KR20110046091A - Importance analysis method considering the severity and the opportunity - Google Patents

Abstract

PURPOSE: An importance evaluation method considering seriousness and opportunity is provided to minimize the subjective decision of an expert and the objective evaluation of data. CONSTITUTION: An importance evaluation is determined(101). The seriousness of a system and a device is evaluated(103). The importance evaluation of the system and the device is evaluated(105). The qualitative importance of the instrument and the function is calculated by using the system and the function of the device(107). The system, the function, and the importance are evaluated(109).

Description

IMPORTANCE ANALYSIS METHOD CONSIDERING THE SEVERITY AND THE OPPORTUNITY}

The present invention relates to a method for qualitatively evaluating the importance of the systems and equipment constituting the industrial equipment in a complex industrial equipment such as a nuclear power plant, and more particularly, according to the subjectivity and experience of the evaluator performing the importance evaluation. In order to minimize judgment errors, the importance evaluation is divided into "severity evaluation" and "probability evaluation", and then the results of the two evaluations are combined to evaluate the final importance.

A materiality assessment is a list of the systems, functions, or devices that make up a facility, and an assessment of the contributions made to each of the major controls for achieving the facility's operational objectives. The results of the materiality assessment provide a basis for determining management priorities in a business environment that requires efficient operation with limited resources. Therefore, the reliability of the results of the importance evaluation has emerged as an important factor in terms of safety and economics of the facility.

Importance assessment can be divided into quantitative and qualitative methods. The quantitative method is to model the system and equipment of the facility in detail through probabilistic safety evaluation, and to calculate the effect according to a predetermined rule, so that the more accurate relative importance can be evaluated numerically. However, if the facility is complex, modeling itself is difficult, or if the facility is simple, it is inefficient in terms of cost. Therefore, in this case, a qualitative importance assessment method that utilizes the experience and knowledge of qualified professionals is used.

In the conventional qualitative importance evaluation, a Delphi evaluation method is used to synthesize opinions and draw consensus through repetitive discussions of related experts. In other words, it is a way for each expert to present an individual's opinion on the question to be discussed, collect it, and then reach a consensus point by discussing again the part where the consensus is not reached. For example, the method of evaluating the functional importance of a nuclear power plant using the Delphi method includes (1) classifying systems and functions of nuclear power plants, and (2) developing materiality assessment items that meet the purpose of operating nuclear power plant facilities. And (3) assigning scores for materiality assessment items according to each system function for each expert. (In this step, experts determine the effect and possibility of each system function on the entire facility based on their knowledge and experience. Scores), (4) coordinating opinions through expert committee meetings, and (5) determining final importance.

This qualitative importance assessment through Delphi method is an opportunity to share the knowledge and experience of experts, and has the advantage of gaining information from experience that cannot be obtained from engineering model. It can also be effective in narrowing the scope of the subjects discussed or in reaching consensus on well-known issues. However, in areas that require experts in complex and diverse fields, such as nuclear power plant facilities, the evaluation results may vary depending on the level and experience of each expert, subjectivity, disposition, etc., resulting in increased uncertainty. There is a problem that the reliability is poor.

A major source of increased uncertainty and reduced accuracy in traditional qualitative importance assessments is the need for experts in one field to consider too much information in a short time. In addition, since the information on which the evaluation is based depends entirely on the knowledge and experience of the expert, there is a high probability that false judgments and errors may exist. For example, when evaluating the functional importance of a nuclear power plant, experts evaluate the contribution of each evaluation item by comprehensively considering the role of the function and the possibility of function failure, the impact in case of failure, the presence of supporting facilities in case of failure, and the experience of failure. shall.

However, in large complex facilities where complex and diverse facilities exist, few experts have knowledge and experience in all systems and functions, and even those who are knowledgeable and experienced are likely to have errors in engineering judgments that rely on memory. Big. In addition, since the degree of determining the evaluation score may vary according to the propensity of experts, the uncertainty of the evaluation result increases.

The present invention aims to obtain more objective and accurate importance evaluation results by reducing uncertainty according to subjective judgments and inclinations of expert groups inevitably present in the existing qualitative importance evaluation.

