Method for determining probability of actually eliminating melting of reactor core

Abstract

The embodiment of the invention provides a method for determining the probability of actually eliminating reactor core melting, and relates to the field of nuclear power plant safety. The problem that the requirement for actually eliminating reactor core melting is not clear enough is solved. The method for determining the probability of actually eliminating reactor core melting comprises the steps that the reactor core melting frequency of the nuclear power plant is controlled to be smaller than or equal to 1E-8 / reactor year, under the condition that the reactor core melting frequency of the nuclear power plant is smaller than or equal to 1E-8 / reactor year, the nuclear power plant has actually eliminated reactor core melting, and the reactor core melting risk of the nuclear power plant can be ignored; therefore, the problem that the requirement for actually eliminating reactor core melting is not clear enough is solved.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power plant safety, and in particular to a method for determining the probability of actually eliminating core melting. Background Art

[0002] People pay great attention to the safety of nuclear power plants, and continuously improve the safety of nuclear power plants through improving design and strengthening analysis, and have formed a method of quantitatively evaluating the risks of nuclear power plants represented by probabilistic safety assessment (PSA). In the PSA method, the core melting frequency or core damage frequency is an important indicator, which is widely used by the International Atomic Energy Agency (IAEA) and countries around the world to quantify the risks of nuclear power plants.

[0003] From the 1990s to the 2010s, along with the research on nuclear power safety issues and the development of third-generation nuclear power technology, the IAEA and European countries proposed the concept and requirement of "designing to actually eliminate the release of large amounts of radioactive materials" in response to large amounts of radioactive releases, that is, to eliminate serious accident sequences that may produce large amounts of radioactive materials through design means and mitigate radioactive consequences. With the continuous improvement and optimization of the design and operation of nuclear power plants, the frequency of core melts has continued to decline, making it possible to "design to actually eliminate core melts." However, the requirements that need to be met for "designing to actually eliminate core melts" are still unclear. Summary of the invention

[0004] A brief summary of one or more aspects is given below to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceived aspects, and is neither intended to identify the key or critical elements of all aspects nor to define the scope of any or all aspects. Its only purpose is to give some concepts of one or more aspects in a simplified form as a prelude to a more detailed description that will be given later.

[0005] Objectives of the present invention include, for example, providing a method for determining the probability of actually eliminating core melting, which can improve the problem that the requirements for achieving the actual elimination of core melting are not clear enough.

[0006] The embodiments of the present invention can be implemented as follows: An embodiment of the present invention provides a method for determining the probability of actually eliminating core melting, comprising: Control the core melt frequency of nuclear power plants to less than or equal to 1E-8 / reactor-year.

[0007] In addition, the method for determining the probability of actually eliminating core melting provided by the embodiment of the present invention may also have the following additional technical features: Optionally, the step of controlling the core melting frequency of the nuclear power plant to be less than or equal to 1E-8 / reactor-year comprises: Control the core melt frequency of nuclear power plants to be less than or equal to the mass extinction frequency.

[0008] Optionally, the step of controlling the core melting frequency of the nuclear power plant to be less than or equal to 1E-8 / reactor-year comprises: Control the frequency of core melts in nuclear power plants to a level lower than the probability of risk that can be ignored by the public.

[0009] Optionally, the step of controlling the core melting frequency of the nuclear power plant to be less than or equal to 1E-8 / reactor-year comprises: Controlling the frequency of core melts in nuclear power plants is less than the frequency of actually eliminating the release of large amounts of radioactive material.

[0010] The beneficial effects of the method for determining the probability of actually eliminating core melting according to the embodiment of the present invention include, for example: An embodiment of the present invention provides a method for determining the probability of actually eliminating core melting, comprising: controlling the core melting frequency of a nuclear power plant to be less than or equal to 1E-8 / reactor-year.

[0011] By comparing the risks caused by nuclear power plants with natural risks and social risks, a technical route for determining a sufficiently low relative risk value is proposed. That is, starting from the essence of nuclear safety, the frequency of mass extinction events and the acceptable risk level for the public are studied and analyzed. On this basis, combined with the probability requirement of "actually eliminating the release of large amounts of radioactive materials" for nuclear power plants, a cutoff probability value for the "actual elimination of core melt" evaluation criterion is proposed. When the frequency of core melt in a nuclear power plant is less than or equal to 1E-8 / reactor-year, it is considered that core melt has been actually eliminated, thus improving the problem of unclear requirements for achieving the actual elimination of core melt. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above features and advantages of the present invention can be better understood after reading the detailed description of the embodiments of the present disclosure in conjunction with the following drawings. In the drawings, the components are not necessarily drawn to scale, and components with similar related properties or features may have the same or similar reference numerals.

[0013] Figure 1 The calculation basis of the mass extinction frequency in the method for determining the probability of actually eliminating core melt provided by the embodiment of the present invention; Figure 2 A flow chart of a method for determining the probability of actually eliminating core melt provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0014] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Note that the aspects described below in conjunction with the accompanying drawings and specific embodiments are only exemplary and should not be construed as limiting the scope of protection of the present invention in any way.

