LOPA protective layer risk assessment method for nuclear fuel element manufacturing facility

Abstract

The invention relates to an LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility. The method comprises the following steps: S1, constructing a risk matrix; s2, collecting data of nuclear fuel element manufacturing facilities; s3, determining nodes according to the collected data, performing HAZOP analysis on each node, identifying potential deviation and causes of deviation generation, using a risk matrix to evaluate the nodes generating deviation, and screening out dangerous scenes; s4, identifying the independent protection layer of the dangerous scene, carrying out LOPA analysis, and calculating the residual risk and grade of an accident after the independent protection layer is reduced; and S5, aiming at the residual risk and the grade of the accident, putting forward safety countermeasures until the residual risk of the accident is reduced to the lowest feasible level. According to the risk assessment method, the industrial accident risk and the nuclear accident risk of the nuclear fuel element manufacturing facility can be systematically identified, the accident risk can be semi-quantitatively judged, feasible measures for reducing the accident risk are put forward, and safe operation of the facility is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear fuel cycle safety protection, and particularly relates to a LOPA protective layer risk assessment method for nuclear fuel element manufacturing facilities. Background Art

[0002] The manufacture of nuclear fuel elements is a process of converting UF 6 gas into UO 2 powder, and then processing the UO 2 powder into usable nuclear fuel elements. During the manufacturing process, in addition to involving conventional hazardous chemicals such as H 2 , HF, NH 3 , HNO 3 , etc., it also involves uranium-containing radioactive materials such as UF 6 , UO 2 , UO 2 F 2 . The accidents / events considered during the operation of nuclear fuel element manufacturing facilities mainly include nuclear criticality accidents, nuclear accidents such as UF 6 gas leakage accidents, and industrial accidents such as converter hydrogen explosion, sintering furnace hydrogen explosion, organic solvent fire, and hydrofluoric acid leakage accidents.

[0003] In China, it is clearly stated in the "Classification Principles and Basic Safety Requirements for Civil Nuclear Fuel Cycle Facilities" that all reasonably practicable measures should be taken to prevent accidents from occurring, and to mitigate their radiation consequences and chemical hazard consequences in the event of an accident; for all possible accidents considered in the design, including those with a very low probability, it is necessary to ensure with a high degree of confidence that the radiation consequences and chemical hazard consequences are as small as possible and below the specified limits, and to ensure that the probability of an accident with serious radiation consequences is extremely low.

[0004] In the current risk assessment of nuclear fuel element manufacturing facilities, the accidents / events considered mainly rely on operating experience, which may miss some accident scenarios. And radioactive material leakage accidents and nuclear criticality accidents occur under a series of abnormal conditions. Therefore, it is very important to construct a systematic risk assessment method for nuclear fuel element manufacturing facilities.

[0005] Currently, the LOPA protective layer analysis is based on qualitative risk assessment. It further analyzes the protection measures for unacceptable risks, uses a reasonable, objective, risk-based method to analyze the effectiveness of each protection measure, and then compares the accident risk under the combined action of all protective layers with the risk tolerance standard to provide a reasonable, semi-quantitative, risk-based assessment result, providing a decision-making basis for formulating preventive measures in advance. However, this method is usually used for safety analysis in the traditional chemical industry and is difficult to apply in the nuclear facility field.

[0006] When conducting LOPA analysis in the traditional chemical industry, attention is usually paid to the casualties and property losses caused by accidents. Compared with the traditional chemical industry, nuclear fuel element manufacturing facilities pay more attention to radioactive material leakage accidents and nuclear criticality accidents. Although the probability of such accidents occurring is extremely low and they will not cause major casualties, the environmental and reputational impacts are extremely serious. Therefore, for nuclear fuel element manufacturing facilities, it is necessary to classify the severity of nuclear accidents / events, establish an exclusive risk matrix and the acceptable level of risk. In addition, when identifying independent protection layers in the traditional chemical industry, management measures such as operating procedures and personnel training are usually not considered. Given the characteristics of nuclear materials, in addition to geometric safety control for some equipment when controlling nuclear criticality accidents in nuclear fuel element manufacturing facilities, quality control, concentration control and moderation control are generally adopted. Therefore, for nuclear fuel element manufacturing facilities, management measures have also become essential and feasible and effective protection measures. When conducting LOPA analysis of nuclear fuel element manufacturing facilities, management measures need to be used as independent protection layers to reduce the residual risk of accidents.

