuel assemblies, Figure 1 which is its radial view. At the top of several fuel assembly positions in the reactor, there are control rod drive mechanisms, which adjust the control rod absorber to insert or withdraw axially into the core. The control rods are generally divided into main regulating rod groups, power compensation rod groups and shutdown rod groups according to their functions. Usually, the main regulating rod group is called the R rod, and the power compensation rod group is called the C rod, Figure 1 and also gives the typical distribution of different types of control rods in the reactor. The cores of different units will vary in the distribution of fuel and control rods, but the above characteristics are basically the same.

[0004] The reactor controls the reactor power by adjusting the reactivity. The reactivity adjustment means include two ways: chemical compensation by adjusting the soluble boron concentration in the coolant and mechanical compensation by adjusting the insertion position (rod position) of the control rods. In addition to adjusting the reactivity to make the core power output always meet the operation requirements, it is also necessary to control the shape of the core power distribution (especially the axial power distribution can always meet the requirements of the operation technical specification to ensure the safe operation of the reactor.

[0005] The chemical compensation method has the advantage of causing little disturbance to the core power distribution. However, its introduction for reactivity regulation is not as timely as that of mechanical compensation. At the same time, frequent boration and dilution of the coolant not only increase the operation complexity but also inevitably lead to an increase in the total amount of radioactive wastewater, affecting the economic level of core operation. Therefore, the chemical compensation method is usually used for reactivity control of slow-changing processes such as core burnup, xenon poisoning change, and relatively slow load changes. For relatively faster load change processes, mechanical compensation is usually also needed for reactivity control. The mechanical compensation method has the advantages of timely reactivity introduction and no additional generation of radioactive wastewater. However, while adjusting reactivity, it will also significantly change the core power distribution. While meeting the reactivity regulation requirements, it is also necessary to ensure that the core power distribution always meets the operation safety requirements, which poses high requirements for operation control. At the same time, during the load change process, the xenon poisoning distribution in the core will also deviate from the stable equilibrium xenon state, and the changes in xenon poisoning distribution and total amount will also have a significant impact on the core reactivity and power distribution, which further increases the complexity and uncertainty of operation control. For operators, the operation control during the load regulation process has always been one of the main difficulties in core operation.

[0006] For different mechanical compensation adjustment methods, the shutdown rods must always be outside the core during the load regulation process and cannot participate in reactivity regulation; only the main regulating rods and power compensation rods can be used for reactivity regulation. The allowable rod position range of the main regulating rods is strictly restricted. During the power operation stage, the time when the power compensation rods are allowed to be inserted into the core is also strictly restricted. It can be seen that the mechanical compensation adjustment method is still restricted by many conditions during specific implementation, which further increases the difficulty of operation control.

[0007] After the load regulation plan is determined, the operator will notify the plan to the technical support personnel, who will use the core calculation program to conduct theoretical calculation and simulation for this process. During specific simulation, the technical personnel need to, on the premise of meeting all the application restrictions related to reactivity regulation methods, adjust the soluble boron concentration, the positions of the main regulating rods, and the positions of the power compensation rods at each time point, so that the results of the theoretical simulation can meet the actual unit operation control requirements in terms of reactivity and axial power distribution control. Specifically for axial power distribution control, the constant axial offset (AO) is mostly used as the operation control target, that is, during the load change process, it is necessary to maintain the core AO value always near the preset standard value AO0. The calculation formula of AO is as follows:

[0008]

[0009] In the formula, P t and P bThey are the total powers of the upper and lower halves of the core along the axis respectively. In actual applications, AO is not directly referred to, but an index DI directly related to AO is referred to. The calculation formula of DI is:

[0010] DI = P × AO

[0011] P is the relative power level of the core (this value is 100% at full power). DI is also called the axial power deviation, which is mainly affected by the relative power level, xenon poison distribution and control rod positions. Among these, only the control rod positions can be used as a means to adjust DI. When calculating the core program, the control rod positions are usually searched and determined first. After determining the control rod positions that can meet the core DI control target, chemical compensation is used as the final adjustment means to meet the reactivity control requirements.

