CN110428919B - Method for designing reactivity control strategy of pressurized water reactor nuclear power plant based on symptoms - Google Patents
Method for designing reactivity control strategy of pressurized water reactor nuclear power plant based on symptoms Download PDFInfo
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Abstract
The invention relates to a sign-based pressurized water reactor nuclear power plant reactivity control strategy design method, which comprises the following steps: (1) Classifying accident conditions according to the loss degree of the reactor core subcritical degree based on a neutron flux instrument reflecting the reactor core subcritical degree; (2) Respectively determining accident lists to be responded by reactor core reactivity control; (3) Performing reactive control strategy analysis to ensure that the control strategy can meet the processing requirement of the most severe accident condition; (4) verifying and confirming the reactivity control strategy; and (5) forming a final reactivity control strategy. The method is widely applied to pressurized water reactor nuclear power plants of different reactor types, has universal applicability and envelopment on handling accidents with abnormal reactivity, and can ensure the safety and effectiveness of reactivity control of the nuclear power plants.
Description
Technical Field
The invention belongs to the technical field of nuclear power plant design, and particularly relates to a sign-based design method of reactivity control strategies of a pressurized water reactor nuclear power plant.
Background
The deep defense is a safety design requirement throughout the design safety rules (HAF) implementation of nuclear power plants. The accident handling rule is used as a third defense line of the depth defense principle, and plays a vital role in limiting the accident development and ensuring the safety of the reactor. The symptom-oriented accident handling strategy integrates the advantages of an incident guiding accident rule and a state guiding accident rule, takes symptom-oriented accident handling as a main part, provides multi-level diagnosis multi-means countermeasures, and is mainly based on a key safety function, so that the accident can be relieved and handled quickly by adopting an optimal recovery rule through event guidance when the accident symptoms are obvious, and the safety of each barrier of a power plant can be ensured through the recovery guidance of the state tree guiding function of the key safety function when an unexplained accident or a superimposed accident occurs, so as to achieve the purpose of minimum radioactivity released into the environment. Reactivity control is one of three safety functions for ensuring the safety of a nuclear power plant, and the purpose of ensuring the subcritical reactor core in a controllable range is the primary objective of nuclear power plant control.
The nuclear power plant has high complexity, and for the pressurized water reactor nuclear power plant, besides a nuclear steam supply system and a thermodynamic system, a plurality of special safety facilities are arranged for ensuring safety. The number of systems in a nuclear power plant reaches hundreds, considering various auxiliary systems and support systems. Symptom-oriented accident guidance reactivity control relates to a large number of systems and equipment of a nuclear power plant, and all steps of strategies are mutually influenced and associated and need to be analyzed and determined based on a scientific and reasonable design method.
Disclosure of Invention
The invention aims to provide a sign-based design method for reactivity control strategies of a pressurized water reactor nuclear power plant, which classifies the reactivity control modes according to the subcritical loss degree, respectively determines the reactivity control strategies and verifies and confirms the correctness of the reactivity control strategies, thereby ensuring the safety and the effectiveness of the reactivity control of the nuclear power plant.
The technical scheme of the invention is as follows: a method for designing a reactivity control strategy of a pressurized water reactor nuclear power plant based on symptoms comprises the following steps:
(1) Classifying accident conditions according to the loss degree of the reactor core subcritical degree based on a neutron flux instrument reflecting the reactor core subcritical degree;
(2) Respectively determining accident lists to be dealt with by the reactor core reactivity control according to the classification in the step (1);
(3) Performing reactive control strategy analysis to ensure that the control strategy can meet the processing requirement of the most severe accident condition;
(4) Verifying and confirming the reactivity control strategy;
(5) Forming the final reactivity control strategy.
Further, the method for designing the reactivity control strategy of the pressurized water reactor nuclear power plant based on the signs as described above, wherein in the step (1), the accident conditions are classified based on the signs according to the degree of subcritical loss, and the method comprises the following steps:
1) The possibility of nuclear power production or nuclear power production;
2) The reactor core shutdown margin is insufficient.