[0007] Therefore, there is an urgent need for a risk assessment method applicable to nuclear fuel element manufacturing facilities. Summary of the Invention

[0008] The present invention discloses a LOPA protection layer risk assessment method for nuclear fuel element manufacturing facilities, aiming to solve the technical problems existing in the prior art.

[0009] The present invention adopts the following technical solutions:

[0010] The present invention provides a LOPA protection layer risk assessment method for nuclear fuel element manufacturing facilities, including the following steps:

[0011] S1: Construct a risk matrix according to risk factors, risk severity and risk impact;

[0012] S2: Collect data of nuclear fuel element manufacturing facilities;

[0013] S3: Determine nodes according to the collected data, conduct HAZOP analysis on each node, identify potential deviations and the causes of deviations, and use the risk matrix to evaluate the nodes with deviations to screen out dangerous scenarios;

[0014] S4: Identify the independent protection layers of dangerous scenarios, conduct LOPA analysis, and calculate the residual risk and level of accidents after reduction by the independent protection layers;

[0015] S5: Put forward safety countermeasures for the residual risk and level of accidents until the residual risk of accidents is reduced to the lowest feasible level.

[0016] Preferably, in step S1, the risk factors include the impacts on the health and safety of staff, property losses, and radioactive accident impacts; the risk severity is classified into 5 levels of A, B, C, D, and E according to the grade, and the risk impact is classified into 7 levels of 1, 2, 3, 4, 5, 6, and 7 in ascending order of the likelihood of the accident occurring.

[0017] Preferably, in step S2, the collected data includes the geometric parameters, process parameters, material parameters, system process instrument flowcharts, operating procedures, engineering change records, and historical accident event statistical analysis data of the process equipment.

[0018] Preferably, in step S3, it specifically includes the following steps:

[0019] S31: Divide nodes for each equipment, process, and subsystem to determine the nodes;

[0020] S32: Use HAZOP analysis to determine keywords, process parameters, normal operating conditions, and guiding words for each node, and then determine the resulting deviations;

[0021] S33: For the nodes with safety risks, analyze all the reasons for the deviations, confirm the initial events, and determine the frequency of the events occurring;

[0022] S34: Analyze the consequences caused after the deviations occur in each node, and conduct a risk assessment on the consequences according to the risk matrix, evaluating the severity of the consequences, the likelihood of occurrence, and the risk level;

[0023] S35: Classify the risks of the dangerous scenarios caused by each deviation.

[0024] Preferably, in step S33, when analyzing the reasons for the deviations, the impacts of external events should also be considered. The external events include extreme weather, earthquakes, and external human events; in step S34, when conducting a risk assessment on the consequences, the environmental and social impacts caused by radioactive substances should also be considered.

[0025] Preferably, in step S35, according to the risk matrix and the risk evaluation index in the risk matrix, the risks are divided into low risks, general risks, relatively large risks, and major risks. Relatively large risks and major risks are the dangerous scenarios.

[0026] Preferably, in step S4, for the relatively large risk scenarios and major risk scenarios identified by HAZOP analysis, identify the independent protection layers of the dangerous scenarios, determine the failure probability according to the correlation of the initial events, whether the independent protection layers are shared, the consequence frequency caused by multiple initial events, and fully consider the enabling conditions and the impacts of correction factors, and calculate the remaining risk and level of the accident after the independent protection layer is reduced.

