Source analysis method and system for reactor loss of coolant accident

Abstract

The present invention relates to a source term analysis method and system for reactor loss of coolant accident, the source term analysis method includes: obtaining the decay constant and sedimentation factor of radioactive nuclides, and obtaining the containment leakage rate in real time, and calculating the concentration of radioactive nuclides in the containment during the transient process; calculating the current concentration of radioactive nuclides in the cabin according to the ventilation rate of the cabin, the current containment leakage rate, the concentration of radioactive nuclides in the containment at the previous moment, and the concentration of radioactive nuclides in the cabin at the previous moment; obtaining the filtration efficiency of the cabin ventilation system for radioactive nuclides, and calculating the concentration of radioactive nuclides released to the environment during the current period; calculating the total amount of radioactive nuclides released to the environment during the entire accident. Through this technical solution, when a reactor (such as a small offshore reactor) loses coolant, the accuracy of key inputs for assessing the radioactive consequences of the accident on the public is improved, and accurate data support is provided for safety analysis and environmental impact assessment of nuclear power plants.

Description

Technical Field

[0001] The present invention relates to the field of safety analysis of nuclear power plants, and in particular to a source term analysis method and system for a reactor loss of coolant accident. Background Art

[0002] The containment is an important safety facility in nuclear power plants and the last barrier to prevent the release of radioactive substances into the atmosphere. In order to prevent the radioactive substances released from the core from leaking into the environment, the containment of existing large nuclear power plants is designed as a double-layer structure. However, due to the particularity of offshore nuclear power plants, they need to be miniaturized based on existing large nuclear power plants. The double-layer containment structure is relatively complex and is not conducive to the miniaturization of the containment of offshore nuclear power plants. Therefore, the containment of offshore nuclear power plants is designed as a single-layer structure.

[0003] At present, although there are guidelines for the analysis of source items of design basis accidents of pressurized water reactor nuclear power plants, when conducting source item analysis of loss of coolant accidents according to these guidelines, it is necessary to consider the release of cladding gaps, the removal of the spray system or natural deposition mechanism in the containment, the analysis assumptions of the containment leakage rate, the assumptions of radioactive release under the double containment design, etc. However, since offshore nuclear power plants (small types) do not have double containments, the radioactive nuclides in the containment leak out and are released into the environment through the cabin, and the guidelines do not directly provide relevant analysis methods or assumptions. Moreover, for the containment leakage rate, the assumption given in the guidelines is that the containment leakage rate under the containment design pressure is used within 24 hours, and after 24 hours, it is considered to be 50% of the design value, without considering the transient change process of the containment pressure after the accident. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a source term analysis method and system for a reactor loss of coolant accident in view of the defect that the existing source term analysis method in the prior art is not applicable to offshore nuclear power plants.

[0005] The technical solution adopted by the present invention to solve the technical problem is: construct a source term analysis method for a reactor loss of coolant accident, and for a specific radioactive nuclide, perform the following steps:

[0006] Step S10. Obtain the decay constant and sedimentation factor of the radioactive nuclide, and obtain the containment leakage rate in real time, and calculate the radioactive nuclide concentration in the containment during the transient process according to the decay constant, the sedimentation factor and the real-time containment leakage rate;

[0007] Step S20. Calculate the current radionuclide concentration in the cabin according to the cabin ventilation rate, the current containment leakage rate, the radionuclide concentration in the containment at the previous moment, and the radionuclide concentration in the cabin at the previous moment;

[0008] Step S30. Obtain the filtration efficiency of the cabin's ventilation system for the radioactive nuclides, and calculate the concentration of radioactive nuclides released into the environment during the current period based on the ventilation rate, the filtration efficiency, and the current concentration of radioactive nuclides in the cabin;

[0009] Step S40: Calculate the total amount of radionuclides released into the environment during the entire accident period based on the concentrations of radionuclides released into the environment in multiple different time periods.

[0010] Preferably, there is a cabin outside the containment. In step S10, the concentration of radionuclides in the containment during the transient process is calculated according to formula 1:

[0011]

[0012] Among them, A i (t) is the concentration of radionuclides in the containment during the transient process, λ ci is the decay constant of radionuclide i, λ di is the sedimentation factor of radionuclide i, L m is the containment leakage rate.

