Method for calculating the frequency of administrative shutdowns and reactor stoppages in nuclear power plants using fault tree analysis
By combining fault tree models with reliability data to calculate the frequency of administrative shutdowns and reactor stoppages at nuclear power plants, the problem of estimation uncertainty in existing technologies has been solved, and more accurate prediction of shutdown and reactor stoppage frequencies has been achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI NUCLEAR ENGINEERING RESEARCH & DESIGN INSTITUTE CO LTD
- Filing Date
- 2023-10-30
- Publication Date
- 2026-06-30
AI Technical Summary
In existing technologies, the estimation of the frequency of administrative shutdowns and reactor shutdowns of nuclear power plants based on power plant operating experience has significant uncertainties, leading to inconsistent calculation results.
Using the fault tree approach, combined with reliability data and equipment failure mode analysis, a fault tree model is established to calculate the frequency of administrative shutdowns and reactor stoppages at nuclear power plants.
It provides a more scientific calculation method that is more in line with the actual situation of power plants, reduces human judgment errors, and improves the accuracy of calculation results.
Smart Images
Figure CN117390876B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of nuclear power plant shutdown frequency calculation, and in particular to a method for calculating the administrative shutdown frequency of nuclear power plants using fault tree analysis. Background Technology
[0002] In existing technologies, the average annual outage frequency of nuclear power plants is one of the important indicators for measuring the economics of nuclear power plants. In addition to automatic shutdowns triggered by fault signals of critical power generation equipment, another reason for nuclear power plant shutdowns is administrative or manual shutdowns due to failures of safety-related equipment or power generation auxiliary equipment, or failure to meet regulatory or user requirements.
[0003] In the Operating Limitations (LCO) or user requirements documents in the technical specifications, when certain critical systems or equipment fail, the power plant is required to restore them within a specified time; otherwise, the power plant will enter a post-shutdown phase.
[0004] Therefore, when estimating the frequency of administrative shutdowns, in addition to considering the reliability of the equipment, the possibility of power plant recovery must also be taken into account, which increases the difficulty of estimation.
[0005] Currently, the frequency of administrative shutdowns is generally estimated based on the operating experience of power plants, but this method is subject to significant uncertainty. For example, previous methods relied on the experience of engineers and technicians to determine the frequency of administrative shutdowns. Such results are closely related to the experience of personnel, and even within the same nuclear power plant, different personnel may give different judgments, resulting in considerable uncertainty.
[0006] In view of this, the applicant of this invention has designed a method for calculating the frequency of administrative shutdowns and reactor shutdowns in nuclear power plants using fault trees, in order to overcome the above-mentioned technical problems. Summary of the Invention
[0007] The technical problem to be solved by this invention is to overcome the shortcomings of the existing technology that estimates based on power plant operating experience, which has a large degree of uncertainty. This invention provides a method for calculating the frequency of administrative shutdowns and reactor shutdowns in nuclear power plants using fault trees.
[0008] The present invention solves the above-mentioned technical problems through the following technical solution:
[0009] A method for calculating the frequency of administrative shutdowns and reactor stoppages in nuclear power plants using fault tree analysis, characterized in that the method includes the following steps:
[0010] S1. Screening and equipment failure impact analysis based on administrative requirements: Based on operating constraints or power plant requirements, identify potential administrative shutdowns or reactor stoppages that may occur in the system, and conduct failure mode and impact analysis on the system.
[0011] S2. Reliability Data Collection: Collect reliability data for the equipment analyzed in step S1.
[0012] S3. Establish a fault tree model: Improve the PSA fault tree modeling method to make it applicable to the calculation of administrative shutdown and reactor stop frequency;
[0013] S4. Quantitative calculation: Based on the reliability data collected in step S2 and the formula given in step S3, calculate the equipment failure probability and failure frequency.
[0014] According to an embodiment of the present invention, step S1 includes:
[0015] S 11 Based on the nuclear power plant's technical specifications or other power plant requirements documents, identify potential administrative shutdowns that the system might experience.
