A method and a computing device for core damage assessment based on the dose rate outside the containment

Abstract

A method for evaluating core damage based on the dose rate outside the containment vessel, comprising the following steps: providing a core damage evaluation database including the degree of core damage and the dose rates at multiple detection points outside the containment vessel under typical accident sequences of a nuclear power plant; establishing a regression model based on a recurrent neural network, training with the core damage evaluation database, and establishing a mapping relationship between the dose rate at the detection point, the degree of core damage, and accident variables to form a core damage degree evaluation model; inputting the accident information to be evaluated and evaluating it with the core damage degree evaluation model. This method does not rely on the detection system inside the reactor containment vessel, improving the reliability and evaluation efficiency of the core damage degree evaluation under accident conditions. The present invention also provides a computing device.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear power, and particularly relates to a method and a computing device for evaluating core damage based on the dose rate outside the containment vessel. Background Art

[0002] When a core accident occurs in a nuclear power plant, it is necessary to promptly evaluate the degree of core damage as the basis for nuclear accident emergency response decisions and take corresponding measures to prevent the accident from deteriorating further. At present, domestic nuclear power plants mainly refer to the 3D / 3P method of France and the CDAG method of the United States, and use the core outlet temperature and the radiation dose rate inside the containment vessel as the key parameters for evaluating the severity of core damage. In some technical solutions, methods for detecting information inside the containment vessel such as the hydrogen concentration inside the containment vessel, the composition and temperature of the primary coolant, and the water level in the pressure vessel are also used to further improve the completeness of core damage assessment. However, the existing technical measures rely heavily on the detection system inside the containment vessel. During an accident, especially in the middle and late stages of the accident, the temperature, pressure, and highly radioactive environment inside the containment vessel will pose a great test to the effectiveness of the detection system. If the accuracy of the monitoring data of the detection system inside the containment vessel deviates, the assessment of the degree of core damage will be misled. Therefore, providing a method for evaluating core damage based on the dose rate outside the containment vessel has high value for improving the accuracy of nuclear accident assessment. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for evaluating core damage based on the dose rate outside the containment vessel, which evaluates the degree of core damage without relying on the detection data inside the containment vessel. The present invention also provides a computing device.

[0004] According to an embodiment of one aspect of the present invention, a method for evaluating core damage based on the dose rate outside the containment vessel is provided. The method includes the following steps:

[0005] a) Provide core damage evaluation data, where the core damage evaluation data includes the degree of core damage under typical accident sequences of a nuclear power plant and the dose rate information at multiple detection points outside the containment vessel;

[0006] b) Establish a regression model based on a recurrent neural network, train the regression model using the core damage evaluation data, establish a mapping relationship between the dose rate at the detection points, accident variable information, and the degree of core damage, and form a core damage degree evaluation model, where the accident variable information includes the internal cooling condition of the containment vessel, the reactor shutdown duration, and the containment vessel breakage condition;

[0007] c) Provide accident variable information and dose rate information of multiple said detection points obtained through actual measurement, and the core damage degree evaluation model gives the core damage degree evaluation result. This method does not rely on the detection data inside the containment, reduces the risk of misjudging the accident severity caused by the failure of the detection system inside the containment after the accident occurs, and improves the efficiency of core damage degree evaluation.

[0008] Further, in some embodiments, the typical accident sequence of the nuclear power plant in step a) is obtained in the following manner: Provide an integrated analysis program for severe nuclear power plant accidents, provide the accident initiating event, radioactive gas release location, radioactive gas release area, gas deposition environment, and containment damage condition and input them into the integrated analysis program for severe nuclear power plant accidents to obtain the reactor shutdown duration, core damage degree, and dose rate information of multiple said detection points.

[0009] Further, in some embodiments, the process of the integrated analysis program for severe nuclear power plant accidents giving the dose rate information of multiple said detection points includes directly calculating the dose rate information of multiple said detection points according to the input accident conditions, or obtaining the core radionuclide source term according to the input accident conditions and using a gas diffusion model to calculate and obtain the dose rate information of multiple said detection points outside the containment.

[0010] Further, in some embodiments, the detection points include detection points in the containment penetration area and detection points on the outer surface of the containment.

[0011] Further, in some embodiments, the detection points on the outer surface of the containment are isolated from the radiation source term, so that the dose rate is only the radiation passing through the containment wall.

[0012] Further, in some embodiments, there is no interference from internal solid components in the space inside the containment corresponding to the detection points on the outer surface of the containment.

[0013] Further, in some embodiments, the regression model in step b) includes an RNN model, an LSTM model, or a GRU model.