[0012] Since the above three adjustment methods will all affect the reactivity, and the changes in the positions of control rods with different functions will also affect DI. Obviously, there will not be a unique standard answer for the final operation plan, and the generation of the final plan will also be an iterative and asymptotic process. The formulation of the operation plan in the traditional load adjustment process lacks the standardization of the process. Technical support personnel often can only refer to past similar load adjustment processes to formulate the initial plan, and gradually adjust and iterate according to the calculation results of the initial plan until it fully meets the requirements. The relatively arbitrary iterative process is difficult to ensure the efficiency of the plan formulation process, and it is also difficult to control the safety and economic levels of the operation plan from a global perspective. Summary of the Invention

[0013] In summary, in the prior art, the formulation of the load adjustment operation plan lacks the necessary process standardization, and the actual feasibility of the operation plan is not fully considered, and there are many uncertain factors. The purpose of the present invention is to standardize the plan formulation process based on the existing core theoretical calculation tools, and provide a method for formulating the load adjustment operation plan of a pressurized water reactor unit, so that the formulated operation plan has good operability and can take into account the requirements of operation safety and economy.

[0014] The general idea of the method of the present invention is: during the load change process, still taking the constant AO as the control target, first search and determine the target positions of the main adjustment rods, and then further search and determine the positions of the power compensation rods; then fine-tune the positions of the main adjustment rods and power compensation rods according to the change curve of the critical boron concentration to optimize the boronization and dilution strategy, and then obtain the operation plan for the final load adjustment process.

[0015] For the convenience of elaborating the specific model of the method of the present invention, the following symbolic definitions are given for each key technical parameter:

[0016] · P: Unit power level;

[0017] · t: Operating time;

[0018] · i: The serial number of the discrete state point used for numerical simulation of the load change process, with the starting value being 0;

[0019] · R: The rod position of the main regulating rod;

[0020] ● C: The rod position of the power compensation rod;

[0021] ● PPM: The critical boron concentration;

[0022] · DI: The axial power deviation of the reactor core;

[0023] · AO0: The AO value corresponding to the normal AO operation strategy, and this value is a known condition;

[0024] Based on the aforementioned inventive concept, to achieve the object of the present invention, the following technical solution is adopted:

[0025] A method for formulating a load regulation operation plan for a pressurized water reactor unit, comprising the following steps:

[0026] 1) Initialization of the R rod position

[0027] First, use the reactor core calculation program to conduct a theoretical simulation of the load change process. Place the C rod outside the reactor core at all state points i, and search for the R rod position with AO0 as the target; at this stage, no limit interval for the R rod position is set. After the calculation is completed, the R rod position is recorded as R0(i);

[0028] After the search for the R rod position is completed, the calculation results at each state point are divided into three cases: ① The search target AO0 is successful, and the rod position meets the requirements of the operation limit interval; ② The search target AO0 is successful, but the rod position exceeds the operation limit interval; ③ The search target AO0 is unsuccessful;

[0029] For the first case, the searched R rod position can be directly accepted, and the R rod reset is completed;

[0030] For the second and third cases, the R rod needs to be reset. On the premise of not exceeding the limit range of the operation regulations, reset the R rod between its operation target rod position and the searched rod position R0(i); repeat until the search target AO0 is successful, and the R rod reset is completed;

[0031] After the R rod reset is completed, re - simulate the load regulation process, initialize the C rod position through the C rod position search target DI operation band function, and perform the operation band reset according to the calculation results. Relax the operation band at the non - compliant state points so that finally all state points DI can enter the reset DI operation band, and complete the R / C rod position initialization; record the initialized R / C rod positions as R1(i) and C1(i), and the critical boron concentration at this time is PPM1(i);