[0016] S 12 Draw the system's reliability functional block diagram;
[0017] S 13 Failure mode and effect analysis was conducted on the relevant equipment to identify the equipment and failure modes that could trigger the above-mentioned administrative shutdown conditions, and various possible logical combinations were sorted out to form an administrative shutdown analysis list.
[0018] According to one embodiment of the present invention, the types of reliability data in step S2 include random equipment failure data, common cause equipment failure data, equipment operating time or number of operations, test and maintenance unavailability data, and repair time data.
[0019] According to an embodiment of the present invention, step S2 includes the following steps:
[0020] S 21 First, the data acquisition equipment is divided into several equipment categories. Each equipment category is a set of equipment with similar process performance, functions and operating conditions.
[0021] S 22 According to the steps S 13 The failure mode list is used to collect data on failure modes, and the reliability data comes from the operating records of specific nuclear power plants;
[0022] S 23 Calculate the reliability parameters for each type of equipment.
[0023] According to an embodiment of the present invention, step S 23 The reliability parameters that need to be calculated and the calculation methods include:
[0024] Failure rate λ:
[0025] Probability of requirement failure Q:
[0026] Equipment repair rate μ:
[0027] Unavailability P TM :
[0028]
[0029] According to an embodiment of the present invention, step S 22 The sources of data collection include power plant defect notifications, status reports, work orders, real-time data acquisition systems, and operation logs.
[0030] According to an embodiment of the present invention, the improvement of the PSA fault tree modeling method in step S3 includes:
[0031] Administrative shutdowns and reactor stoppages are designated as the top event in the fault tree, and these top events are decomposed into various system failures. Based on the triggerable administrative shutdowns and reactor stoppages obtained in step S1, corresponding failure events are established. These events are then analyzed using the RBD diagram, system flowchart, and step S1. 13 The failure mode list is used to build a fault tree branch downwards until the failure of equipment in the administrative shutdown analysis list is modeled.
[0032] According to an embodiment of the present invention, the improvement of the PSA fault tree modeling method in step S3 further includes: taking equipment failures in the administrative shutdown and outage analysis list as basic events of the fault tree, and the basic events are divided into probabilistic events and frequency events.
[0033] According to one embodiment of the present invention, if a runtime failure occurs, the probabilistic event adopts an unrepairable task time model, and the calculation method is as follows:
[0034] Q(t) = 1 - e -λt
[0035] Where t is the time allowed by the power plant for the equipment to be repaired, and Q is the failure probability;
[0036] If a demand failure occurs, the probabilistic event adopts a probabilistic model, and the failure probability Q is usually a constant that does not change with time, taking the demand failure probability data in step S2.
[0037] The calculation method for the frequency events is as follows:
[0038] F(t) = (1 - Q(t))λt
[0039] Where Q(t) is the probability of equipment failure and λ is the equipment failure rate.
[0040] According to an embodiment of the present invention, the improvement of the PSA fault tree modeling method in step S3 further includes: modeling the probability that the system or equipment cannot be repaired at time t in the fault tree, and the calculation method is as follows:
[0041] P(t=e -μt
[0042] Where μ is the equipment repair rate and t is the allowable repair time.
[0043] The positive and progressive effects of this invention are as follows:
[0044] This invention utilizes a fault tree method to calculate the frequency of administrative shutdowns and reactor shutdowns in nuclear power plants. Based on the reliability and repair capabilities of the power plant's own equipment, it provides a more scientific calculation method that is more in line with the characteristics of the power plant itself and reduces the judgment errors of different personnel, making the calculation results more consistent with the actual situation of the power plant. Attached Figure Description
[0045] The above and other features, properties and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, in which the same reference numerals always denote the same features, wherein:
[0046] Figure 1 This is a schematic diagram of the reliability block diagram of the method for calculating the frequency of administrative shutdowns and reactor shutdowns in nuclear power plants using fault trees, taking the chemical and volume control system of a nuclear power plant as an example.
[0047] Figure 2 This is a schematic diagram of a nuclear power plant administrative shutdown fault tree model a, using the chemical and volume control system of a nuclear power plant as an example, in the method of calculating the frequency of administrative shutdowns of nuclear power plants using fault trees in this invention.