To this end, in the present invention, in order to reduce the uncertainty of the qualitative importance evaluation, the importance evaluation is divided into a "severity evaluation" and a "occurrence evaluation", and the "severity evaluation" score and the "occurrence evaluation" score are finally used. After calculating the importance scores, the objective is to perform a final importance determination.

This object is achieved by the present invention. The present invention relates to a method for evaluating the importance of the systems, functions, and devices constituting an industrial facility in consideration of severity and likelihood. Evaluating the severity of systems, functions, and devices; evaluating the likelihood of systems, functions, and devices; severity of systems, functions, and devices; and the likelihood of occurrence of systems, functions, and devices. Calculating the qualitative importance of the system, function, and device, and determining the criticality threshold to evaluate the final importance of the system, function, and device.

In addition, in the step of evaluating the severity of the system, the function, and the device, the severity is determined in consideration of the extent to which the failure of the system, the function, and the device affects the importance evaluation item, and whether alternative means are available. Evaluate.

Further, in the present invention, evaluating the probability of occurrence of the system, the function, and the device may include estimating the failure rate of the system, the function, and the device, evaluating the multiplicity of the system, the function, and the device; Assessing the diversity of systems, functions, and devices. The likelihood is evaluated based on a failure rate evaluation result at the step of evaluating the failure rate, a multiplicity evaluation result at the step of evaluating the multiplicity, and a diversity evaluation result at the step of evaluating the diversity.

The present invention also provides a method for calculating the failure probability of a system, a function, and a device based on a failure rate, multiplicity, and diversity evaluation results, and calculating the probability of failure of the system, a function, and a device. It further comprises the step of converting to the probability of occurrence.

In the step of evaluating the failure rate, a device having a high failure rate is selected as a core device as an active device that receives driving power from the outside of the devices constituting the system or function, and the failure rate of the core device is used as the failure rate of the system or function. do.

In the step of evaluating the multiplicity, based on the success criteria of the multiplicity design and the failure rate of the core device, the probability of failure of the multiplicity design is calculated and used as a result of the multiplicity evaluation. Based on the failure rate of the standard and core equipment, the probability of malfunction of the diversity design is calculated and used as the result of the diversity evaluation.

In addition, the present invention calculates the qualitative importance of the system, the function, and the device using the system, the function, and the severity of the system, the function, and the device, the severity and the likelihood of occurrence Multiply by to calculate the qualitative importance.

In addition, in the step of determining the criticality threshold and evaluating the final importance, the present invention determines the importance threshold by converting the RRW value used as the importance measure of the probabilistic safety evaluation by Z-Value, and determining the qualitative importance as the Z-value. If the value is converted to a value above the criticality threshold, it is evaluated as high importance.

In the present invention, in order to secure the reliability of expert judgment, which is the main cause of uncertainty, expert judgment is limited to "severity evaluation", and in "probability evaluation", the possibility of occurrence is evaluated by objective information using design data and a device reliability database. The method of converting this into a score was used. As a result of measuring the improvement effect according to the present invention by the six sigma technique, the dispersion of the importance gap was greatly improved compared to the Delphi evaluation method, which is a qualitative importance evaluation method, thereby improving the process capability. For example, process capability (Zst) improved from 1.6 to 2.31, defect rates decreased from 460,000 ppm to 200,000 ppm, and DPMO improved 57%.

According to the present invention, the reliability of the results of the importance evaluation can be greatly improved by using a method of minimizing the subjective judgment of the expert and supplementing the objective evaluation based on the data, thereby reducing the management cost and enhancing the safety of the facility. . In addition, the expert committee can reduce the time spent on materiality assessment, thereby avoiding waste of human resources.

In addition, it is known that constructing a quantitative importance evaluation model in general industrial facilities including thermal power plants or chemical plants is not effective. The present invention has the advantage that it can be applied to general industrial equipment as a qualitative importance evaluation technique that can be performed when the quantitative importance evaluation model is not effective.