[0027] Preferably, in step S4, for a nuclear criticality accident, the nuclear fuel element manufacturing facility adopts five layers of defense-in-depth measures including conservative design, high-quality construction / commissioning and operation, setting up protection barriers, system monitoring and alarm and interlock, fail-safe design, radioactive material containment, and on-site and off-site emergency response. The independent protection layers include geometric safety, geometric control, concentration control and moderation control, quality control, and spacing control.

[0028] Preferably, in step S4, for a radioactive material leakage accident, the independent protection layers include container pressure resistance design, DCS control system, conductivity meter and HF detection and alarm, accident ventilation filtration and purification system, operating procedures, and personnel training.

[0029] Preferably, in step S5, the residual risk level of the accident should be reduced to a low risk level. For a radioactive material leakage or nuclear criticality accident, the possibility of the accident occurring should be ensured to be reduced to 10 -6 and below. If the independent protection layers do not meet the requirements, reasonable and feasible independent protection layers should be added to further reduce the risk level.

[0030] The technical solution adopted by the present invention can achieve the following beneficial effects:

[0031] (1) The present invention combines various methods such as risk matrix, HAZOP analysis (Hazard and Operability Study), and LOPA analysis (Layer of Protection Analysis) to form a comprehensive risk assessment method. This method not only considers the possibility and consequence severity of the accident but also particularly focuses on the special risks of radioactive material leakage and nuclear criticality accidents.

[0032] (2) The present invention introduces the concept of independent protection layer (IPL), incorporates soft measures such as management and personnel training as independent protection layers into the risk assessment, reflects the importance of nuclear safety culture, and this multi-level protection design can effectively reduce the risk of accident occurrence.

[0033] (3) The present invention realizes the semi-quantitative assessment of risk by constructing a risk matrix and combining HAZOP and LOPA analysis. This method not only qualitatively describes the risk but also can quantify the possibility and severity of the risk, providing a more accurate assessment result.

[0034] (4) In the data collection stage, the present invention emphasizes collecting detailed system information and historical accident event statistical analysis data. These data provide a solid foundation for risk assessment, ensure that the analysis results are closer to the actual situation, improve the reliability and accuracy of risk assessment, and reduce the uncertainty based on assumptions or theoretical models.

[0035] (5) Based on the risk assessment results, the present invention proposes specific improvement measures and suggestions, including optimizing existing protective layers, adding new protective layers, and strengthening personnel training and management. These suggestions are clearly operable and feasible, not only helping to identify and assess risks, but also providing practical solutions to ensure that risks are effectively controlled and reduced.

[0036] (6) The present invention constructs a risk matrix and an accident risk severity table applicable to nuclear fuel element manufacturing facilities. In accident scenarios with relatively low casualties and property losses caused by radioactive material leakage and nuclear criticality accidents, the importance of environmental and social impacts is highlighted to prevent negligence due to the extremely low probability of accidents, which may cause social panic and international public opinion impacts. Description of the Drawings

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments, which form a part of the present invention. The schematic embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0038] Figure 1 It is a flowchart of the LOPA protective layer risk assessment method for nuclear fuel element manufacturing facilities of the present invention. Detailed Embodiments

[0039] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention in combination with specific embodiments and corresponding drawings of the present invention. In the description of the present invention, it should be noted that the term "or" is generally used in the sense of including "and / or", unless otherwise clearly specified in the content.

[0040] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a magnetic connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations. Additionally, in the description of this application, the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, or more, unless otherwise clearly and specifically limited.

[0041] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] To solve the problems existing in the prior art, the embodiments of the present application provide a LOPA protection layer risk assessment method for nuclear fuel element manufacturing facilities. Aiming at the deficiencies of the existing assessment technologies, a risk matrix applicable to nuclear fuel element manufacturing facilities is established, and management measures are used as independent protection layers to conduct semi - quantitative analysis on accident scenarios, systematically evaluate the risks of nuclear accidents / events, general industrial accidents and the risk acceptability of nuclear fuel element manufacturing facilities, and give suggestions for further reducing risks. This method can more truly reflect the risk level of nuclear accidents and avoid underestimating or overestimating the risk level of accidents.