[0048] Figure 3 This is a schematic diagram of the fault tree model b for administrative shutdowns of nuclear power plants, using the chemical and volume control system of a nuclear power plant as an example, in the method for calculating the frequency of administrative shutdowns of nuclear power plants using fault trees in this invention. Detailed Implementation
[0049] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0050] Embodiments of the invention will now be described in detail with reference to the accompanying drawings. Preferred embodiments of the invention will now be described in detail, examples of which are shown in the drawings. Wherever possible, the same reference numerals will be used in all the drawings to denote the same or similar parts.
[0051] Furthermore, although the terminology used in this invention is selected from commonly known and used terms, some terms mentioned in this specification may have been selected by the applicant in his or her judgment, and their detailed meanings are explained in the relevant sections of the description herein.
[0052] Furthermore, the invention should be understood not only through the actual terminology used, but also through the meaning implied by each term.
[0053] This invention discloses a method for calculating the frequency of administrative shutdowns and reactor stoppages in nuclear power plants using fault tree analysis, comprising the following steps:
[0054] Step S1: Screening and analysis of equipment failure impacts based on administrative requirements.
[0055] Based on operating constraints or power plant requirements, identify potential administrative shutdowns or reactor stoppages that may occur with the system, and conduct a failure mode and effects analysis (FMEA) of the system.
[0056] like Figure 1 As shown, this can be done in conjunction with a reliability block diagram (RBD) to determine the list of functions and equipment that enter operational constraint conditions, as well as the allowable recovery time. A more detailed explanation can be provided using the chemical and volumetric control system (CVS) of a nuclear power plant as an example:
[0057] Step S1 preferably includes:
[0058] Step S 11 Based on the nuclear power plant's technical specifications or other plant requirements documents, identify potential administrative shutdowns that could result from the system (e.g., the nuclear power plant's chemical and volumetric control system, CVS):
[0059] I. Operating limitations of the technical specifications are shown in Table 1 below.
[0060] Table 1:
[0061]
[0062] II. Operating restrictions of the technical specifications are shown in Table 2 below.
[0063] Table 2:
[0064]
[0065] III. Power Plant Operation Requirements: Water Makeup for the Chemical and Volumetric Control System (CVS) of Nuclear Power Plants
[0066] When one CVS (chemical and volume control system) charging pump becomes unavailable, a conservative estimate is that two charging pumps should be restored to a usable state within 7 days; otherwise, power reduction or reactor shutdown should be implemented.
[0067] IV. Power Plant Operation Requirements: CVS filtration and purification in nuclear power plant chemical and volumetric control systems.
[0068] If the CVS filtration and purification functions are unavailable, it is advisable to restore the filtration and purification functions within 7 days; otherwise, the reactor should be shut down.
[0069] V. Power Plant Operation Requirements: CVS Hydrogen Injection
[0070] If the CVS hydrogen injection function fails, it is conservatively considered to restore the hydrogen injection function within 7 days; otherwise, the reactor should be shut down.
[0071] Step S 12 Draw a reliability functional block diagram of a system (e.g., a chemical and volumetric control system (CVS) for a nuclear power plant).
[0072] like Figure 1 As shown, the administrative requirements identified in the first step all pertain to CVS water replenishment equipment. The equipment performing the water replenishment function includes boric acid storage tank, boric acid storage tank circulation pump, CVS water replenishment pump A, CVS water replenishment pump B, and related pipes, instruments, and valves.
[0073] Step S 13 1. Conduct Failure Mode and Effects Analysis (FMEA) on the relevant equipment to identify the equipment and failure modes that could trigger the aforementioned administrative shutdown conditions, and to identify all possible logical combinations to form an administrative shutdown analysis list, as shown in Table 3 below. During the analysis process, information from the system specifications and flowcharts should be fully incorporated, and equipment failure modes should be fully integrated with those considered in Probabilistic Safety Assessment (PSA).
[0074] Table 3:
[0075]
[0076] Step S2, Reliability Data Collection
[0077] Reliability data is collected for the equipment analyzed in step S1. To enable model quantification, reliability data needs to be collected for the equipment analyzed in step one. The data source can be the power plant's own operational data, data from similar power plants, or general industry data for nuclear power plants.