[0013] Preferably, in step S20, the current radionuclide concentration in the cabin is calculated according to Formula 2:

[0014]

[0015] Among them, C i (t) is the current radionuclide concentration in the cabin, C i,0 is the concentration of radionuclides in the cabin at the previous moment, A i，0 is the concentration of radionuclides in the containment at the previous moment, L j is the ventilation rate of the cabin.

[0016] Preferably, in step S30, the concentration of radionuclides released into the environment during the current period is calculated according to Formula 3:

[0017]

[0018] Among them, Q n (t n ,t n+1 ) is the concentration of radionuclides released into the environment during the current period, ff i is the filtration efficiency of the ventilation system for radionuclide i.

[0019] Preferably, in step S40, the total amount of the radionuclides released into the environment during the entire accident period is calculated according to Formula 4:

[0020]

[0021] Among them, Q n,total is the total amount of radionuclide i released into the environment during the entire accident period.

[0022] Preferably, there are multiple independent compartments outside the containment. In step S10, the radionuclide concentration inside the containment during the transient process is calculated according to Formula 5:

[0023]

[0024] Among them, A i (t) is the concentration of radionuclides in the containment during the transient process, λ ci is the decay constant of radionuclide i, λ di is the sedimentation factor of radionuclide i, L m,k is the leakage rate from the containment to the kth compartment.

[0025] Preferably, in step S20, the current radionuclide concentration in the cabin k is calculated according to Formula 6:

[0026]

[0027] Among them, C i,k (t) is the current radionuclide concentration in the kth compartment, C i,k,0 is the radionuclide concentration in the kth cabin at the previous moment, A i，0 is the concentration of radionuclides in the containment at the previous moment, L j,k is the ventilation rate of the kth cabin.

[0028] Preferably, in step S30, the concentration of radionuclides released into the environment from the kth cabin in the current period is calculated according to Formula 7:

[0029]

[0030] Among them, Q n,k (t n ,t n+1 ) is the concentration of radionuclides released into the environment from the kth compartment in the current period, ff i,k is the filtration efficiency of the ventilation system of the kth cabin for radionuclide i.

[0031] Preferably, in step S40, the total amount of the radioactive nuclides released into the environment during the entire accident period is calculated according to Formula 8 and Formula 9:

[0032]

[0033]

[0034] Among them, Q n,k,total Q is the total amount of radionuclide i released to the environment from the kth compartment during the entire accident period, n,total is the total amount of radionuclide i released into the environment during the entire accident period.

[0035] The present invention also constructs a source term analysis system for a reactor loss of coolant accident, comprising a processor and a memory storing a computer program, wherein the processor implements the steps of the above-mentioned source term analysis method for a reactor loss of coolant accident when executing the computer program.

[0036] In the technical solution provided by the present invention, a complete source term analysis method for loss of coolant accident is constructed in view of the design characteristics of the containment and cabin of the offshore nuclear power plant (small type). The source term analysis method takes into account the change of the containment leakage rate caused by the pressure change in the containment after the accident, and calculates the concentration of radionuclides in the following three stages in different time periods: release into the containment; release from the containment into the surrounding cabin; release from the surrounding cabin into the environment, and finally, the total amount of radionuclides released to the environment during the entire accident is calculated based on the concentration of radionuclides released into the environment in all time periods during the accident. Therefore, when a loss of coolant accident occurs in a reactor, especially when a loss of coolant accident occurs in an offshore nuclear power plant (small type), the accuracy of the key input for evaluating the radioactive consequences of the accident on the public is improved, and accurate data support is provided for the safety analysis and environmental impact assessment of nuclear power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0038] Figure 1 It is a schematic diagram of source term release when a loss of coolant accident occurs in a small offshore reactor;

[0039] Figure 2 It is a flow chart of Example 1 of the source term analysis method for reactor loss of coolant accident of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] First of all, when a loss of coolant accident (LOCA) occurs in a small offshore reactor, the radionuclides in the primary coolant and the damaged fuel will be released into the containment, and then released into the surrounding cabins through leakage, and released into the environment through the cabin ventilation system and chimney, causing radiation hazards to the public and organisms. Calculating the activity of radionuclides released into the environment is a key input for assessing the radioactive consequences of an accident on the public, and is a key focus of nuclear power plant safety analysis and environmental impact assessment.