In the present invention, in order to reduce the uncertainty of the qualitative importance evaluation, the importance evaluation is divided into "severity evaluation" and "probability evaluation". In "severity evaluation", the evaluation based on the expert's engineering judgment should evaluate only the influence of the system, function, and equipment of the facility on the operation purpose of the entire facility in order to minimize the increase of uncertainty, and objective criteria to eliminate the uncertainty of the evaluation. To present. In the "probability assessment", the failure rate, the system and function to be evaluated, the multiplicity design of the equipment and the diversity design information are scored in the design data of the target equipment and the reliability database of the equipment. Finally, the final importance score is calculated by combining the "severity evaluation" score and the "probability evaluation" score which are the result of the engineering evaluation of the expert, and the final importance determination is performed.

Hereinafter, with reference to the accompanying drawings, a method for evaluating the importance of the system, function, and equipment constituting the industrial equipment according to the present invention will be described in detail.

1 is a flowchart of a qualitative importance evaluation method according to the present invention.

The method 100 for evaluating the importance of a system, function, and device according to the present invention includes determining the importance evaluation item (101), evaluating the severity (103), and evaluating the likelihood of occurrence (105). And calculating (107) the qualitative importance using the severity and likelihood, and determining the criticality threshold to evaluate the final importance (109).

In step 101 of determining the importance evaluation item, a list of the entire systems, functions, and devices of the target equipment is prepared, and the importance evaluation item is configured. The materiality assessment item consists of the main management items to achieve the purpose of the equipment to be evaluated and can be modified according to the characteristics of the equipment. Taking a nuclear power plant as an example, the purpose of a nuclear power plant facility is largely to secure safety and to generate stable power to prevent external leakage of radioactive material. Therefore, domestic and overseas pressurized water reactor type nuclear power plants are divided into accident response function and normal output operation function. The evaluation items related to the incident response function include the function of stopping the reactor and maintaining the safety stop state, maintaining the pressure system integrity of the reactor coolant system, removing the heat and radiation from the containment atmosphere, maintaining the health, and removing heat from the reactor. There is this. In addition, the evaluation items related to the normal output operation function include primary side heat removal function, power conversion function, primary side, secondary side and containment pressure control function, heat removal from the reactor, cooling water supply, equipment or room cooling function. It has power supply function, drive and control power supply function.

In step 103 of assessing severity, experts are called to perform a severity assessment. Experts convened in the evaluation determine the degree of influence on the above-mentioned importance evaluation items for each item in the system and function of the equipment to be evaluated and the device list, and the higher the importance is, the higher the score is assigned. Since evaluation criteria may vary from expert to expert, the objective criteria should be established to prevent the increase of uncertainty due to the distribution of severity assessment scores. Therefore, the present invention provides a severity evaluation scoring criteria as shown in Table 1. The criteria limit the range of points assigned by experts in the severity assessment from 1 to 5 points.In consideration of evaluation, the system and function to be evaluated, and the degree and substitution of the degree of impact on the above evaluation items in case of failure (loss) Only the availability of the means was considered.

2 is a flowchart illustrating a process performed in the likelihood evaluation step included in the qualitative importance evaluation method according to the present invention.

Evaluating the likelihood 105 includes evaluating a failure rate 201, evaluating multiplicity 203, evaluating diversity 205, as shown in FIG. 2, Calculating a probability of malfunctioning based on the results of the failure rate, multiplicity, and diversity evaluation (207), and converting the probability of failure into a probability of occurrence (209). In order to assess the likelihood of occurrence, it is necessary to collect information on the characteristics and design characteristics of the equipment constituting the function to be analyzed. Device failure rates can be obtained from the device-specific reliability database, and information regarding multiplicity and diversity can be obtained from the design data of the target installation.

In the step 201 of evaluating the failure rate, the failure rate of the system and the function to be evaluated and the device is evaluated. The system and function to be evaluated and the failure rate of the device can be obtained from the stochastic safety evaluation report and the device reliability data of the manufacturer's design requirements. If the system and function are subject to evaluation, the system and function are composed of a combination of devices, and among the devices constituting the system and function are active devices that receive driving power from the outside. Is used as the failure rate value of the system and function to be evaluated.

