JP2022111584A - Risk impact evaluation method, risk impact evaluation device, and program - Google Patents

Abstract

To provide a method for identifying a base event or a device group having a great impact on risk.SOLUTION: A risk impact evaluation method comprises the steps of: randomly setting a failure probability for each of base events constituting a fault tree; calculating a RAW value per base event on the basis of the fault tree and the set probability; grouping base events whose RAW values are within a predetermined range; and calculating a FV importance per group of the grouped base events.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a risk impact assessment method, a risk impact assessment device, and a program for identifying risk-important devices.

A fault tree (FT: Fault Tree) may be used to model top events that may occur due to a combination of equipment failures, and perform risk evaluation. When a system including many devices such as a nuclear power plant is modeled by FT, many combinations of device failures leading to top events are generated. A combination of basic events (equipment failures, etc.) that cause a top event defined by FT is called a cutset. Analyze (detailed analysis) the probability that equipment failures contained in each cutset occur simultaneously for all cutsets generated in large numbers, and consider measures on the equipment side to prevent equipment failures from occurring at the same time. requires a lot of effort.

Patent Literature 1 describes a risk evaluation method that classifies risk items into a plurality of groups based on their degree of importance and degree of association, and calculates a risk evaluation value for each group. According to the method of Patent Literature 1, it is possible to perform risk evaluation that reflects the influence relationship between risk items.

Japanese Patent Application Laid-Open No. 2005-190402

When a large number of basic events exist, if it is possible to extract a basic event or a group of basic events that have a large impact on risk, it is possible to efficiently carry out detailed analysis and consideration of countermeasures. There is a demand for a method of identifying effective basic events for risk assessment from among a huge number of basic events.

The present disclosure provides a risk impact assessment method, a risk impact assessment device, and a program that can solve the above problems.

The risk impact evaluation method of the present disclosure includes the step of randomly setting failure probabilities for each of the basic events that make up a fault tree, and calculating a RAW value for each of the basic events based on the fault tree and the probabilities. a step of grouping the basic events whose RAW values are within a predetermined range; and a step of calculating the FV importance for each of the grouped groups.

Further, the risk impact evaluation device of the present disclosure includes a probability setting unit that randomly sets failure probabilities for each of basic events that constitute a fault tree, and a RAW value for each basic event that is applied to the fault tree and the probability. a grouping unit for grouping the base events whose RAW values are within a predetermined range; an FV importance calculation unit for calculating the FV importance for each of the grouped groups; Prepare.
have

Further, the program of the present disclosure provides a computer with a step of randomly setting failure probabilities for each of basic events that make up a fault tree, and calculating a RAW value for each of the basic events based on the fault tree and the probability. a step of calculating, a step of grouping the basic events having the RAW values within a predetermined range, and a step of calculating the FV importance for each of the grouped groups.

According to the risk/impact evaluation method, the risk/impact evaluation apparatus, and the program described above, risk-important devices and basic events can be specified.

1 is a block diagram showing an example of a risk impact assessment device according to an embodiment; FIG. It is a figure which shows an example of a fault tree. FIG. 2B illustrates a cutset for the fault tree of FIG. 2A; FIG. 10 is a diagram illustrating setting of probability to a base event and calculation of a RAW value according to the embodiment; It is a figure explaining the grouping which concerns on embodiment. It is a figure which shows an example of the risk-evaluation model using the group which concerns on embodiment. It is a figure which shows an example of the grouping process which concerns on embodiment. It is a figure which shows an example of the group integration process which concerns on embodiment. 6 is a flowchart illustrating an example of risk impact evaluation processing according to the embodiment; It is a figure which shows an example of the hardware constitutions of the risk impact evaluation apparatus of embodiment.

<Embodiment>
The risk impact assessment method of the present disclosure will be described below with reference to FIGS. 1 to 8. FIG.
(Constitution)
FIG. 1 is a block diagram showing an example of a risk impact assessment device according to an embodiment.
The risk impact assessment device 10 includes an FT information acquisition unit 11, a probability setting unit 12, a RAW value calculation unit 13, a grouping unit 14, an FV importance calculation unit 15, a group selection unit 16, and an output unit 17. , and a storage unit 18 .