[0043] Embodiment 1

[0044] This embodiment provides a LOPA protection layer risk assessment method for nuclear fuel element manufacturing facilities, including the following steps:

[0045] S1: Construct a risk matrix according to risk factors, risk severity and risk impact;

[0046] Different from the general chemical industry, nuclear fuel element manufacturing facilities adopt the design concept of in - depth defense in the design process. The probability of accidents is small, but due to the possible leakage of radioactive materials and nuclear critical accidents, the accident consequences may be more serious. Therefore, when constructing the risk matrix, its risk characteristics should be fully considered. This embodiment constructs a risk matrix applicable to nuclear fuel element manufacturing facilities. In the risk matrix:

[0047] 1) The risk factors consider three categories: the impact on the health and safety of staff, the impact on property losses, and the impact of radioactive accidents. They are divided into 5 levels of A, B, C, D, and E in sequence according to the severity. The classification of risk severity is shown in Table 1.

[0048] Table 1 Risk severity table

[0049]

[0050]

[0051]

[0052] 2) The possibility of an accident occurrence is divided into 7 levels from low to high, namely 1, 2, 3, 4, 5, 6, and 7.

[0053] 3) The risk levels are divided into four levels: major risk, relatively large risk, general risk, and low risk. For major risks and relatively large risks, measures should be taken to reduce the risk level. For general risks, the risk level can be further reduced in accordance with the principle of the lowest reasonable and practicable. For low risks, the existing management procedures should be implemented and the existing safety measures should be maintained in good condition and effective to prevent the risk from escalating further.

[0054] S2: Collect information on nuclear fuel element manufacturing facilities;

[0055] Collect detailed information on nuclear fuel element manufacturing facilities, including geometric parameters, process parameters, material parameters of process equipment in the system, system process instrument flowcharts, operating procedures, engineering change records, statistical analysis data of historical accident events, etc.

[0056] S3: Determine nodes based on the collected information, conduct HAZOP analysis on each node, identify potential deviations and the causes of deviations, use a risk matrix to evaluate the nodes with deviations, and screen out dangerous scenarios;

[0057] Specifically,

[0058] 1) Divide nodes for each device, process, and subsystem of the system to determine nodes.

[0059] 2) Use HAZOP analysis to determine keywords, process parameters, normal operating conditions, and guiding words for each node to determine deviations. The operating status of nuclear fuel element manufacturing facilities is divided into normal operation and anticipated operational occurrences. Anticipated operational occurrences will not cause serious damage to safety-significant items. Since they can cause internal / external irradiation to personnel, the impact of anticipated operational occurrences should be taken into account when determining deviations.

[0060] 3) For nodes with safety risks, analyze all causes of deviations, confirm relevant initiating events, and determine the frequency of event occurrence. When analyzing the causes, the impact of external events such as extreme meteorology, earthquakes, and external human events should also be considered.

[0061] 4) Analyze the consequences caused by deviations in each node, conduct risk assessment on the consequences according to the risk matrix, and evaluate the severity of the consequences, the likelihood of occurrence, and the risk level. In the consequence analysis, the environmental and social impacts caused by radioactive substances should be focused on.

[0062] 5) Classify the risks of dangerous scenarios caused by each deviation. The purpose is to help qualitatively evaluate the risk degree of deviations and thereby determine the priority level of each recommended measure in the analysis conclusion. Then, according to the risk matrix and the risk evaluation index in the matrix, classify the resulting risks as "low risk", "general risk", "relatively large risk", and "major risk".

[0063] S4: Identify the independent protection layers for hazardous scenarios, conduct LOPA analysis, and calculate the remaining accident risks and their levels after the reduction by the independent protection layers.