[0014] Further, in some embodiments, step c) further includes the step of providing multiple groups of information of multiple said detection points, and the core damage degree evaluation model respectively gives the core damage degree evaluation results, and the one with the highest damage degree is used as the final evaluation result.

[0015] According to an embodiment of another aspect of the present invention, a computing device is provided. The computing device includes a memory and a processor, wherein the memory stores a computing program, and when the computing program is executed by the processor, it can implement the core damage assessment method based on the dose rate outside the containment provided by any of the foregoing embodiments. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the dose rate detection points in the containment penetration area in an embodiment;

[0017] Figure 2 It is a schematic diagram of the dose rate detection points on the outer surface of the containment in an embodiment.

[0018] The purpose of the above-mentioned drawings is to make a detailed description of the present invention so that those skilled in the art can understand the technical concept of the present invention, rather than aiming to limit the present invention. For the sake of concise expression, the above-mentioned drawings only schematically draw the structures related to the technical features of the present invention, and do not strictly draw the complete device and all details according to the actual proportion. Detailed Embodiments

[0019] The present invention will be further described in detail below through specific embodiments in conjunction with the drawings.

[0020] The mention of "embodiment" in this article means that the specific features, structures or characteristics described in connection with the embodiment may be included in at least one embodiment of this article. The phrase appearing in various positions in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments in this article can be combined with other embodiments without structural conflicts. In the description of this article, the meaning of "a plurality" is at least two.

[0021] An embodiment of one aspect of the present invention provides a method for evaluating core damage based on the dose rate outside the containment. The method includes the following steps:

[0022] First, establish a core damage evaluation database, and obtain core damage evaluation data information such as the degree of core damage and the dose rate at multiple points outside the containment under typical accident sequences of nuclear power plants that may cause core damage.

[0023] In a preferred embodiment, based on the probabilistic safety analysis and engineering judgment of nuclear power plants, a list of the initiating types of typical accidents in nuclear power plants that may lead to core damage is determined. On this basis, specific conditions such as the radioactive gas release location, release area, and gas deposition environment are superimposed. Different accident sequences and variable information such as the corresponding core damage degree and radionuclide source term under the accident sequences are obtained through a general integrated severe accident analysis program for nuclear power plants. In different embodiments, the core damage degree and the dose rate information at multiple points outside the containment can be directly obtained through the integrated severe accident analysis program, or the dose rate information at multiple points outside the containment can be obtained through a gas diffusion model based on the variable information. The dose rate outside the containment includes the gas dose rate and the fluid dose rate. The detection points of the gas dose rate include the detection points in the containment penetration area and the detection points on the outer surface of the containment. The concern point position in the containment penetration area should be as close as possible to the outer surface of the containment. As Figure 1 shown, the dose rate detection point 4 should be set on the surface of the containment concrete wall 2 adjacent to the containment penetration area 3. The concern point position on the outer surface of the containment is as Figure 1 shown. The dose rate detection point 4 should be isolated from the radiation source term to be unaffected by it, and the thickness of the containment concrete wall surface 2 here should be known. The dose rate only comes from the radiation passing through the containment wall from inside the containment. The internal space 1 (γ-ray volume source) of the containment corresponding to the concern point position should have a large enough free volume to ensure the uniform mixing of the gas (the original gas inside the containment and the radioactive gas brought by core damage) and not be disturbed by the solid components inside the containment. If a containment breach occurs near the position of the dose rate detection point 4, the impact of the radioactive gas leaked from the breach on the concern point dose rate needs to be considered. The fluid dose rate mainly comes from the primary coolant sampling system.

[0024] Next, a core damage degree assessment model is established.

[0025] Since the relationship between nuclear power plant accidents and the degree of core damage is complex, the relationship between the dose rate at the detection point and the degree of core damage is not a simple linear relationship. Moreover, key accident variables will further increase the complexity of the corresponding relationship between the dose rate at the detection point and the degree of core damage. It is necessary to establish a correct mapping relationship through a model to extrapolate the data samples in the core damage evaluation database. Based on the data-driven algorithm and the sample data in the core damage evaluation database, a mapping relationship is established between the degree of core damage and the dose rates at multiple detection points outside the containment vessel and the corresponding key accident variables. Among them, the data-driven algorithm is a regression model based on a recurrent neural network. The sample data in the core damage evaluation database is used for model training and performance evaluation to obtain the mapping relationship between the dose rates at multiple detection points outside the containment vessel, the degree of core damage, and the key accident variables. Specifically, the key accident variables include the cooling situation inside the containment vessel, the reactor shutdown duration, and the damage situation of the containment vessel. The specific information can be determined by the typical accident sequences of nuclear power plants.

