Real-time diffusion calculation method for radioactive materials in complex nuclear power plant buildings after accidents

Abstract

The present invention provides a method for calculating the real-time diffusion of radioactive materials in a complex power plant building following a power plant accident, comprising the following steps: Step S1: preprocessing power plant geometry data and local meteorological data; Step S2: determining the data content format, and if the format is correct, proceeding to Step S3; Step S3: inputting the data content into a power plant compartment air convection model for calculation, thereby obtaining a power plant compartment air convection calculation result; Step S4: using the power plant compartment air convection calculation result and the power plant geometry data as inputs for calculating the transport and deposition of fission product aerosols in the power plant compartment, calculating the transport and deposition of fission product aerosols, and obtaining the concentration distribution of fission products in the power plant compartment. The method provided by the present invention implements air convection calculation and fission product diffusion calculation, obtaining the distribution of fission products in the compartment in real time.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear power simulation, and in particular to a method for calculating the real-time diffusion of radioactive materials in a complex plant building caused by an accident in a nuclear power plant. Background Art

[0002] In the event of a serious accident at a nuclear power plant, radioactive materials (including gases and aerosols) will leak and release, and the radioactive materials will undergo complex processes such as diffusion, sedimentation, and attenuation in the complex plant. As the accident progresses, the calculation data and monitoring data of nuclear accident sources are limited. How to accurately and quickly evaluate the dynamic response and distribution of radioactive materials in the plant will greatly affect the implementation of mitigation measures and decision-making support for emergency response personnel in the plant.

[0003] Traditional simulation calculations based on severe accident analysis software programs can handle simple calculation models. However, for complex models of nuclear power plants (such as auxiliary plant calculations), when the number of simulated compartments exceeds hundreds, the simulation limit of this calculation method has been reached, and it cannot meet the needs of real-time calculations, which greatly affects the accurate and rapid response and decision support of nuclear emergencies in the event of an accident. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects described in the prior art, thereby providing a method for calculating the real-time diffusion of radioactive materials in a complex plant building caused by a nuclear power plant accident. The method realizes air convection calculation and fission product diffusion calculation, and obtains the distribution of fission products in the compartment in real time.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for calculating the real-time diffusion of radioactive materials in a complex plant building during a nuclear power plant accident includes the following steps:

[0007] Step S1: Preprocessing plant geometry data and local meteorological data;

[0008] Step S2: Determine the data content format. If the format is correct, proceed to step S3.

[0009] Step S3: the data content is input into the factory compartment air convection model for calculation to obtain the factory compartment air convection calculation result;

[0010] Step S4: using the air convection calculation results of the plant compartment and the plant geometry data as inputs for the calculation of fission product aerosol transport and deposition in the plant compartment, calculating the fission product aerosol transport and deposition, and obtaining the concentration distribution of fission products in the plant compartment.

[0011] The plant compartment air convection model is preprocessed in combination with the plant geometry data and local meteorological data. After the error judgment is completed, it enters the plant compartment air convection module to perform air convection calculation, instantiates the plant geometry model and calls the calculation function of the calculation compartment air convection, and finally obtains the plant compartment air convection calculation result.

[0012] The air convection model of the plant compartment is: Where,

[0013]

[0014] In step S4, two calculation modes are used according to whether the HVAC system is put into operation. In combination with the plant geometry data file and the air convection calculation results of the plant compartments, a rapid diffusion calculation of fission products is performed to realize the aerosol transport and deposition simulation of fission products, and the concentration distribution of fission products in the plant compartments is obtained in real time.

[0015] In the presence of a HVAC system, the plant geometry data file is read to perform fission product diffusion calculations.

[0016] Among them, the change in the total amount of radioactive substances meets the

[0017] In the absence of a heating and ventilation system, the plant geometry data file and the air convection calculation results of the plant compartments are read to perform a rapid diffusion calculation of fission products.

[0018] In step S4, the aerosol transport and deposition of fission products are calculated by combining the accident source data and isotope-related data.