[0064] For the "major risks" and "significant risks" scenarios identified through HAZOP analysis, identify the independent protection layers for the accident scenarios. Based on the relevance of the initial events and whether the independent protection layers (IPLs) are shared, the combined calculation method is used to calculate the consequence frequencies caused by multiple initial events, and the impacts of enabling conditions and correction factors are fully considered to determine their failure probabilities. Calculate the remaining accident risks and their levels after the reduction by the independent protection layers. Under the premise of economy and effectiveness, propose the optimal safety countermeasures.

[0065] Specifically, in nuclear fuel element manufacturing facilities, the enabling conditions considered in LOPA analysis include aging enabling conditions (process state risks) and operation enabling conditions, and the correction factors include ignition probability, radioactive material diffusion probability, personnel exposure probability, radiation damage probability, fatality rate, etc.

[0066] The consequence frequency is calculated according to formula (1):

[0067]

[0068] In the formula:

[0069] f c Refers to the frequency of the consequence C caused by the i-th initial event, times / year;

[0070] f i I Refers to the frequency of the occurrence of the initial event i, times / year;

[0071] P i E Refers to the probability of the enabling condition occurring;

[0072] Refers to the m-th conditional correction factor of the initial event i;

[0073] PFD in Refers to the failure probability of the n-th independent protection layer of the initial event i.

[0074] For possible nuclear criticality accidents, nuclear fuel element manufacturing facilities adopt five layers of defense-in-depth measures, including conservative design, high-quality construction / commissioning and operation, setting up protection barriers, system monitoring, alarming and interlocking, fail-safe design, radioactive material containment, on-site and off-site emergency response, etc. Its independent protection layers include geometric safety (intrinsic safety design), geometric control (intrinsic safety design), concentration control and moderation control (critical alarming and personnel response), quality control and spacing control (management measures), etc.

[0075] S5: Propose safety countermeasures for the remaining accident risks and their levels until the remaining accident risks are reduced to the lowest practicable level;

[0076] The level of the remaining accident risks should be reduced to low risks. For a nuclear criticality accident, it should be ensured that the likelihood of the accident occurring is reduced to 10 -6 and below. If the existing protection layers do not meet the requirements, it is recommended to add reasonable and practicable independent protection layers to further reduce the risk level.

[0077] When the deviation occurring in step S3 is that the amount of UO 2 powder entering a single inspection hopper is too large, the LOPA analysis process and results are shown in Table 2.

[0078] Table 2 LOPA analysis process and results

[0079]

[0080]

[0081] Example 2

[0082] This example provides a LOPA protection layer risk assessment method for nuclear fuel element manufacturing facilities, including the following steps:

[0083] S1: Construct a risk matrix based on risk factors, risk severity, and risk impact;

[0084] In this example, a risk matrix applicable to nuclear fuel element manufacturing facilities is constructed. In the risk matrix:

[0085] 1) The risk factors consider three categories: the impact on the health and safety of staff, the impact on property losses, and the impact of radioactive accidents. They are classified into 5 levels of A, B, C, D, and E in sequence according to the severity, and the classification of risk severity is shown in Table 1.

[0086] Table 1 Risk severity table

[0087]

[0088]

[0089]

[0090] 2) The likelihood of the accident occurring is classified into 7 levels from low to high as 1, 2, 3, 4, 5, 6, and 7.

[0091] 3) The risk levels are divided into four levels: major risk, relatively large risk, general risk, and low risk. For major risks and relatively large risks, measures should be taken to reduce the risk level. For general risks, the risk level can be further reduced in accordance with the principle of the lowest reasonable and practicable. For low risks, the existing management procedures should be implemented and the existing safety measures should be maintained in good condition and effective to prevent the risk from escalating further.

[0092] S2: Collect information on nuclear fuel element manufacturing facilities;

[0093] Collect detailed information on nuclear fuel element manufacturing facilities, including geometric parameters, process parameters, material parameters of process equipment in the system, process instrument flowcharts of the system, operating procedures, engineering change records, statistical analysis data of historical accident events, etc.