[0042] like Figure 1 As shown in the figure, after a LOCA occurs, the initial radionuclides in the coolant are released into the atmosphere in the containment through the breach. When the fuel is damaged, the radionuclides in the gaps between the damaged fuel rod cladding are released into the coolant, and then released into the containment through the breach. Moreover, after a LOCA occurs, the pressure in the containment rises rapidly, and the radionuclides in the atmosphere in the containment are released into the surrounding compartments in the form of containment leakage, and then released into the environment through the ventilation system and chimney.

[0043] This application constructs a complete LOCA source term method based on the design characteristics of the containment and cabin of the offshore small reactor, taking into account the change in the containment leakage rate caused by the pressure change in the containment after the accident, and calculates the change in the concentration of radionuclides in the containment, the change in the concentration of radionuclides in the cabin, and the release to the environment.

[0044] Figure 2 1 is a flow chart of a first embodiment of a source term analysis method for a reactor loss of coolant accident according to the present invention. In the source term analysis method of this embodiment, for a specific radionuclide, the following steps are performed:

[0045] Step S10. Obtain the decay constant and sedimentation factor of the radioactive nuclide, and obtain the containment leakage rate in real time, and calculate the radioactive nuclide concentration in the containment during the transient process according to the decay constant, the sedimentation factor and the real-time containment leakage rate;

[0046] In this step, the decay constant of the radionuclide is a known value, and its unit is s -1 The sedimentation factor of the radionuclide is related to environmental factors such as temperature and humidity in the containment, and its unit is s -1 The containment leakage rate can be obtained by real-time calculation of the real-time detection data of the temperature and humidity sensor, the pressure sensor inside the containment, the atmospheric pressure sensor outside the containment, and the compressed air flow meter. The unit is s -1, that is, the calculated containment leakage rate is the containment leakage rate in the transient process. Moreover, when a loss of coolant accident occurs, the pressure inside the shell increases rapidly, and the radioactive nuclides in the atmosphere inside the containment are released to the surrounding compartments through the containment leakage, so the containment leakage rate also increases.

[0047] Step S20. Calculate the current radionuclide concentration in the cabin according to the cabin ventilation rate, the current containment leakage rate, the radionuclide concentration in the containment at the previous moment, and the radionuclide concentration in the cabin at the previous moment;

[0048] Step S30. Obtain the filtration efficiency of the cabin's ventilation system for the radioactive nuclides, and calculate the concentration of radioactive nuclides released into the environment during the current period based on the ventilation rate, the filtration efficiency, and the current concentration of radioactive nuclides in the cabin;

[0049] Step S40: Calculate the total amount of radionuclides released into the environment during the entire accident period based on the concentrations of radionuclides released into the environment in multiple different time periods.

[0050] In a specific embodiment, there is only one compartment outside the containment, that is, the radioactive nuclides in the containment are released to only one compartment in the form of leakage from the containment. In this case, the source term analysis steps of the radioactive nuclides are specifically as follows:

[0051] In step S10 of this embodiment, at time 0 after the loss of coolant accident, it is conservatively assumed that all the reactor coolant is sprayed into the containment atmosphere, and the radioactive nuclides in the coolant are evenly mixed with the containment atmosphere. In addition, it is conservatively assumed that LOCA causes damage to the fuel cladding of the entire core. After the fuel is damaged, the cladding release phase is entered. It is assumed that the radioactive nuclides released in this phase are released into the coolant, instantly enter the containment atmosphere and are evenly mixed, and the retention of radioactive nuclides by the coolant is not considered. The distribution of fission products in the fuel is considered in the analysis to determine the conservative share of fission products in the cladding gap. After the aerosol and elemental iodine are released into the containment, the natural sedimentation process in the containment is conservatively considered. The removal of radioactive nuclides by the suppression pool is not considered. In the transient process, the decay process of fission products in the containment is considered. The concentration A of fission products (radioactive nuclides) in the containment i (t) is obtained by solving the differential equation, that is, the concentration of radionuclides in the containment during the transient process is calculated according to Formula 1:

[0052]

[0053] Among them, A i (t) is the concentration of radionuclides in the containment during the transient process, λ ci is the decay constant of radionuclide i, λ diis the sedimentation factor of radionuclide i, L m is the containment leakage rate.