The FT information acquisition unit 11 acquires FT (fault tree) information. FT is a risk assessment model that expresses the relationship of combinations of basic events that cause top events by means of a tree structure. A top event is, for example, a severe accident event in a nuclear power plant. A base event is an individual accidental event that leads to a top event, such as a pump failure to start, a check valve failure to open, or a component fire in a control panel. Reference is now made to FIGS. 2A and 2B. An example of FT is shown in FIG. 2A. In the FT of FIG. 2A, the basic event A1 is the failure of the device A, the basic event B1 is the failure of the device B, the basic event C1 is the failure of the device C, and the basic event D1 is the failure of the device D. In FT of FIG. 2A, when any of basic event A1, basic event B1, and basic event C1 occur simultaneously, or when basic event D1, basic event B1, and basic event C1 occur simultaneously, the top event occurs. indicates that FIG. 2B shows the cutset of the FT of FIG. 2A. A cutset is a combination of one or more base events that give rise to a top event. The cut set in this example includes (1) a combination of basic event A1 and basic event B1, (2) a combination of basic event A1 and basic event C1, (3) a combination of basic event D1 and basic event B1, (4) a basic A combination of event D1 and basic event C1. For example, for cutset (1), the top event TE occurs when base event A1 and base event B1 occur simultaneously. The FT information acquisition unit 11 acquires FT structure information as exemplified in FIG. 2A as FT information. This structural information includes information defining a tree structure, such as that basic event B1 and basic event C1 are connected in FT by an OR gate, and basic event A1 and basic events B1 and C1 are connected by an AND gate. The FT information acquisition unit 11 also acquires the occurrence probabilities (actual occurrence probabilities) of the basic events A1 to D1 as FT information. The occurrence probabilities of the basic events A1 to D1 are set in advance based on the analysis results of a knowledgeable engineer. The FT illustrated in FIG. 2A will be described below as an example.

The probability setting unit 12 randomly sets probabilities for each of the FT basic events A1 to D1 acquired by the FT information acquisition unit 11 . In general, PRA (Probabilistic Risk Assessment) and the like perform risk assessment based on the actual probability of occurrence of a cutset. The actual probability of occurrence of a cutset is often set based on the actual value of the probability of occurrence of the basic event that constitutes the cutset, the failure rate of equipment related to the basic event, and the like. Therefore, for example, when device A and device D are of the same type, similar values are often set for the occurrence probabilities of basic event A1 and basic event D1. On the other hand, the probability setting unit 12 sets a probability of an arbitrary value for each cutset by, for example, generating a random number regardless of the contents of the basic events that make up the cutset. Now refer to FIG. The upper part of the table 100 shown in FIG. 3 shows the failure probabilities of the devices A to D. The failure probabilities of the devices A to D are the occurrence probabilities of the basic events A1 to D1, respectively. The probability setting unit 12 generates random numbers and calculates failure probabilities of the devices A to D. FIG. For example, the probability setting unit 12 calculates a random number “2.10E-05” and sets it as the failure probability of the device A, and calculates a random number “7.40E-06” and sets it as the failure probability of the device B. FIG. If the generated random number is an excessively low value (when the random number is equal to or less than the threshold value), the probability setting unit 12 generates a random number again so that the cutset containing each basic event is not cut off, and is set as the failure probability (probability of occurrence of basic event).

The RAW value calculator 13 calculates RAW values (Risk Achievement Worth) of the basic events A1 to D1. The RAW value is also called risk increase value and can be calculated by the following formula (1).
RAWi=P(TOP/i=1)/P(TOP) (1)
where P(TOP) represents the unavailability of the system (the probability of a top event occurring). Also, P(TOP/i=1) represents the unavailability of the system when the failure probability of element i becomes 1 (that is, when element i fails). RAWi is a measure of the incremental unavailability of the system when element i of the system fails. The element i is, for example, any one of the devices A to D. Since RAWi represents the increased amount of risk when element i fails, it is effective in grasping the impact of risk mitigation of equipment. The RAW value calculator 13 calculates the RAW value for each of the devices A to D when each device fails. The lower part of the table in FIG. 3 shows the RAW values when it is assumed that the devices A to D fail in the FT in FIG. 2A with the probability shown in the upper part of the table in FIG. For example, in calculating the RAW value of basic event A1, P(TOP/i=1) is the probability that device B or device C will fail from the structure of FT in FIG. 2A. P(TOP) is the probability that one of the devices A to D will fail. The RAW value calculation unit 13 uses the probabilities randomly set for the basic events A1 to D1 by the probability setting unit 12 to calculate the RAW value "3.52E+04" of the basic event A1 from FT and equation (1). Similarly, the RAW value calculator 13 calculates the RAW values of the basic events B1 to D1. As shown in the lower part of Table 100, the RAW values of basic events B1 to D1 are "3.52E+04", "1.76E+03", and "1.76E+03", respectively.