In step 203, the multiplicity of the system and the function to be evaluated and the device are evaluated. Multiplicity is the design of a separate independent train that performs the same function within a system as a homogeneous device. In the case of a critical function, even if a series of function failures is performed, the same function can be performed independently. From the design stage. Therefore, the multiplicity design information can be obtained from the schematic and design requirements of the system to be evaluated, and the multiplicity evaluation should reflect the success criteria of the multiplicity design included in the multiplicity design information. For example, if two series were designed with 100% capacity in the design, the success criterion would be 1/2, and according to this success criterion, the failure rates of the core devices for each cleavage obtained in the failure rate evaluation step 201 would be mutually different. Multiply the probability of malfunction. As another example, if three series were designed with 50% capacity each, the success criterion would be 2/3, and the probability of failure would be calculated by combining the failure rate of the core equipment (see Example 3 in Table 2). The method of calculating the failure probability is shown in Table 2 as a method commonly used in the probabilistic safety evaluation. Multiplicity assessment is assessed by confining scope within the analyte lineage and function.

In step 205 of evaluating the diversity, the diversity of the systems, functions, and devices to be evaluated is evaluated. Diversity is the design of a separate and independent series that performs the same function in one system with different kinds of equipment. When designed with the same kind of equipment, it is reflected from the design stage to prevent the possibility of simultaneous failure by the same cause. have. As with multiplicity, it is designed to perform the same function independently in case of failure of the system and functions that are important to the operation of the facility. Therefore, diversity design information can also be obtained from the design and design requirements of the system to be evaluated, and as in the multiplicity evaluation, the success criteria of diversity design should be reflected in the diversity evaluation. 3 is a design of a system for supplying water to two series of motor drive pumps (MDP-A and MDP-B) and one series of turbine drive pumps (TDP) as an example of the diversity design. In FIG. 3, two series of 100% capacity motor drive pumps correspond to multiplicity design requirements, and 100% capacity turbine drive pumps driven by steam force in response to loss of external power supply correspond to diversity designs. Diversity assessment is assessed by limiting the scope to the function to be analyzed.

In calculating the failure probability 207, the failure probability is calculated based on the results of the failure rate, multiplicity, and diversity evaluation. The method of calculating the probability of failure is generally the method used to construct the fault tree in the Probabilistic Safety Assessment (PSA).

In the step 209 of converting the probability of malfunction to a probability, the probability of malfunction is calculated in the step 207 of calculating a probability of malfunction. Since the probability of malfunction usually appears as a very small number, it is necessary to convert the probability of malfunction into an appropriate score in order to produce a final importance decision score in combination with the results of the severity assessment. Accordingly, the present invention provides a likelihood conversion table as shown in Table 3. As shown in Table 3, the score is distributed according to the range of the probability of malfunction, which is 1 point if the range of malfunction is less than 1.0E-09, 2 points if it is more than 1.0E-09 and less than 1.0E-08. 3 points for 1.0E-08 or more and less than 1.0E-07, 4 points for 1.0E-07 or more and less than 1.0E-06, 5 points for 1.0E-06 or more and less than 1.0E-05, 1.0E-05 or more 1.0E-05 6 points below 04, 7 points above 1.0E-04 and below 1.0E-03, 8 points below 1.0E-03 and below 1.0E-02, 9 points above 1.0E-02 and below 1.0E-01, or 1.0 If it is E-01 or more, it will convert into 10 possible generations.

In the step 107 of calculating the qualitative importance, the qualitative importance is calculated using the severity obtained in the severity evaluation step 103 and the likelihood obtained in the likelihood evaluation step 105. The qualitative importance value is obtained by multiplying the severity evaluation score and the likelihood conversion score as in Equation 1.

In step 109, the importance threshold is determined to evaluate the final importance. The criticality threshold is a threshold for determining high and low importance, and may be used to determine appropriate scores at the discretion of experts. However, the present invention has developed a method for determining the criticality threshold by using the RRW (Risk Reduction Worth) which is used as the importance measure of probabilistic safety evaluation. The RRW value is a statistically calculated value of the risk reduction in the case of the failure of the equipment in the probabilistic safety evaluation model. In general, the RRW value is determined to be highly important when the RRW value is more than 1.005. Since the qualitative importance value and the RRW value determined in the step 107 of calculating the qualitative importance have different calculation methods and units, a standard transformation step is required. For this purpose, Z-Value transformation, which is one of statistical techniques, is used. The Z-value transformation of the qualitative importance value is shown in Equation 2, and the Z-value transformation of the probabilistic safety evaluation RRW value is shown in Equation 3.