[0026] Finally, the dose rate information and key accident variable information of multiple detection points outside the containment vessel to be evaluated are input, and the core damage degree model gives the evaluation result of the core damage degree. In some embodiments, the dose rate information of multiple groups of multiple detection points can be input, and the core damage degree evaluation model gives the evaluation results respectively, and the one with the highest damage degree is taken as the final evaluation result. Specifically, in some embodiments, the measurable dose rates outside the containment vessel and the key variable information of the nuclear power plant can be used as input conditions, and the core damage degree evaluation model is used to obtain the core damage degree evaluation result of the nuclear power plant; the measurable dose rates in the containment penetration area and on the outer surface of the containment vessel are respectively used, combined with the key variable information of the nuclear power plant as input conditions, and the core damage degree evaluation model is used to obtain the core damage degree evaluation result of the nuclear power plant; the larger one of the two evaluation results is selected as the real-time core damage evaluation result of the nuclear power plant.

[0027] In a preferred embodiment, a certain type of heavy water reactor is taken as the evaluation object to evaluate the degree of core damage. The steps are as follows:

[0028] In the first step, a core damage evaluation database is established, and the degree of core damage and the dose rate information of multiple detection points outside the containment vessel under the typical accident sequences of nuclear power plants that may cause core damage are obtained.

[0029] Based on the probabilistic safety analysis and engineering judgment of nuclear power plants, a list of initiating event types of typical nuclear power plant accidents that may lead to core damage is determined, including: station blackout accident, pressure tube rupture accident, small break of main pipe accident, large break of main pipe accident, loss of feedwater accident, and complete loss of Class IV power accident, etc. In addition to the initiating event types, the initiating adjustments of the accident sequences should also include conditions such as the release location, release area, and gas deposition environment of radioactive gases. Specifically, for heavy water reactors, the possible release locations of radioactive gases are the pressure tube rupture, the feedwater branch rupture, the main pipe rupture, etc. The gas deposition environment mainly refers to the cooling situation inside the containment. The containment spray and passive cooling systems are one of the important safety systems of the reactor. During the accident, the inert gases and volatile gases generated by core damage are suspended in the atmosphere. When the containment spray system or passive cooling system is activated, due to the wetting effect of cooling on the gas, a large amount of volatile gas nuclides will quickly deposit on the surface of the internal components of the containment. At this time, the radiation dose rate mainly comes from inert gases, and the radiation dose rates inside and outside the containment decrease significantly.

[0030] Due to the shielding effect of the containment concrete wall, the dose rates of radionuclides in most areas outside the containment are low even after a nuclear accident occurs. As Figure 1 shown, only in the vicinity of Penetration Area 3 (such as the air lock) is there a relatively high dose rate.

[0031] Use a general integrated analysis program for severe nuclear power plant accidents to carry out accident sequence calculation and analysis, and give variable information such as the degree of core damage and radionuclide source term under different accident sequences. Then, based on the variable information obtained from the accident sequence analysis, use a gas diffusion model to obtain the dose rates at multiple detection points outside the containment, or directly obtain information such as the degree of core damage and the dose rates at multiple detection points outside the containment under different accident sequences through the integrated analysis program for severe accidents. Consider the radionuclides that contribute significantly to the absorbed dose rate in the analysis, such as inert gas nuclides like krypton and xenon, and volatile gas nuclides like iodine and cesium.

[0032] In the second step, establish an evaluation model for the degree of core damage. Considering that in the same accident sequence, as the shutdown duration increases, the radionuclides gradually decay, resulting in a decrease in the radioactive intensity, which affects the evaluation of the degree of core damage. Therefore, a regression model based on recurrent neural networks (such as RNN model, LSTM model, and GRU model, etc.) is used for the evaluation of the degree of core damage. Use programming tools such as Python / Matlab to build an intelligent evaluation model framework, and use the sample data in the core damage evaluation database to train the model and evaluate its performance, and determine the mapping relationship between the degree of core damage and variables such as the dose rates at multiple detection points outside the containment, the internal cooling situation of the containment, the reactor shutdown duration, and the damage condition of the containment near the dose rate detection points outside the containment.