[0078] Preferably, the types of reliability data in step S2 include random equipment failure data, common cause equipment failure data, equipment operating time or number of actions, test and maintenance unavailability data, and repair time data.
[0079] Step S2 includes the following steps:
[0080] Step S 21First, the data acquisition equipment is divided into several equipment categories. Each equipment category is a set of equipment with similar process performance, functions and operating conditions.
[0081] Step S 22 According to the steps S 13 The failure mode list (i.e., Table 3 above) is used to collect data on failure modes, and the reliability data comes from the operation records of specific nuclear power plants.
[0082] Data collection should be conducted according to the failure modes listed in Table 3, and reliability data should be obtained from specific nuclear power plant operation records whenever possible. Data sources include plant defect notifications, status reports, work orders, real-time data acquisition systems, and operation logs. If the nuclear power plant has deployed an equipment reliability database system, that system can be used for data collection.
[0083] Step S 23 Calculate the reliability parameters for each type of equipment.
[0084] Preferably, step S 23 The reliability parameters that need to be calculated and the calculation methods include:
[0085] Failure rate λ:
[0086]
[0087] Probability of requirement failure Q:
[0088]
[0089] Equipment repair rate μ:
[0090]
[0091] Unavailability P TM :
[0092]
[0093] In cases where reliability data is lacking for a specific nuclear power plant, the reliability data of the plant's PSA equipment or a general nuclear power database can be used as a reference, and then adjustments can be made in conjunction with the plant's operating data (using engineer's experience judgment or Bayesian updates).
[0094] Step S3: Establish a fault tree model
[0095] A fault tree is a visual representation of the Boolean logic relationships between faulty devices; a fault tree is essentially a logic diagram. It describes how the occurrence of a single event causes certain events to occur sequentially, with these events tightly linked together. The triggering logic of these events is represented by special symbols such as AND and OR gates.
[0096] Fault trees have been used in PSA in a relatively mature way. The technical solution of this application is to improve the PSA fault tree modeling method so that it can be applied to the calculation of administrative shutdown and outage frequency.
[0097] Preferably, the improvement to the PSA fault tree modeling method in step S3 includes:
[0098] I. Administrative shutdown or reactor stoppage as the top event of the fault tree (e.g.) Figure 2 As shown), the top event is decomposed into system failures; based on the triggerable administrative shutdowns and reactor stoppages obtained in step S1, corresponding failure events are established; based on the RBD diagram, system flowchart, and step S1... 13 The failure mode list is used to build a fault tree branch downwards until the failure of equipment in the administrative shutdown analysis list is modeled.
[0099] Specifically, the top event of a fault tree is located at the very top of the fault tree. It is generally an event or accident that causes serious consequences and is the final result of equipment failure. The top event is then decomposed downwards into the failures of individual systems.
[0100] Taking the CVS system (chemical and volumetric control system of a nuclear power plant) as an example, according to step S1, there are four types of administrative shutdowns that can be triggered by the CVS: isolation valve failure and failure to restore on time, makeup water failure and failure to restore on time, filtration and purification failure and failure to restore on time, and hydrogen injection failure and failure to restore on time. Therefore, these four failure events are established. Next, based on the CVS's RBD diagram, system flowchart, and step S1... 13 The list (as shown in Table 3) is used to build a fault tree branch downwards until the failure of the device in Table 3 is modeled.
[0101] II. The equipment failures in the administrative shutdown and outage analysis list are used as the basic events in the fault tree. The basic events are divided into probabilistic events and frequency events.
[0102] Probabilistic events: Probabilistic events represent the probability of equipment failure at time t.
[0103] If an operational failure occurs (such as a failure of the water supply pump, valve leakage, malfunction, etc.), the probabilistic event will be calculated using an unrepairable task-time model, as follows:
[0104] Q(t) = 1 - e -λt
[0105] Where t is the time allowed by the power plant for the equipment to be repaired, and Q is the failure probability; for the CVS system, it is 168 hours (7 days).