[0032] 2) Optimization of the total insertion time of the C control rod

[0033] Check whether the total insertion time of the C control rod in step 1) can meet the limit requirements of the operating procedures. If the limit requirements for the total insertion time of the C control rod are met, step 3) can be directly entered; if not, reselect the state point with a smaller inserted rod position in the C1(i) control rod position sequence, start the R / C control rod replacement search, first lift the C control rod completely out of the reactor to make DI positive, and make DI negative by inserting the R control rod to keep DI unchanged, so as to effectively shorten the total insertion time of the C control rod; record the R / C control rod positions as R2(i) and C2(i) respectively at this time, and the critical boron concentration as PPM2(i);

[0034] 3) Optimization of the boron addition-dilution strategy

[0035] Reset the critical boron concentration PPM2(i) in step 2), reduce the change range of the critical boron concentration, and reduce the frequency of small reciprocating operations of boron addition / dilution. Then, perform a critical rod position search again for the state point with the reset critical boron concentration. If both the R / C control rods can be used for the critical search, preferentially select the control rod with a greater reactivity microscopic value for the critical rod position search according to the reactivity microscopic value of their rod positions; considering that the change of the rod position will also affect DI, the operating band can be reset again before the critical rod position search to ensure that the DI calculation result can still meet the axial power distribution control requirements after the rod position adjustment; record the R / C control rod positions as R3(i) and C3(i) respectively at this time, and the reset boron concentration as PPM3(i), which is the final solution generated by the method of the present invention.

[0036] It should be noted that in the above steps, the search switch for the critical boron concentration is always kept open, that is, after determining the R / C control rod positions, the core will be finally maintained critical through the critical boron concentration search. Therefore, with each change of the rod position, the corresponding critical boron concentration PPM will also be updated.

[0037] The present invention provides a method for formulating a load regulation operation plan for a pressurized water reactor unit in a standardized manner, which can meet the requirements of all scenarios requiring load regulation, that is, operators do not need individual experience and skills, and can complete the formulation of the operation plan according to this method. Description of the Drawings

[0038] Figure 1 is a radial view of the core distribution.

[0039] Figure 2 is a flow chart of the present invention. Detailed Embodiment

[0040] Refer to the drawings. This embodiment includes the following steps:

[0041] 1) Initialization of the R control rod position

[0042] First, use the core calculation program to theoretically simulate the load change process. At all state points i, the C rods are placed outside the reactor, and the rod positions of the R rods are searched with AO0 as the target. In this stage, no limit interval for the rod positions of the R rods is set. After the calculation is completed, the rod positions of the R rods are recorded as R0(i).

[0043] After the search for the rod positions of the R rods is completed, the calculation results at each state point are divided into three cases: ① The search target AO0 is successful, and the rod positions meet the requirements of the operation limit interval; ② The search target AO0 is successful, but the rod positions exceed the operation limit interval; ③ The search target AO0 is not successful.

[0044] For the first case, the rod positions of the R rods obtained by the search can be directly accepted, and then the reset of the R rods is completed.

[0045] For the second and third cases, the reset of the R rods is required. On the premise that the limits of the operating procedures are not exceeded, the R rods are reset between their operating target rod positions and the searched rod positions R0(i); repeat until the search target AO0 is successful and the reset of the R rods is completed.

[0046] After the reset of the R rods is completed, re-simulate the load regulation process. Initialize the rod positions of the C rods through the search target DI operation band function of the C rod positions, and perform the reset of the operation band according to the calculation results. Relax the operation band at the state points that do not meet the requirements, so that finally all state points DI can enter the reset DI operation band, and complete the initialization of the R / C rod positions. Record the initialized R / C rod positions as R1(i) and C1(i), and the critical boron concentration at this time is PPM1(i).

[0047] 2) Optimization of the total insertion time of the C rods

[0048] Check whether the total insertion time of the C rods in step 1) can meet the limit requirements of the operating procedures. If the limit requirements for the total insertion time of the C rods are already met, directly proceed to step 3). If not, re-select the state points with smaller inserted rod positions in the C1(i) rod position sequence, start the search for replacing the R / C rods. First, lift the C rods completely out of the reactor to make DI positive, and then insert the R rods to make DI negative to keep DI unchanged, so as to effectively shorten the total insertion time of the C rods. Record the R / C rod positions at this time as R2(i) and C2(i), and the critical boron concentration as PPM2(i).