[0054] In step S20 of this embodiment, after the accident occurs, the containment pressure rises rapidly, and the radionuclides in the atmosphere of the containment are released to the surrounding cabins in the form of containment leakage, and the containment leakage rate in the transient process is calculated according to the pressure change in the containment. According to the containment leakage rate and the radionuclides concentration in the containment, the radionuclides concentration leaking to the surrounding cabins can be calculated. Specifically, before the loss of coolant accident occurs, it is assumed that the normal column of the ventilation system of the surrounding cabins is continuously operated at the maximum ventilation flow rate. After the loss of coolant accident occurs, it is conservatively assumed that the radionuclides leaking from the containment to the surrounding cabins are all released into the environment, and then the normal column of the cabin ventilation system is isolated, and the accident ventilation column is started and operated at the maximum ventilation flow rate. The radionuclides leaking from the containment into the cabin are filtered by the accident column of the cabin ventilation system and discharged into the environment. The filtration of radionuclides is conservatively considered according to the design of the ventilation system filter. Therefore, for the surrounding cabins, the change in the concentration of radionuclides in the cabin can be calculated according to the radionuclides concentration leaking from the containment and the cabin ventilation flow rate, that is, the current radionuclides concentration in the cabin is calculated according to Formula 2:

[0055]

[0056] Among them, C i (t) is the current radionuclide concentration in the cabin, C i,0 is the concentration of radionuclides in the cabin at the previous moment, A i，0 is the concentration of radionuclides in the containment at the previous moment, L j is the ventilation rate of the cabin.

[0057] In step S30 of this embodiment, the current time period (t n ,t n+1 ) Radionuclide concentration Q to the environment n (t n ,t n+1 ), that is, the concentration of radionuclides released into the environment during the current period is calculated according to Formula 3:

[0058]

[0059] Among them, Q n (t n ,t n+1 ) is the concentration of radionuclides released into the environment during the current period, ff i is the filtration efficiency of the ventilation system for radionuclide i.

[0060] In step S40 of this embodiment, the release amount Q of different time periods is n (t n ,t n+1 ) can be summed to obtain the total amount of radioactive release of the radionuclide to the environment during the entire accident period Q n,total , that is, according to the

[0061] Formula 4 calculates the total amount of radionuclides released into the environment during the entire accident period:

[0062]

[0063] Among them, Q n,total is the total amount of radionuclide i released into the environment during the entire accident period.

[0064] In another specific embodiment, there are multiple compartments outside the containment, that is, the radioactive nuclides in the containment are released to the multiple compartments respectively in the form of containment leakage. The source term analysis calculation steps in this case are similar to those in one compartment, specifically:

[0065] In step S10 of this embodiment, the radionuclide concentration in the containment of the transient process is calculated according to Formula 5:

[0066]

[0067] Among them, A i (t) is the concentration of radionuclides in the containment during the transient process, λ ci is the decay constant of radionuclide i, λ di is the sedimentation factor of radionuclide i, L m,k is the leakage rate from the containment to the kth compartment.

[0068] In step S20 of this embodiment, the current radionuclide concentration in the cabin k is calculated according to Formula 6:

[0069]

[0070] Among them, C i,k (t) is the current radionuclide concentration in the kth compartment, C i,k,0 is the radionuclide concentration in the kth cabin at the previous moment, A i，0 is the concentration of radionuclides in the containment at the previous moment, L j,k is the ventilation rate of the kth cabin.

[0071] In step S30 of this embodiment, the concentration of radionuclides released into the environment from the kth cabin in the current period is calculated according to Formula 7:

[0072]

[0073] Among them, Q n,k (t n ,t n+1 ) is the concentration of radionuclides released into the environment from the kth compartment in the current period, ff i,k is the filtration efficiency of the ventilation system of the kth cabin for radionuclide i.