[0106] If a demand failure occurs (such as a water pump failure to start, a valve that cannot be opened / closed, etc.), the probabilistic event adopts a probabilistic model, and the failure probability Q is usually a constant that does not change with time, taking the demand failure probability data in step S2.
[0107] Frequency-based events: Frequency-based events represent the estimated number of times a fault will occur within time t.
[0108] The calculation method for the frequency events is as follows:
[0109] F(t) = (1 - Q(t))λt
[0110] Where Q(t) is the probability of equipment failure, and λ is the equipment failure rate. If we are concerned with the expected frequency of nuclear power plant outages over one year, t = 8760 hours.
[0111] III. The probability that a system or device cannot be repaired at time t is modeled in the fault tree and calculated as follows:
[0112] P(t=e -μt
[0113] Where μ is the equipment repair rate and t is the allowable repair time.
[0114] The task duration is one year, or 8760 hours. For probabilistic events, if the failure is an operational failure, an unrepairable task duration model is adopted, and the task duration is the repair time allowed by the LCO. If the failure is a requirement failure event, a requirement failure model is adopted.
[0115] Step S4: Quantitative Calculation
[0116] Based on the reliability data collected in step S2 and the formula given in step S3, the probability of equipment failure and the frequency of failure are calculated.
[0117] Fault tree model quantification is typically performed using software, incorporating Boolean algebra rules to transform the logical model into combinations of equipment failures that cause administrative shutdowns. These combinations of equipment failures are called minimal cut sets. By assigning a corresponding failure frequency / probability to each device in each cut set, the product of the failure frequencies / probabilities of all devices in each cut set is the frequency of occurrence of that cut set. The sum of the frequencies of all cut sets corresponding to a given top event determines the frequency of administrative shutdowns caused by that top event, i.e., the annual average shutdown frequency caused by the system.
[0118] Typically, fault tree software can not only obtain cut sets using Boolean algebra rules, but also obtain the frequency / probability of the top event based on the frequency / probability of device failures, as well as sort the list of cut sets that lead to the top event.
[0119] Based on the above method description, this invention proposes a method for calculating the frequency of administrative shutdowns and reactor shutdowns in nuclear power plants using fault trees. A fault tree is a logical causal relationship diagram that shows how equipment failures or combinations of equipment failures will lead to system failures.
[0120] The structural elements of a system fault tree are equipment failure events and logic gates: failure events describe the equipment failure state; logic gates connect the events and represent the logical relationships between them. By analyzing the equipment, environment, and human factors that may cause system failure, a fault tree is built to determine the combinations of equipment failures that lead to system failure and their probability of occurrence.
[0121] In summary, the method for calculating the frequency of administrative shutdowns and reactor shutdowns in nuclear power plants using fault tree analysis, based on the plant's own equipment reliability and repair capabilities, provides a more scientific calculation method that better reflects the characteristics of the power plant and reduces the judgment errors of different personnel, making the calculation results more consistent with the actual situation of the power plant.
[0122] For those skilled in the art, the above disclosure is merely illustrative and does not constitute a limitation of this application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are suggested in this application and therefore remain within the spirit and scope of the exemplary embodiments of this application.
[0123] Furthermore, this application uses specific terms to describe embodiments of the application. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic related to at least one embodiment of the application. Therefore, it should be emphasized and noted that "an embodiment," "one embodiment," or "an alternative embodiment" mentioned twice or more in different locations in this specification do not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.
[0124] Similarly, it should be noted that, in order to simplify the description of the embodiments disclosed in this application and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of the embodiments of this application sometimes combines multiple features into a single embodiment, drawing, or description thereof. However, this disclosure method does not imply that the subject matter of this application requires more features than those mentioned in the claims. In fact, the embodiments have fewer features than all the features of the single embodiments disclosed above.
[0125] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.