[0015] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", "vertical" and the like appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, or is the orientation or position relationship in which the product of the invention is usually placed when used, rather than indicating or implying that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0016] At the same time, it should be noted that the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0017] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified or limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, an integral connection, or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or the internal communication of two components, etc. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0018] The essence of the safety goal of a nuclear power plant is to compare the risks caused by the nuclear power plant with other social risks. As long as the nuclear power plant does not significantly increase social risks, it means that the nuclear power plant is safe enough. The purpose of determining the probability of "actually eliminating core melt" is that when the frequency of core melt in a nuclear power plant is lower than this frequency, it can be considered that public health and environmental risks will not be affected.

[0019] At present, there is no research on the actual elimination of core melting in public data at home and abroad, let alone the actual elimination of core melting probability. This embodiment determines the probability of "actual elimination of core melting" of nuclear power plants through the analysis of the frequency of biological extinction events on Earth and the study of acceptable risk levels for the public, combined with the probability of "actual elimination of large-scale radioactive material release" of nuclear power plants. Its physical meaning means that if the core melting frequency of a nuclear power plant is as low as the frequency of biological extinction events on Earth or is two orders of magnitude or more lower than the frequency of acceptable risk levels for the public, it can be considered that the nuclear power plant has achieved the actual elimination of core melting, that is, the core melting risk of the nuclear power plant can be ignored for the entire human society.

[0020] Combine the following Figure 1 and Figure 2 The method for determining the probability of actually eliminating core melting provided by this embodiment is described in detail.

[0021] Please refer to Figure 1 and Figure 2The embodiment of the present invention provides a method for determining the probability of actually eliminating core melting, including: controlling the core melting frequency of a nuclear power plant to be less than or equal to 1E-8 / reactor year. When the core melting frequency is less than or equal to 1E-8 / reactor year, the core melting can be actually eliminated.

[0022] It should be noted that the "core melt frequency of nuclear power plants" is one of the important indicators for evaluating the safety of nuclear power plants. Core melting, also known as core melting, refers to the excessive rise in temperature of the nuclear reactor, causing the fuel rods to melt and break. It is the most serious accident that may occur in a nuclear power plant.

[0023] "1E-8 / reactor-year" is a numerical value indicating frequency. "E-8" is a way of expressing scientific notation, which is equivalent to 10 to the negative 8th power, that is, 0.00000001. " / reactor-year" means that this frequency is a statistic for each reactor's annual operation.

[0024] Specifically, during the implementation process, based on the design and operation of the nuclear power plant, we carried out power plant operating status analysis, initiating event analysis, event tree analysis, fault tree analysis, personnel reliability analysis, data analysis, common cause analysis, etc., established a probabilistic safety assessment model, quantified the core damage frequency, discovered deficiencies in the design or operation, modeled the design improvements into the probabilistic safety assessment model, and re-quantified them, thereby further reducing the core damage frequency and improving the safety of the nuclear power plant.

[0025] Reference Figure 1 In this embodiment, the step of controlling the core melting frequency of the nuclear power plant to be less than or equal to 1E-8 / reactor-year includes: controlling the core melting frequency of the nuclear power plant to be less than or equal to the mass extinction frequency.

[0026] When a large-scale destructive natural disaster occurs on Earth that causes the extinction of most species, humans will have already perished, and even if a nuclear power plant core melts, it will not pose a threat to human casualties. If the frequency of nuclear power plant core melts is equivalent to the frequency of species extinction, then from the perspective of probability theory, it can be considered that core melts have been practically eliminated.

[0027] According to the research of Nanjing Institute of Geology and Paleontology of Chinese Academy of Sciences, there have been five mass extinctions on Earth in the past 500 million years, namely: 1) At the end of the Ordovician period about 443 million years ago (Ma), 85% of species were extinct; 2) At the end of the Devonian period about 372 Ma, marine life suffered a catastrophe; 3) At the end of the Permian period about 252 Ma, 90% of organisms were extinct; 4) At the end of the Triassic period about 201 Ma, reptiles were hit hard; 5) At the end of the Cretaceous period about 66 Ma, more than 70% of species including dinosaurs, ammonites, belemnites, planktonic foraminifera, most birds and primitive mammals became extinct. The common characteristics of the "five major biological extinctions" are that more than 2 / 3 of species disappeared, the time was short (within a million years), global, affected most categories, severely damaged community structure, and changed the biogeographic pattern.

[0028] Based on the above data, the frequency of mass extinction is calculated to be about 5 times / 500 million years = 1E-8 / year. Therefore, from the perspective of mass extinction, if the frequency of nuclear power plant core melt is equal to or lower than this frequency, core melt can be actually eliminated.

[0029] In this embodiment, the step of controlling the core melting frequency of the nuclear power plant to be less than or equal to 1E-8 / reactor-year includes: controlling the core melting frequency of the nuclear power plant to be less than the risk probability that can be ignored by the public.