[0074] In step S40 of this embodiment, the total amount of radionuclides released to the environment during the entire accident period is calculated according to Formula 8 and Formula 9:

[0075]

[0076]

[0077] Among them, Q n,k,total Q is the total amount of radionuclide i released to the environment from the kth compartment during the entire accident period, n,total is the total amount of radionuclide i released into the environment during the entire accident period.

[0078] The present invention also constructs a source term analysis system for a reactor loss of coolant accident, comprising a processor and a memory storing a computer program, wherein the processor implements the steps of the above-mentioned source term analysis method for a reactor loss of coolant accident when executing the computer program.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A source term analysis method for reactor loss of coolant accident, characterized in that: For a specific radionuclide, perform the following steps: Step S10. Obtain the decay constant and sedimentation factor of the radioactive nuclide, and obtain the containment leakage rate in real time, and calculate the radioactive nuclide concentration in the containment during the transient process according to the decay constant, the sedimentation factor and the real-time containment leakage rate; Step S20. Calculate the current radionuclide concentration in the cabin according to the cabin ventilation rate, the current containment leakage rate, the radionuclide concentration in the containment at the previous moment, and the radionuclide concentration in the cabin at the previous moment; Step S30. Obtain the filtration efficiency of the cabin's ventilation system for the radioactive nuclides, and calculate the concentration of the radioactive nuclides released into the environment during the current period based on the ventilation rate, the filtration efficiency, and the current concentration of the radioactive nuclides in the cabin; Step S40. Calculate the total amount of radionuclides released into the environment during the entire accident period according to the concentrations of radionuclides released into the environment during multiple different time periods; There is a cabin outside the containment. In step S10, the concentration of radioactive nuclides in the containment during the transient process is calculated according to formula 1: Formula 1 in, is the radionuclide concentration in the containment during the transient process, For radionuclides The decay constant of For radionuclides The sedimentation factor, is the containment leakage rate; In step S20, the current radionuclide concentration in the cabin is calculated according to formula 2: Formula 2 in, is the current radionuclide concentration in the cabin, is the concentration of radionuclides in the cabin at the previous moment, is the concentration of radionuclides in the containment at the previous moment, is the ventilation rate of the cabin; In step S30, the concentration of radionuclides released into the environment during the current period is calculated according to Formula 3: Formula 3 in, is the concentration of radionuclides released into the environment during the current period, Radionuclides for ventilation systems Filtration efficiency; In step S40, the total amount of radionuclides released into the environment during the entire accident period is calculated according to Formula 4: Equation 4 in, The radionuclides during the entire accident Total releases to the environment.

2. The source term analysis method for reactor loss of coolant accident according to claim 1, characterized in that: There are multiple independent compartments outside the containment. In step S10, the concentration of radionuclides in the containment during the transient process is calculated according to formula 5: Formula 5 in, is the radionuclide concentration in the containment during the transient process, For radionuclides The decay constant of For radionuclides The sedimentation factor, is the leakage rate from the containment to the kth compartment.

3. The source term analysis method for reactor loss of coolant accident according to claim 2, characterized in that: In step S20, the current radionuclide concentration in the cabin k is calculated according to formula 6: Formula 6 in, is the current radionuclide concentration in the kth cabin, is the radionuclide concentration in the kth cabin at the previous moment, is the concentration of radionuclides in the containment at the previous moment, is the ventilation rate of the kth cabin.

4. The source term analysis method for reactor loss of coolant accident according to claim 3, characterized in that: In step S30, the concentration of radionuclides released to the environment from the kth cabin in the current period is calculated according to Formula 7: Formula 7 in, is the concentration of radionuclides released into the environment from the kth compartment in the current period, The ventilation system of the kth compartment is Filtration efficiency.

5. The method for source term analysis of reactor loss of coolant accident according to claim 4, characterized in that: In step S40, the total amount of radionuclides released into the environment during the entire accident period is calculated according to formula 8 and formula 9: Formula 8 Formula 9 in, is the radionuclide in the kth compartment during the entire accident The total amount released to the environment, The radionuclides during the entire accident Total releases to the environment.

6. A source term analysis system for a reactor loss of coolant accident, comprising a processor and a memory storing a computer program, characterized in that: The processor implements the steps of the source term analysis method for a reactor loss of coolant accident as described in any one of claims 1 to 5 when executing the computer program.

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