[0094] S3: Determine nodes based on the collected information, conduct HAZOP analysis on each node, identify potential deviations and the causes of deviations, use a risk matrix to evaluate the nodes with deviations, and screen out dangerous scenarios;

[0095] Specifically,

[0096] 1) Divide nodes for each device, process, and subsystem of the system to determine nodes.

[0097] 2) Use HAZOP analysis to determine keywords, process parameters, normal operating conditions, and guiding words for each node to determine deviations. The operating states of nuclear fuel element manufacturing facilities are divided into normal operation and anticipated operational occurrences. Anticipated operational occurrences will not cause severe damage to safety - significant items. Since they can cause internal / external irradiation to personnel, the impact of anticipated operational occurrences should be taken into account when determining deviations.

[0098] 3) For nodes with safety risks, analyze all the causes of deviations, confirm relevant initiating events, and determine the frequency of event occurrence. When analyzing the causes, the impact of external events such as extreme meteorology, earthquakes, and external human events should also be considered.

[0099] 4) Analyze the consequences caused by deviations in each node, conduct risk assessment on the consequences according to the risk matrix, and evaluate the severity of consequences, the likelihood of occurrence, and the risk level. In consequence analysis, the environmental and social impacts caused by radioactive substances should be focused on.

[0100] 5) Classify the risks of dangerous scenarios caused by each deviation. The purpose is to help qualitatively evaluate the risk degree of deviations and thus determine the priority level of each recommended measure in the analysis conclusion. Then, according to the risk matrix and the risk evaluation index in the matrix, classify the resulting risks into "low risk", "general risk", "relatively large risk", and "major risk".

[0101] S4: Identify the independent protection layers for dangerous scenarios, conduct LOPA analysis, and calculate the remaining accident risks and their levels after the reduction by the independent protection layers;

[0102] For the "relatively high risks" and "major risks" scenarios identified through HAZOP analysis, identify the independent protection layers for the accident scenarios. According to the relevance of the initial events and whether the independent protection layers (IPLs) are shared, the consequence frequencies caused by multiple initial events are calculated using the comprehensive calculation method, and the impacts of enabling conditions and correction factors are fully considered to determine their failure probabilities, and calculate the remaining accident risks and their levels after the reduction by the independent protection layers. On the premise of economy and effectiveness, propose the optimal safety countermeasures.

[0103] Specifically, in nuclear fuel element manufacturing facilities, the enabling conditions considered in LOPA analysis include aging enabling conditions (process state risks) and operation enabling conditions, and the correction factors include ignition probability, radioactive material diffusion probability, personnel exposure probability, radiation damage probability, lethality rate, etc.

[0104] The consequence frequency is calculated according to formula (1):

[0105]

[0106] In the formula:

[0107] f c Refers to the frequency of the consequence C caused by the i-th initial event, times / year;

[0108] f i I Refers to the frequency of the occurrence of the initial event i, times / year;

[0109] P i E Refers to the probability of the enabling condition occurring;

[0110] Refers to the m-th condition correction factor of the initial event i;

[0111] PFD in Refers to the failure probability of the n-th independent protection layer of the initial event i.

[0112] For the possible radioactive material leakage accidents, their independent protection layers include container pressure resistance design (inherently safe design), DCS control system (BPCS), conductivity meter and HF detection and alarm (critical alarm and personnel response), accident ventilation filtration and purification system (protection measures after release), operating procedures and personnel training (management measures), etc.

[0113] S5: For the remaining accident risks and their levels, propose safety countermeasures until the remaining accident risks are reduced to the lowest feasible level;

[0114] The remaining risk level of the accident should be reduced to a low risk level. For radioactive material leakage, it should be ensured that the likelihood of the accident occurrence is reduced to 10 -6 or less. If the existing protection layer does not meet the requirements, it is recommended to add reasonable and feasible independent protection layers to further reduce the risk level.

[0115] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit of the present invention and the scope protected by the claims, and all of them belong to the protection scope of the present invention.