Claims
1. A method for calculating the frequency of administrative shutdowns and reactor stoppages in nuclear power plants using fault tree analysis, characterized in that, The method for calculating the frequency of administrative shutdowns and reactor stoppages at nuclear power plants using fault trees includes the following steps: S1. Screening and equipment failure impact analysis based on administrative requirements: Based on operating constraints or power plant requirements, identify potential administrative shutdowns or reactor stoppages that may occur in the system, and conduct failure mode and impact analysis on the system. S2. Reliability Data Collection: Collect reliability data for the equipment analyzed in step S1; S3. Establish a fault tree model: Improve the PSA fault tree modeling method to make it applicable to the calculation of administrative shutdown and reactor stop frequency; S4. Quantitative calculation: Combining the reliability data collected in step S2 and the formula given in step S3, calculate the equipment failure probability and failure frequency. The improvements made to the PSA fault tree modeling method in step S3 include: Administrative shutdown and refueling stoppage are taken as the top event of the fault tree, and the top event is decomposed into various system failures. Based on the triggerable administrative shutdown and refueling stoppages obtained in step S1, corresponding failure events are established. Based on the RBD diagram, system flowchart, and failure mode list that can trigger administrative shutdown and refueling stoppage conditions, fault tree branches are established downwards until the equipment failure in the administrative shutdown and refueling stoppage analysis list is modeled. The improvement to the PSA fault tree modeling method in step S3 also includes: taking equipment failures in the administrative shutdown and outage analysis list as the basic events of the fault tree, and the basic events are divided into probabilistic events and frequency events; If a runtime failure occurs, the probabilistic event will be calculated using an unrecoverable task time model, as follows: Q(t) = 1 - e -λt Where t is the time allowed by the power plant for the equipment to be repaired, and Q is the failure probability; If a demand failure occurs, the probabilistic event adopts a probabilistic model, and the failure probability Q is usually a constant that does not change with time. The equipment demand failure probability data in the reliability data collected in step S2 is taken. The method for calculating frequency events is as follows: F(t) = (1 - Q(t))λt Where Q(t) is the probability of equipment failure, λ is the equipment failure rate, and F(t) represents the frequency of occurrence of the frequency event; In the fault tree, the probability that a system or device cannot be repaired at time t is modeled and calculated as follows: P(t) = e -μt Where μ is the equipment repair rate and t is the allowable repair time.
2. The method for calculating the frequency of administrative shutdowns and reactor stoppages at nuclear power plants using fault tree analysis as described in claim 1, characterized in that, Step S1 includes: S 11 , Administrative shutdowns that can result from the system combing through the technical specifications of the nuclear power plant or other plant requirement documents; S 12 , a reliability functional block diagram of the mapping system; S 13 , Conduct failure mode and effect analysis on related equipment, identify the list of equipment and failure modes that can trigger the administrative shutdown and shutdown conditions described above, and sort out various possible logical combination relationships to form an administrative shutdown analysis list.
3. The method for calculating the frequency of administrative shutdowns and reactor stoppages in nuclear power plants using fault tree analysis as described in claim 1, characterized in that... The types of reliability data in step S2 include random equipment failure data, common cause equipment failure data, equipment operating time or number of actions, test and maintenance unavailability data, and repair time data.
4. The method for calculating the frequency of administrative shutdowns and reactor stoppages at nuclear power plants using fault tree analysis as described in claim 2, characterized in that... Step S2 includes the following steps: S 21 The acquisition device is first divided into several device classes, and a device class is a set of devices with similar process performance, functions, and operating conditions. S 22 , in accordance with the steps S 13 in the failure mode list, data collection is carried out for the failure mode, and the reliability data comes from the operation records of a specific nuclear power plant; S 23 , calculating reliability parameters for each device class.
5. The method for calculating the frequency of administrative shutdowns and reactor stoppages at nuclear power plants using fault tree analysis as described in claim 4, characterized in that... The step S 23 The reliability parameters and calculation methods that need to be calculated include: Equipment failure rate λ: Probability of requirement failure Q: Equipment repair rate μ: Unavailability P TM :
6. The method for calculating the frequency of administrative shutdowns and reactor stoppages at nuclear power plants using fault tree analysis as described in claim 4, characterized in that... The step S 22 The sources of data collection include power plant defect notifications, status reports, work orders, real-time data acquisition systems, and operation logs.