[0019] Compared with the existing technology, the real-time diffusion calculation method of radioactive materials in a complex plant building in a nuclear power plant provided by the present invention has the following beneficial effects:

[0020] The present invention establishes an air convection model and a fission product diffusion model, and combines it with nuclear accident source data to quickly and accurately obtain the diffusion, sedimentation and attenuation processes of radioactive substances in complex plant buildings, as well as the concentration distribution, providing a reference and basis for emergency personnel dose assessment, accident emergency response, and emergency decision-making.

[0021] The present invention combines the actual operating requirements of nuclear power plants in accident situations and comprehensively considers both the presence and absence of a HVAC system during the radioactive material diffusion calculation process. In the case of no HVAC system, the air flow in the plant is caused by leakage and air infiltration from the environment. In the case of an HVAC system, the air flow is driven by the operating HVAC system to realize the fission product diffusion calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A flow chart for calculating the diffusion of radioactive substances within a plant compartment provided by an embodiment of the present invention;

[0024] Figure 2 A schematic diagram of the leakage location of a simple factory building provided by an embodiment of the present invention;

[0025] Figure 3 This is a flow chart of air convection calculation provided by an embodiment of the present invention;

[0026] Figure 4 This is a flowchart of the fission product diffusion calculation provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following is further explained in detail through specific implementation methods.

[0028] like Figures 1 to 4 As shown, the present invention provides a method for calculating the real-time diffusion of radioactive materials in a complex plant building caused by a nuclear power plant accident, including air convection calculation and fission product diffusion calculation, and specifically includes the following steps:

[0029] Step S1: Preprocessing plant geometry data and local meteorological data;

[0030] Step S2: Determine the data content format. If the format is correct, proceed to step S3.

[0031] Step S3: inputting the data content into the factory compartment air convection model for calculation to obtain the factory compartment air convection calculation result;

[0032] Step S4: The air convection calculation results of the plant compartment and the plant geometry data are used as inputs for the calculation of fission product aerosol transport and deposition in the plant compartment. Combined with the accident source data and isotope-related data, the fission product aerosol transport and deposition are calculated to obtain the concentration distribution of fission products in the plant compartment.

[0033] Among them, the factory compartment air convection model is based on the law of conservation of mass. It is preprocessed in combination with the factory geometry data and local meteorological data. After the error judgment is completed, it enters the factory compartment air convection module to perform air convection calculation. The factory geometry model is instantiated and the calculation function of the calculation compartment air convection is called. Finally, the factory compartment air convection calculation result is obtained.

[0034] In step S4, based on the law of conservation of mass of fission products, two calculation modes with and without the HVAC system are comprehensively considered. Combined with the plant geometry data file and the air convection calculation results of the plant compartments, the rapid diffusion calculation of fission products is performed to realize the fission product aerosol transport and deposition simulation, and finally the concentration distribution of fission products in the plant compartments is obtained in real time.

[0035] like Figure 2 As shown, the leakage gaps in the factory are assumed to be distributed at the lowest point (near the ground) and the highest point (near the roof) of the factory. Considering the height of the factory, the gap locations can be considered to be at the ground and the roof, so the difference H1 between the upper and lower gaps is the height of the factory. The cross-sectional areas of the leakage gaps are A1, A2, A3, and A4, respectively. Their sum (i.e., the total cross-sectional area of ​​the factory gaps) is the effective or equivalent leakage area (ELA) of the factory, which is a design parameter of the factory. Assuming that A1 to A4 are equal, and assuming that they are all equal to A, the ratio of the gap area of ​​each compartment to the total cross-sectional area is equal to the ratio of the volume of each compartment to the sum of their volumes. Air convection between the environment and the factory has two driving forces: temperature difference and wind speed. It is not difficult to find that the assumption results in maximizing air convection between the factory and the environment.