Claims

1. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility, characterized in that: The following steps are involved: S1: Construct a risk matrix based on risk factors, risk severity and risk impact; S2: Collect information on nuclear fuel element manufacturing facilities; S3: Determine nodes based on the collected data, conduct HAZOP analysis on each node, identify potential deviations and the causes of deviations, use the risk matrix to evaluate the nodes that cause deviations, and screen out dangerous scenarios; S4: Identify the independent protection layers of dangerous scenarios, conduct LOPA analysis, and calculate the residual risk and level of accidents after the independent protection layers are reduced; S5: Propose safety countermeasures based on the residual risk and level of the accident until the residual risk of the accident is reduced to the lowest feasible level.

2. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility according to claim 1, characterized in that: In step S1, the risk factors include the impact on the health and safety of workers, the impact on property losses, and the impact on radioactive accidents; the risk severity is divided into five levels, namely A, B, C, D, and E, and the risk impact is divided into levels 1, 2, 3, 4, 5, 6, and 7 from low to high according to the possibility of accidents.

3. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility according to claim 1, characterized in that: In step S2, the collected data include geometric parameters of process equipment, process parameters, material parameters, system process instrument flow chart, operating procedures, engineering change records and historical accident event statistical analysis data.

4. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility according to claim 3, characterized in that: Step S3 specifically includes the following steps: S31: Divide each equipment, process, and subsystem into nodes and determine the nodes; S32: Use HAZOP analysis to determine the keywords, process parameters, normal operating conditions, and guide words for each node, and then determine the resulting deviations; S33: For nodes with security risks, analyze all causes of deviation, confirm the initial event, and determine the frequency of the event; S34: Analyze the consequences of deviations at each node, conduct risk assessment on the consequences according to the risk matrix, and evaluate the severity, likelihood of occurrence, and risk level of the consequences; S35: Classify the risk of hazardous scenarios resulting from each deviation.

5. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility according to claim 4, characterized in that: In step S33, when analyzing the causes of the deviation, the impact of external events should also be considered, including extreme weather, earthquakes, and external man-made events; in step S34, when conducting a risk assessment of the consequences, the environmental and social impacts caused by radioactive substances should also be considered.

6. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility according to claim 4, characterized in that: In step S35, according to the risk matrix and the risk evaluation index in the risk matrix, the risks are divided into low risk, general risk, greater risk and major risk, and the greater risk and major risk are dangerous scenarios.

7. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility according to claim 6, characterized in that: In step S4, for the larger risk scenarios and major risk scenarios analyzed by HAZOP, the independent protection layers of the dangerous scenarios are identified, and the failure probability is determined based on the correlation of the initial events, whether the independent protection layers are shared, the frequency of consequences caused by multiple initial events, and the influence of enabling conditions and correction factors. The residual risk and level of the accident after the independent protection layers are reduced are calculated.

8. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility according to claim 7, characterized in that: In step S4, in response to nuclear criticality accidents, the nuclear fuel element manufacturing facility adopts five layers of in-depth defense measures, including conservative design, high-quality construction / commissioning and operation, setting up protective barriers, system monitoring alarms and interlocks, failure-safe design, radioactive material containment, and on-site and off-site emergency response. The independent protection layers include geometric safety, geometric control, concentration control and moderation control, quality control, and spacing control.

9. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility according to claim 7, characterized in that: In step S4, for radioactive material leakage accidents, the independent protection layer includes container pressure resistance design, DCS control system, conductivity meter and HF detection alarm, accident ventilation filtration and purification system, operating procedures and personnel training.

10. A LOPA protective layer risk assessment method for a nuclear fuel element manufacturing facility according to any one of claims 8 or 9, characterized in that: In step S5, the residual risk level of the accident should be reduced to low risk. For radioactive material leakage or nuclear criticality accident, the probability of the accident should be reduced to 10. -6 And below, if the independent protection layer does not meet the requirements, then add a reasonable and feasible independent protection layer to further reduce the risk level.

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