는 해당 기능의 정성적 중요도 값이고,

는 정성적 중요도의 평균값이고, σ는 정성적 중요도의 표준편차이다.

Where Z x is the qualitative importance Z-value of the feature,

Is the qualitative importance value of the feature,

Is the mean of qualitative importance, and σ is the standard deviation of qualitative importance.

는 해당 기능의 RRW 값이고,

는 RRW의 평균값이고, σ_RRW는 RRW의 표준편차이다.Where Z _{RRW , x} is the RRW Z-value of the function,

Is the RRW value for that feature,

Is the average value of RRW, and σ _RRW is the standard deviation of RRW.

After calculating the importance value and RRW value of relevant functions, use the above Z-Value transformation to calculate the converted value. The value corresponding to the Z-Value converted value of the RRW value 1.005 is set as the importance threshold. If the qualitative importance value is larger than the threshold, it is classified as high importance.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Also, in this specification, the singular forms are intended to include the plural forms as well, unless the context clearly indicates that the plural is not.

It will be understood from the foregoing description that the foregoing and equivalents thereof may be embodied in various forms. Therefore, while the description of the invention has been described in connection with specific embodiments, the true scope of the invention includes the following claims and any equivalents that may be contemplated per se to those skilled in the art, as described herein. It is not intended to be limited to the particular embodiment. Therefore, the present invention, which enables to secure the reliability of qualitative importance evaluation, may not be applicable to the establishment of an engineering analysis model or to inefficiently install an engineering analysis model.

1 is a flowchart of a qualitative importance evaluation method according to the present invention.

2 is a flowchart illustrating a process performed in the likelihood evaluation step included in the qualitative importance evaluation method according to the present invention.

3 is a diagram illustrating an example of diversity design in a system.

Claims (13)