[0036] The calculation method (model) for air convection between plant compartments is as follows:

[0037] According to the law of conservation of mass, the following air flow equation is obtained:

[0038]

[0039] Where,

[0040] For internal compartments (i.e. compartments not connected to the containment or the environment),

[0041]

[0042] Where,

[0043]

[0044] The amount of air entering the plant from the containment and the environment is very small, and the volume of the compartments in the plant is so large that the most conservative estimate of the air temperature change in the plant is far less than 0.01K. Therefore, the temperature of all compartments in the plant can be considered to be constant and the same, where:

[0045]

[0046]

[0047] The fission product diffusion calculation with the HVAC system turned off (the plant compartment fission product aerosol transport and deposition model or the fission product diffusion model) is as follows:

[0048] The fission products diffuse in the plant along with the air flow. The air volume flow rate between the compartments is obtained in the air convection calculation.

[0049]

[0050] Q i,j : air volume flow rate [m3 / s]; if it flows from compartment j to compartment i, its value is positive, otherwise it is negative;

[0051] T i : temperature of compartment i (K), According to the law of conservation of fission product mass, the mass of fission products in compartment i can be obtained:

[0052]

[0053]

[0054] Where,

[0055] M is the mass of fission products in the air inside the containment (kg);

[0056] M i is the mass of fission products in the space of compartment i (kg);

[0057] M s,i Mass of fission products in the air inside the containment (kg)

[0058] F i is the mass flow rate of fission products flowing into or out of compartment i (kg / s);

[0059] V i The volume in compartment i (m 3 );

[0060] A i is the floor area in compartment i (m 2 );

[0061] u s is the fission product settling velocity (m / s);

[0062] Q i is the air flow rate from the environment into the compartment (m 3 / s);

[0063] is the fractional leakage rate from the containment into the compartment (1 / s).

[0064] Specifically, when the HVAC system is operating, the fission product diffusion calculation (model) of the HVAC system operation makes the following assumptions:

[0065] (1) All compartments are connected to the HVAC system.

[0066] (2) The volumetric flow rates of all compartments to the HVAC system divided by their respective volumes are the same, and these volumetric flow rates are also equal to the volumetric flow rates returning from the HVAC system to each compartment.

[0067] (3) Air convection between the HVAC system and the compartments does not cause changes in air quality (AirMasses).

[0068] (4) The fission products drawn into the HVAC system from the compartments connected to the containment are mixed in proportion to the corresponding air flow rates and then redistributed to all compartments.

[0069] For compartment i, the change in the total amount of radioactive material satisfies:

[0070]

[0071] Where,

[0072] is the leakage rate from containment to compartment i ( / s);

[0073] m a is the total mass of radioactive materials in the containment (kg);

[0074] n is the total number of compartments;

[0075] V i is the volume of compartment i (m 3 );

[0076] M i is the total mass of radioactive material in compartment i (kg);

[0077] λ i is the ratio of radioactive material flowing from the HVAC system to compartment i (the ratio of radioactive material to the total radioactive material flowing from the HVAC system) ( / s);

[0078] λ is the ratio of radioactive material flow from compartment i to the HVAC system (the ratio of radioactive material to the radioactive material in compartment i) ( / s). It is recommended to use the HVAC design parameters, and the default value is 1 / 300;

[0079] Ms,i is the mass of fission products deposited on the floor in compartment i (kg);

[0080] u s is the fission product settling velocity (m / s).

[0081] Figure 3 The air convection calculation method and process are described. The calculation method first preprocesses the plant geometry data and local meteorological data, and then performs error checking on the content and format of the input data file through the error judgment function. If there is an error, an error report is generated. If there is no error, the corresponding database file is generated. After the preprocessing and error judgment are completed, the air convection module of the plant compartment is entered to perform air convection calculation, the plant geometry model is instantiated, and the calculation function of the calculation compartment air convection is called. Finally, the calculation result of the plant compartment air convection is obtained.