Further, according to the method for designing the symptom-based reactivity control strategy for the pressurized water reactor nuclear power plant, in the step (2), typical accident conditions for the reactivity of the reactor core are determined according to accident safety analysis, probability analysis and simulation calculation, wherein the typical accident conditions corresponding to "1) the possibility of nuclear power generation or nuclear power generation" include:
a) An expected transient without a scram;
b) Other over-induction conditions of positive reactivity.
Further, according to the sign-based design method of the reactivity control strategy of the pressurized water reactor nuclear power plant, in the step (3), strategy analysis is carried out on the most unfavorable working condition of the reactivity control to determine a strategy framework, and meanwhile, the corresponding setting value of the relevant measures is determined through calculation and analysis; in order for the control strategy to meet the requirements of all accident conditions under the symptom, the mitigation strategy needs to be analyzed for the inclusion of the typical conditions of excessive introduction of positive reactivity, and if the typical conditions cannot be matched or included, the accident handling strategy needs to be adjusted to match all the typical conditions.
Further, in the method for designing the reactivity control strategy of the pressurized water reactor nuclear power plant based on the symptoms, in the step (4), the correctness of the strategy needs to be verified by performing written examination on the reactivity control strategy; meanwhile, the control effect of the reactivity and other parameters is confirmed by simulating the initial working condition of the typical accident and processing according to the accident processing strategy so as to confirm whether the reactivity control strategy meets the design requirement or not, and if the reactivity control strategy does not meet the requirement, the reactivity control strategy is determined again.
The invention has the following beneficial effects: the method for designing the reactivity control strategy of the pressurized water reactor nuclear power plant based on the symptoms is widely applicable to pressurized water reactor nuclear power plants of different reactor types. The method classifies the symptoms based on the severity of subcritical loss, on one hand, an operator can determine the severity of the current subcritical loss so as to determine the sequence of accident handling, on the other hand, analysis of handling strategies corresponding to working conditions can be performed according to different subcritical loss working conditions, and design of reactivity control strategies is performed respectively. The method is based on the fact that the accident condition with the worst reactivity is subjected to strategy and fixed value analysis, and the inclusion and matching of the strategy to other typical conditions are analyzed, so that the method has wide implementable significance for the design of the reactivity control strategy. The design method ensures the safety and effectiveness of the reactivity control strategy of the pressurized water reactor nuclear power plant based on symptoms.
Drawings
FIG. 1 is a flow chart of the symptom-based reactive control strategy design of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and examples.
Symptom-oriented accident guidance reactivity control involves a large number of systems and equipment in a nuclear power plant, and when a nuclear power plant reactivity control strategy is designed, the following problems need to be solved in an important way:
determining information that effectively monitors reactivity and classifying the accident symptoms according to the extent of subcritical loss.
Degree of critical loss of radix Yu Ci, determining a control strategy that can be used to mitigate and control core reactivity, respectively, for accident sign analysis.
The system has wide applicability and envelopment to the reactivity control of the pressurized water reactor nuclear power plant based on the signs and can be used for dealing with the accidents with abnormal reactivity.
A verification method for the reactive control strategy needs to be established and whether the strategy meets the requirements is verified.
Aiming at the technical problems to be solved, the invention provides a symptom-based design method for reactivity control strategy of an advanced pressurized water reactor nuclear power plant, the flow of the method is shown as figure 1, and the specific method comprises the following steps:
(1) And classifying the accident conditions according to the loss degree of the reactor core subcritical degree based on a neutron flux instrument reflecting the reactor core subcritical degree.
After a reactor scram, the neutron flux is expected to decrease rapidly and then decrease at a fixed rate to normal shutdown levels. After a few minutes, core heat generation comes primarily from decay heat of fission products, not nuclear fission itself. A rated power of 5% (in the case of a power plant) is greater than the decay power that a dedicated safety facility can carry, with greater than 5% indicating that an operator needs immediate action to prevent core damage. Considering the impact on the subcritical loss of the core, the classification according to severity can be based on symptoms:
1) Neutron flux > 5%, the possibility of nucleated power generation or nucleated power generation;
2) Neutron flux is less than or equal to 5%, and reactor core shutdown margin is insufficient.