As a method of evaluating the importance of the systems, functions, and devices that make up industrial facilities in consideration of severity and likelihood of occurrence, Determining an importance factor; and Assessing the severity of the system, function, and device; and Assessing the likelihood of the system, function, and device; and Calculating the qualitative importance of the system, function, and device using the severity of the system, function, and device and the likelihood of occurrence of the system, function, and device; And Determining a criticality threshold to evaluate the final importance of the system, the function, and the device; and the method of evaluating the importance of the system, function, and device of the industrial facility. The method of claim 1, In evaluating the severity of the system, the function, and the device, taking into account the extent to which the failure of the system, the function, and the device affects the importance evaluation item, and the availability of alternative means, 1 point, if loss of the analytical system, function or device does not affect the materiality assessment Loss of the analytical system, function, or device results in two points if there is a minor impact on the materiality score. Loss of the analytical system, function, or device results in a loss of some of the materiality criteria, but 3 points if 100% can be achieved through other means or functions. Loss of the analytical system, function, or device will result in the loss of the function of the materiality assessment, and 4 points if some can be achieved to some extent through other means or functions, or The loss of the analysis system, function and equipment is given 5 points when directly related to the loss of function of the evaluation items. The method of evaluating the importance of the system, function, and equipment constituting the industrial equipment, characterized in that for evaluating the severity. The method according to claim 1 or 2, Evaluating the likelihood of occurrence of the system, function, and device includes evaluating the failure rate of the system, function, and device, and based on the failure rate evaluation result in evaluating the failure rate. A method for evaluating the importance of the systems, functions, and equipment constituting an industrial facility characterized by evaluating the drawing. The method according to claim 1 or 2, Evaluating the likelihood of occurrence of the system, function, and device includes evaluating the multiplicity of the system, function, and device, and based on the result of the multiplicity assessment in evaluating the multiplicity A method for evaluating the importance of the systems, functions, and equipment constituting an industrial facility characterized by evaluating the drawing. The method according to claim 1 or 2, Evaluating the likelihood of occurrence of the system, function, and device includes evaluating the diversity of the system, function, and device, and based on the result of the diversity assessment in evaluating the diversity, A method for evaluating the importance of the systems, functions, and equipment constituting an industrial facility characterized by evaluating the drawing. The method according to claim 1 or 2, Evaluating the probability of generating the system, function, and device, Evaluating the failure rate of the system, function, and device; and Evaluating the system, functionality, and multiplicity of the instrument; And Evaluating the diversity of systems, functions, and devices; and evaluating the failure rate in the evaluating the failure rate, the multiplicity evaluation result in the evaluating the multiplicity, and evaluating the diversity. The method of evaluating the importance of the system, function, and equipment constituting the industrial equipment, characterized in that the occurrence probability is evaluated based on the result of the diversity evaluation of the apparatus. The method of claim 6, In the step of evaluating the failure rate of the system, the function, and the device, a device having a high failure rate is selected as a core device as an active device that receives a driving force from the outside of the devices configuring the system or function, and the failure rate of the core device is determined. A method for evaluating the importance of the systems, functions, and equipment constituting an industrial facility, characterized by being used as a failure rate of the system or function. The method of claim 7, wherein In the step of evaluating the multiplicity of the system, function, and equipment, an industrial equipment, characterized in that it calculates the functional failure probability of the multiplicity design based on the success criteria of the multiplicity design and the failure rate of the core equipment and use it as a result of the multiplicity evaluation Methods of assessing the importance of the systems, functions, and equipment that make up the system. The method of claim 7, wherein In the step of evaluating the diversity of the system, function, and equipment, an industrial equipment, characterized in that the functional failure probability of the diversity design is calculated based on the success criteria of the diversity design and the failure rate of the core equipment and used as a result of the diversity evaluation. Methods of assessing the importance of the systems, functions, and equipment that make up the system. The method according to claim 1 or 2, Evaluating the probability of generating the system, function, and device, Evaluating the failure rate of the system, function, and device; and Evaluating the system, functionality, and multiplicity of the instrument; and Assessing the diversity of systems, functions, and devices; and Functional failure of the system, function, and equipment based on the failure rate evaluation result at the step of evaluating the failure rate, the multiplicity evaluation result at the step of evaluating the multiplicity, and the diversity evaluation result at the step of evaluating the diversity. Calculating a probability; And Converting the probability of malfunction of the system, function, and device to the system, function, and probability of occurrence of the device; and In the step of evaluating the failure rate, a device having a high failure rate is selected as a core device as an active device that receives driving power from the outside of the devices constituting the system or function, and the failure rate of the core device is used as the failure rate of the system or function. and, In the step of evaluating the multiplicity, the failure probability of the multiplicity design is calculated based on the success criteria of the multiplicity design and the failure rate of the core device, and used as the multiplicity evaluation result. In the step of evaluating the diversity, based on the success criteria of the diversity design and the failure rate of the core equipment, the functional failure probability of the diversity design is calculated and used as a result of the diversity evaluation. And methods for assessing the importance of the device. The method of claim 10, In the step of converting the functional failure probability into the probability of occurrence of a system, a function, and a device, the range in which the functional failure probability belongs is one point less than 1.0E-09, and two if more than 1.0E-09 and less than 1.0E-08. 3 points, 1.0E-08 or more and less than 1.0E-07, 3 points, 1.0E-07 or more and less than 1.0E-06, 4 points, 1.0E-06 or more and less than 1.0E-05, 5 points, 1.0E-05 or more 1.0 6 points below E-04, 7 points above 1.0E-04 and below 1.0E-03, 8 points below 1.0E-03 and below 1.0E-02, 9 points above 1.0E-02 and below 1.0E-01, Or 1.0E-01 or more, converting into 10 possible occurrences, the method of evaluating the importance of the system, function, and equipment constituting the industrial equipment. The method of claim 11, Calculating the qualitative importance of the system, the function, and the device by using the system, the function, and the severity of the device, the system, the function, and the likelihood of the device; A method for evaluating the importance of the systems, functions, and equipment making up an industrial facility characterized by calculating the importance of sexuality. The method of claim 12, In determining the final importance by evaluating the importance threshold, the RRW value used as the importance measure of the probabilistic safety evaluation is determined by the Z-Value transformation to be the importance threshold, and the qualitative importance is converted into the Z-Value transformation. If the value is greater than or equal to the criticality, the method of evaluating the importance of the system, function, and equipment constituting the industrial equipment characterized in that the evaluation with a high degree of importance.

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