[0082] Figure 4 The fission product diffusion calculation method and process are described. The calculation method first preprocesses the serious accident source data and radioactive isotope data, and uses the error judgment function to check the content and format of the input data file for errors. If there is an error, an error report is generated. If there is no error, a corresponding database file is generated. After the preprocessing and error judgment are completed, two calculation modes are considered, one with or without the HVAC system. When the HVAC system is in place, the plant geometry data file is read to perform fission product diffusion calculations; when the HVAC system is not in place, the plant geometry data file and the air convection calculation results of the plant compartment are read to perform rapid fission product diffusion calculations, realize fission product aerosol transport and deposition simulation, and finally obtain the concentration distribution of fission products in the plant compartment in real time.

[0083] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention are intended to be covered by the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection of the claims.

Claims

1. A method for calculating the real-time diffusion of radioactive materials in a complex plant building during a nuclear power plant accident, characterized in that: The following steps are involved: Step S1: Preprocessing plant geometry data and local meteorological data; Step S2: Determine the data content format. If the format is correct, proceed to step S3. Step S3: The data content is input into the plant compartment air convection model for calculation to obtain the plant compartment air convection calculation result; the plant compartment air convection model is preprocessed in combination with the plant geometry data and local meteorological data. After the error judgment is completed, the plant compartment air convection module is entered to perform air convection calculation, the plant geometry model is instantiated and the calculation function of the calculation compartment air convection is called, and finally the plant compartment air convection calculation result is obtained; the calculation function of the calculation compartment air convection is: According to the law of conservation of mass, the following air flow equation is obtained: Where, For the internal compartments, Where, Among them, the air convection model of the plant compartment is Where, Where A i,j is the area of ​​the link between compartment i and compartment j, C d is the flow coefficient, ρ i , ρ j are the air densities of compartment i and compartment j, R a is the ideal gas constant, T i is the temperature of compartment i, T o is the ambient temperature, is the air flow rate from the containment into compartment i, m a The air quality in the containment, ΔT is the absolute value of the temperature difference between the environment and the plant, H1 is the plant elevation above the baseline, ΔC p is the average surface pressure coefficient difference, ρ o is the air density outside the factory, A i is one quarter of the equivalent leakage area of ​​compartment i, and V is the wind speed; Step S4: using the air convection calculation results of the plant compartment and the plant geometry data as inputs for the calculation of fission product aerosol transport and deposition in the plant compartment, calculating the fission product aerosol transport and deposition, and obtaining the concentration distribution of fission products in the plant compartment.

2. The method for calculating the real-time diffusion of radioactive substances in a complex plant building caused by a nuclear power plant accident according to claim 1 is characterized in that: In step S4, two calculation modes are used according to whether the HVAC system is put into operation. In combination with the plant geometry data file and the air convection calculation results of the plant compartments, a rapid diffusion calculation of fission products is performed to realize the aerosol transport and deposition simulation of fission products, and the concentration distribution of fission products in the plant compartments is obtained in real time.

3. The method for calculating the real-time diffusion of radioactive substances in a complex plant building caused by a nuclear power plant accident according to claim 2, characterized in that: In the presence of a HVAC system, the plant geometry data file is read to perform fission product diffusion calculations.

4. The method for calculating the real-time diffusion of radioactive substances in a complex plant building caused by a nuclear power plant accident according to claim 3 is characterized in that: The change in the total amount of radioactive material meets the is the leakage rate from containment to compartment i, m a is the total mass of radioactive materials in the containment, λ i is the ratio of radioactive material flow from the HVAC system to compartment i, λ is the ratio of radioactive material flow from compartment i to the HVAC system, and n is the total number of compartments.

5. The method for calculating the real-time diffusion of radioactive substances in a complex plant building caused by a nuclear power plant accident according to claim 2, characterized in that: In the absence of a heating and ventilation system, the plant geometry data file and the air convection calculation results of the plant compartments are read to perform a rapid diffusion calculation of fission products.

6. The method for calculating the real-time diffusion of radioactive substances in a complex plant building caused by a nuclear power plant accident according to claim 1 is characterized in that: In step S4, the aerosol transport and deposition of fission products are calculated by combining the accident source data and isotope-related data.

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