(2) Taking "nuclear power generation or the possibility of nuclear power generation" as an example, a list of accidents that the core reactivity control needs to cope with is determined.
Depending on the type II operating condition event that occurs, there are a number of Anticipated Transients Without Scram (ATWS) based on accident safety analysis, probability analysis, and related simulation calculations. All ATWS transients are characterized by a mismatch between the power generated in one loop and the power carried away through the two loops. This causes the primary loop to heat up and boost until doppler and moderator temperature effects cause core power to begin to drop.
There are also several situations that can lead to "nucleated power production or the possibility of nucleated power production," the first being a reactor scram that is not complete, perhaps because some control rods are not inserted or because some control rods are not inserted to the end, but not to the extent that they can be considered ATWS. The second is the boron dilution of the primary loop, which is caused by the water source injected into the primary loop not being borated correctly in advance, or by the injection of the primary loop with the wrong water source. The third is primary overcooling, which may be due to secondary side pressure relief, or excessive SG feedwater, a negative moderator temperature coefficient will introduce positive reactivity.
Thus, typical accident conditions for core reactivity may be determined. The method comprises the following steps:
a) An expected transient state failing to scram;
b) Other positive reactivity overruns.
(3) Reactivity control strategy analysis
In order to analyze the accident condition of the reactive abnormality sign, the most unfavorable condition is analyzed first, and it is ensured that the control strategy can meet the processing requirement of the most severe accident condition. And carrying out strategy analysis aiming at the most unfavorable working condition of the reactivity control to determine a strategy framework, and determining a corresponding setting value of the relevant measure execution through calculation and analysis. The setting values applied in the accident handling strategy depend on the target to be achieved by the strategy and the target to be achieved by each sub-step, determine the effective execution of the whole strategy and have important significance for maintaining the safe operation of the nuclear power plant. Meanwhile, in order to enable the control strategy to meet the requirements of all accident conditions under the symptom, the compatibility of the mitigation strategy on the typical conditions with excessive introduction of the positive reactivity needs to be analyzed, and if the compatibility cannot be achieved or the compatibility cannot be achieved, the accident handling strategy needs to be adjusted to be matched with all the typical conditions.
(4) Reactive control strategy verification and validation
After the reactive control strategy is completed, verification and validation work needs to be carried out. The correctness of the written review policy is verified. And confirming by using a confirming tool, simulating a typical accident initial working condition, processing according to an accident processing strategy, and confirming the control effect of the reactivity and other parameters so as to confirm whether the reactive control strategy meets the design requirement, if not, re-determining the reactive control strategy.
(5) Form the final reactivity control strategy
Based on the analysis and validation results described above, a symptom-based reactive control strategy is developed.
Examples
The detailed implementation of the symptom-based design method for the reactivity control strategy of the advanced pressurized water reactor nuclear power plant will be described by taking a certain pressurized water reactor nuclear power plant as an example.
(1) Based on the neutron flux instrument reflecting the reactor core subcritical degree, the degree of loss of the reactor core subcritical degree is classified as follows:
the probability of nucleated power production or nucleated power production: when the power of the power range is more than 5%, the fission power is generated, and when the multiplication time of the intermediate range is more than 0, the fission power generates a precursor.
Insufficient reactor core shutdown margin: the source range multiplication time is greater than 0.
(2) A list of incidents that the core reactivity control needs to cope with is determined.
Taking the accident condition of "nuclear power generation or possibility of nuclear power generation" as an example for explanation, the list of the accident or the condition is as follows:
1) An expected transient without a scram;
2) Excessive introduction of positive reactivity:
part of the control rods are not inserted;
dilution of the boron of the primary circuit;
excessive cooling of the primary circuit.