[0049] 3) Optimization of the boronization-dilution strategy

[0050] Reset the critical boron concentration PPM2(i) in step 2), reduce the change range of the critical boron concentration, and decrease the frequency of small reciprocating operations of boronization / dilution. Then, perform a critical rod position search again for the state point after the critical boron concentration is reset. If both the R / C rods can be used for the critical search, preferentially select the control rod with a greater reactivity microscopic value according to the reactivity microscopic value of its rod position for the critical rod position search. Considering that the rod position change will also affect the DI, the operating band can be reset again before the critical rod position search to ensure that the DI calculation result can still meet the axial power distribution control requirements after the rod position adjustment. Denote the R / C rod positions at this time as R3(i) and C3(i) respectively, and the reset boron concentration as PPM3(i), which is the final solution generated by the method of the present invention.

Claims

1. A method for formulating a load regulation operation plan for a pressurized water reactor unit, characterized in that Including the following steps: 1) Initialization of the R control rod position Firstly, use the core calculation program to conduct a theoretical simulation of the load change process. Place the C control rods outside the core at all state points i, and search for the R control rod position with AO0 as the target. At this stage, no limit interval for the R control rod position is set. After the calculation is completed, the R control rod position is recorded as R0(i); After the search for the R control rod position is completed, the calculation results at each state point are divided into three cases: ① The search target AO0 is successful, and the rod position meets the requirements of the operation limit interval; ② The search target AO0 is successful, but the rod position exceeds the operation limit interval; ③ The search target AO0 is unsuccessful; For the first case, the R control rod position obtained by the search can be directly accepted, and the R control rod reset is completed; For the second and third cases, the R control rod needs to be reset. On the premise of not exceeding the limit range of the operation regulations, reset the R control rod between its operation target rod position and the searched rod position R0(i); repeat until the search target AO0 is successful and the R control rod reset is completed; After the R control rod reset is completed, re-simulate the load regulation process, initialize the C control rod position through the C control rod position search target DI operation band function, and perform the operation band reset according to the calculation results. Relax the operation band at the non-conforming state points so that finally all state points DI can enter the reset DI operation band, and complete the R / C control rod position initialization; record the initialized R / C control rod positions as R1(i) and C1(i), and the critical boron concentration at this time is PPM1(i); 2) Optimization of the total insertion time of the C control rod Check whether the total insertion time of the C control rod in step 1) can meet the limit requirements of the operation regulations. If the limit requirement of the total insertion time of the C control rod is already met, it is possible to directly enter step 3); if not, re-select the state point with a smaller inserted rod position in the C1(i) rod position sequence, start the R / C control rod replacement search. First, lift the C control rod completely outside the core to make DI positive, and make DI negative by inserting the R control rod to keep DI unchanged, so as to effectively shorten the total insertion time of the C control rod; record the R / C control rod positions at this time as R2(i) and C2(i), and the critical boron concentration is PPM2(i); 3) Optimization of the boron addition-dilution strategy Reset the critical boron concentration PPM2(i) in step 2), suppress the change range of the critical boron concentration, reduce the frequency of small reciprocating operations of boron addition / dilution, and then conduct a critical rod position search again for the state points with the critical boron concentration reset. If both the R / C control rods can be used for the critical search, preferentially select the control rod with a greater reactivity microscopic value for the critical rod position search according to the reactivity microscopic value of its rod position; considering that the rod position change will also affect DI, the operation band reset can be performed again before the critical rod position search to ensure that the DI calculation result can still meet the axial power distribution control requirements after the rod position adjustment; record the R / C control rod positions at this time as R3(i) and C3(i), and the reset boron concentration is PPM3(i).

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