[0030] In order to quantitatively analyze the acceptable risk level for the public, foreign governments and institutions have formulated various standards for their own maximum acceptable risk level (MARL) and applied them to risk management. Studies have found that 1E-6 is the risk level imposed on humans by the natural environment without any human control. This is a risk that humans can accept without risk control. However, due to different types of risks, even at the same risk level, the public's acceptability varies greatly. Foreign scholars believe that in terms of carcinogenic environmental risks, the risk level of 1E-6 is acceptable.

[0031] The report of the United Nations Energy Agency (UNEP) pointed out that for industrial activities, 1E-3 is an unacceptable risk level for the public, but the public can accept other activities with the same risk level (such as motorcycles). Foreign institutions and scholars believe that "the basis for determining the maximum acceptable risk level and the negligible risk level is to compare with the common risk level, compare with the lowest mortality rate, or calculate from the shortening of the average expected life." Therefore, it can be concluded that the MARL is 1E-6~1E-5, and the negligible risk level is 1E-8~1E-7.

[0032] The U.S. Environmental Protection Agency (EPA) has included carcinogenic risk levels of 1E-6 to 1E-4 in the risk management scope and considers 1E-6 to be the inherent carcinogenic risk level for soil, air and water, that is, the corresponding MARL is 1E-6 / year.

[0033] Based on the above research, the public can ignore the risk level below the maximum acceptable risk level, which is generally 1E-8 to 1E-7 per year. If the core melt frequency of a nuclear power plant is equivalent to or lower than this frequency, it can be considered that core melts have been practically eliminated.

[0034] In this embodiment, the step of controlling the core melting frequency of the nuclear power plant to be less than or equal to 1E-8 / reactor-year includes: controlling the core melting frequency of the nuclear power plant to be less than the actual frequency of eliminating the release of a large amount of radioactive substances.

[0035] IAEA-TECDOC-1791 (considerations on the application of the IAEA safety requirements for the design of nuclear power plants) provides guidance on the specific implementation of "practically eliminating large releases of radioactive materials", and believes that for nuclear power plants with new designs, the frequency of early or large releases of radioactive materials is expected to be less than 1E-6 / reactor year, and these conditions are extremely unlikely to occur, which can meet the goal of "practically eliminating large releases of radioactive materials". Therefore, if the core melt frequency is less than 1E-6 / reactor year, core melt can be practically eliminated.

[0036] According to a method for determining the actual probability of eliminating core melting provided by this embodiment, the working principle of the method for determining the actual probability of eliminating core melting includes: This embodiment proposes the concept of "practically eliminating core melts". By conducting research from the perspectives of biology, sociology and nuclear energy science, and comprehensively considering the frequency of mass extinctions, the level of risk that the public can ignore, and the frequency requirement of "practically eliminating the release of large amounts of radioactive substances" in nuclear power plants, a technical method for determining the cutoff frequency value that meets the requirement of "practically eliminating core melts" is given, which is conducive to verifying the high safety design level of nuclear power plants and ensuring public and environmental safety.

[0037] Based on the frequency of mass extinction of 1E-8 / year, the public negligible risk level of 1E-8 to 1E-7 / year, and the frequency of "actual elimination of large-scale radioactive material releases" lower than 1E-6 / reactor-year, the lowest frequency value is selected as the probability of actually eliminating core melts. That is, when the core melt frequency is less than or equal to 1E-8 / reactor-year, it is considered that the core melt has been actually eliminated.

[0038] The method for determining the probability of actually eliminating core melting provided by this embodiment has at least the following advantages: A method for determining the probability of actually eliminating core melts includes: controlling the core melt frequency of a nuclear power plant to be less than or equal to 1E-8 / reactor-year. When the core melt frequency of a nuclear power plant is less than or equal to 1E-8 / reactor-year, the nuclear power plant has achieved the actual elimination of core melts, that is, the core melt risk of the nuclear power plant can be ignored for the entire human society, which can improve the problem of unclear requirements for achieving the actual elimination of core melts.

[0039] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technology in the field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for determining the probability of actually eliminating a core melt, characterized in that: include: Control the core melt frequency of nuclear power plants to less than or equal to 1E-8 / reactor-year.

2. The method for determining the probability of actually eliminating core melting according to claim 1, characterized in that: The step of controlling the core melting frequency of the nuclear power plant to be less than or equal to 1E-8 / reactor year comprises: Control the core melt frequency of nuclear power plants to be less than or equal to the mass extinction frequency.

3. The method for determining the probability of actually eliminating core melting according to claim 2, characterized in that: The step of controlling the core melting frequency of the nuclear power plant to be less than or equal to 1E-8 / reactor year comprises: Control the frequency of core melts in nuclear power plants to a level lower than the probability of risk that can be ignored by the public.

4. The method for determining the probability of actually eliminating core melting according to claim 3, characterized in that: The step of controlling the core melting frequency of the nuclear power plant to be less than or equal to 1E-8 / reactor year comprises: Controlling the frequency of core melts in nuclear power plants is less than the frequency of actually eliminating the release of large amounts of radioactive material.

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