Among these, the anticipated transient state of failure to scram may cause a primary circuit overpressure or DNBR overrun, the most unfavorable condition among "nuclear power generation or the possibility of nuclear power generation" accident conditions.
(3) And analyzing the reactivity control strategy.
For the anticipated transient accident without emergency shutdown, the measures needed to be taken by analysis mainly comprise reactor shutdown driving, control rod gravity shutdown, steam turbine trip, auxiliary feedwater starting, soluble poison injection (such as reactor emergency boron injection starting and reactor boron and water system control), steam generator water level control, isolated dilution passage, primary loop temperature regulation and finally confirming that the reactor is in a subcritical state, and corresponding setting values are executed by the related measures through calculation. The expected transient mitigation strategy failing the scram was further analyzed for its inclusion in other typical conditions where positive reactivity was over-introduced.
For "partial control rod non-insertion," mitigation strategies taken by anticipatory transients that fail to scram, including reactor shutdown, control rod gravity shutdown, and soluble poison injection, isolation of dilution channels, and loop temperature regulation, may be effective in mitigating this accident. Analysis of the "primary boron dilution" and "primary overcooling" conditions can also be accommodated by an anticipated transient mitigation strategy that fails to scram.
(4) Policy validation and validation is performed.
1) The written examination verifies the correctness of the policy.
2) And verifying the correctness of the accident handling strategy under the typical accident condition.
After verification and confirmation, the strategy can meet the requirement of accident handling.
(5) Forming the final reactivity control strategy.
Based on the analysis and verification and validation results described above, a symptom-based reactive control strategy is completed.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.
Claims (4)
1. A method for designing a reactivity control strategy of a pressurized water reactor nuclear power plant based on symptoms comprises the following steps:
(1) Classifying accident conditions according to the loss degree of the reactor core subcritical degree on the basis of a neutron flux instrument reflecting the reactor core subcritical degree;
(2) Respectively determining accident lists to be dealt with by the reactor core reactivity control according to the classification in the step (1);
(3) Performing reactive control strategy analysis to ensure that the control strategy can meet the processing requirement of the most severe accident condition; performing strategy analysis to determine a strategy framework according to the most unfavorable working condition of reactivity control, and determining a corresponding setting value of a relevant measure to execute through calculation and analysis; in order to enable the control strategy to meet the requirements of all accident conditions under the symptom, the control strategy needs to analyze the inclusion of typical conditions of excessive introduction of positive reactivity, if the typical conditions cannot be matched or included, the accident handling strategy needs to be adjusted to match all the typical conditions;
(4) Verifying and confirming the reactivity control strategy;
(5) Resulting in a final reactivity control strategy.
2. The sign-based design method for a reactivity control strategy for a pressurized water reactor nuclear power plant according to claim 1, wherein: in the step (1), according to the degree of subcritical loss, classifying accident conditions based on signs, including:
1) The possibility of nucleated power production or nucleated power production;
2) The reactor core shutdown margin is insufficient.
3. The symptom based design method for reactivity control strategy for a pressurized water reactor nuclear power plant according to claim 2, wherein: in the step (2), typical accident conditions for the reactivity of the reactor core are determined according to accident safety analysis, probability analysis and simulation calculation, wherein the typical accident conditions corresponding to the '1) possibility of nuclear power generation or nuclear power generation' include:
a) An expected transient state failing to scram;
b) Other positive reactivity overruns.
4. The sign-based design method for a reactivity control strategy for a pressurized water reactor nuclear power plant according to claim 1, wherein: in the step (4), the correctness of the strategy needs to be verified by performing written examination on the reactivity control strategy; meanwhile, the control effect of the reactivity and other parameters is confirmed by simulating the initial working condition of the typical accident and processing according to the accident processing strategy so as to confirm whether the reactivity control strategy meets the design requirement or not, and if the reactivity control strategy does not meet the requirement, the reactivity control strategy is determined again.
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| CN113257448B (en) * | 2021-04-21 | 2024-04-19 | 广东核电合营有限公司 | Control method and equipment for reactor extrapolation critical of nuclear power plant |
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