[0033] In the third step, input the reactor information to be evaluated into the core damage degree evaluation model for evaluation. The input information includes the dose rate information of the detection points outside the containment vessel to be evaluated and the determined key accident variable information (such as the cooling situation inside the containment vessel and the shutdown duration). The core damage degree evaluation model gives the percentage value of the evaluated core damage degree based on the input information. In a further optional embodiment, the evaluation result can be obtained in two ways: using all the measurable dose rates outside the containment vessel and the key variable information of the nuclear power plant as input conditions, and obtaining the evaluation result of the core damage degree of the nuclear power plant through the core damage degree evaluation model; respectively using the measurable dose rates in the penetration area of the containment vessel and on the outer surface of the containment vessel, combined with the key variable information of the nuclear power plant as input conditions, and obtaining the evaluation result of the core damage degree of the nuclear power plant through the core damage degree evaluation model; selecting the larger value from the two evaluation results as the real-time core damage evaluation result of the nuclear power plant.

[0034] The above method can intelligently evaluate the core damage degree based on the dose rate outside the containment vessel, reduce the risks and uncertainties brought to the core damage evaluation by the failure of the detection system inside the containment vessel under accident conditions, improve the automation degree of nuclear power safety performance evaluation, simplify the core damage degree evaluation process, and thus improve the efficiency of nuclear accident emergency response decision-making.

[0035] According to an embodiment of another aspect of the present invention, a computing device is provided. The computing device can be a general computing device such as a computer, or a computing platform specifically built with a memory and a processor, or a cloud computing device, etc. A computing program for core damage evaluation is stored in the memory of the computing device. When the computing program is executed by the processor, it can implement the core damage evaluation method based on the dose rate outside the containment vessel provided in the foregoing embodiments. The computing device can be integrated into the nuclear power plant control system to perform real-time detection and evaluation of the operating state of the nuclear power plant, or can be automatically started after an accident to evaluate the severity of the accident.

[0036] The purpose of the above embodiments is to further elaborate on the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope disclosed in the present invention, optimizing or replacing the method steps involved, and combining the implementation manners in different embodiments without principle conflicts all fall within the protection scope of the present invention.

Claims

1. A core damage assessment method based on the dose rate outside the containment vessel, characterized in that, It includes the following steps: a) Providing core damage assessment data, which includes the core damage degree under typical accident sequences of nuclear power plants and the dose rate information at multiple detection points outside the containment; b) Establishing a regression model based on a recurrent neural network, training the regression model using the core damage assessment data, establishing the mapping relationship between the dose rate at the detection points, accident variable information, and the core damage degree, and forming a core damage degree assessment model, where the accident variable information includes the internal cooling condition of the containment, the reactor shutdown duration, and the containment breakage condition; c) Providing accident variable information and the dose rate information at multiple detection points obtained through actual measurement, and obtaining the core damage degree assessment result from the core damage degree assessment model.

2. The core damage assessment method based on the dose rate outside the containment according to claim 1, wherein, The typical accident sequences of the nuclear power plant in step a) are obtained in the following way: providing an integrated analysis program for severe accidents in nuclear power plants, providing the accident initiating event, radioactive gas release location, radioactive gas release area, gas deposition environment, and containment breakage condition and inputting them into the integrated analysis program for severe accidents in nuclear power plants to obtain the reactor shutdown duration, core damage degree, and dose rate information at multiple detection points.

3. The core damage assessment method based on the dose rate outside the containment according to claim 2, wherein The process of the integrated analysis program for severe accidents in nuclear power plants giving the dose rate information at multiple detection points includes directly calculating the dose rate information at multiple detection points according to the input accident conditions, or obtaining the core radionuclide source term according to the input accident conditions and calculating and obtaining the dose rate information at multiple detection points outside the containment using a gas diffusion model.

4. The method for evaluating core damage based on the dose rate outside the containment according to claim 1 or 2, characterized in that, The detection points include detection points in the containment penetration area and detection points on the outer surface of the containment.

5. The method for core damage assessment based on the dose rate outside the containment according to claim 4, wherein The detection points on the outer surface of the containment are isolated from the radiation source term, so that the dose rate is only the radiation passing through the containment wall.

6. The core damage assessment method based on the dose rate outside the containment according to claim 4, wherein There is no interference from internal solid components in the space inside the containment corresponding to the detection points on the outer surface of the containment.

7. The core damage assessment method based on the external containment dose rate according to claim 1 or 2, characterized in that The regression model in step b) includes an RNN model, an LSTM model, or a GRU model.

8. The method for evaluating core damage based on the dose rate outside the containment according to claim 1 or 2, characterized in that In step c), there is also a step of providing multiple sets of dose rate information at multiple detection points, and the core damage degree assessment model respectively gives the core damage degree assessment results, and the one with the highest damage degree is used as the final assessment result.

9. A computing device, comprising a memory and a processor, characterized in that, The memory stores a calculation program, and when the calculation program is executed by the processor, it can implement the core damage assessment method based on the dose rate outside the containment as described in any one of claims 1 to 8.

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