Based on the RAW values calculated by the RAW value calculation unit 13, the grouping unit 14 groups the basic events A1 to D1 according to the RAW values that are close to each other. In the case of the table 100 of FIG. 3, the grouping unit 14 groups the basic event A1 and the basic event D1 into the same group because the RAW values match at "3.52E+04". Also, since the RAW values match at "1.76E+03", the grouping unit 14 groups the basic event B1 and the basic event C1 into the same group. The result of grouping by the grouping unit 14 is shown in FIG. 4A. For convenience, the group of basic events A1 and D1 is group 1, and the group of basic events B1 and C1 is group 2. Grouping the elementary events allows the original FT to be rewritten with a more concise structure. FIG. 4B shows a simple FT obtained by rewriting the FT of FIG. 2A using groups 1 and 2 of this example. According to the FT in FIG. 4B, when a device failure in group 1 (failure in either device A or D) and a device failure in group 2 (failure in either device B or C) occur at the same time, a top event occurs. You can easily understand what to do.

For example, in the case of FT in FIG. 2A, theoretically, even if the probability setting unit 12 sets the probability of each base event completely randomly, the RAW values of the base event A1 and the base event D1 match. The RAW values of event B1 and base event C1 match. However, due to the influence of random numbers, errors may occur in the RAW values of the basic events A1 and D1 and the RAW values of the basic events B1 and C1. Also, due to the influence of random numbers, the RAW values of basic events that should belong to other groups may come close to each other by chance. Therefore, in the present embodiment, the probability setting unit 12 attempts to calculate the probability multiple times for one basic event, and the RAW value calculation unit 13 calculates the RAW value for each of the multiple probabilities. That is, a plurality of RAW values are calculated for one basic event. The grouping unit 14 groups, for example, basic events having close RAW values into the same group each time, based on a plurality of RAW values.

An example of grouping processing is shown in FIG. INST_001, 002, CABLE_001, 002, 100, 101, 102, 200, 201, 202, 310, 311, 312, and VALVE_100, 200 in Table 101 of FIG. 5 are base events, respectively. In the example of FIG. 5, setting of probabilities and calculation of RAW values based on the probabilities are executed five times for each basic event. For example, in the first trial, the RAW values of INST_001 and CABLE_001 match, the RAW values of INST_002 and CABLE_002 match, the RAW values of VALVE_100 and CABLE_100, 101, 102 match, and the RAW values of VALVE_200 and CABLE_200, 201, 202 match. RAW values match. The grouping unit 14 puts them together into one temporary group. Temporary groups G1, G2, G3, and G4 are arranged in this order. For example, if the basic events are similarly classified into temporary groups G1, G2, G3, and G4 through five times, the grouping unit 14 finally sets them as one group. Groups G_001, G_002, G_003, and G_004 are arranged in order.

Also, in the first and fifth trials, the RAW value of CABLE_301 differs from the others, and the RAW values of CABLE_310, 311, and 312 match. As a result, the grouping unit 14, for example, classifies CABLE_301 into temporary group G5, and classifies CABLE_310, 311, and 312 into temporary group G6. In the second trial, the RAW values of CABLE_301, 310, 311, 312 match. The grouping unit 14 classifies CABLE_301, 310, 311, and 312 into temporary group G5. Finally, the grouping unit 14 sets CABLE_310, 311, and 312 with matching RAW values as one group G_006 and sets CABLE_301 as one group G_005 through the five times.

Logically, the RAW values are consistent for underlying events with similar risk impact. However, when the number of basic events is enormous, the work of analyzing the structure of FT and grouping the basic events is costly. On the other hand, in the present embodiment, the RAW values calculated based on the occurrence probabilities of the randomly set basic events are used to put together the basic events having similar RAW values into one group. This enables grouping of a large number of basic events with similar risk impacts by simple calculation without analyzing the structure of the FT. Moreover, by randomly setting probabilities for basic events, for example, different arbitrary probabilities are set for failures of the same type of equipment, and RAW values are calculated based on the values. As a result, regardless of the type of device, it is possible to group devices that can be treated in the same way from the viewpoint of risk impact in terms of the fault tree structure.

The FV importance calculator 15 calculates FV (Fussell-Vesely) importance for each group created by the grouping unit 14 . The FV importance can be calculated by the following formula (2).
FVi=Pi(TOP)÷P(TOP) (2)
where P(TOP) represents the unavailability of the system, and Pi(TOP) is the unavailability of the system when the probability of failure of element i becomes 0 (that is, when element i has not failed). and system unavailability (=P(TOP)). The FV importance indicates the proportion of the probability of a top event occurring that is caused by the failure of element i. is large. The FV importance is used, for example, to grasp the effectiveness of countermeasures for devices in the system. Further, the FV importance calculation unit 15 does not calculate the FV importance for the devices A to D, but calculates the FV importance for all the devices grouped by the grouping unit 14 . For example, for group 1, the FV importance calculation unit 15 calculates the difference between the unavailability of the system when both device A and device D are not malfunctioning and P(TOP) as Pi(TOP) in equation (2). to calculate the FV importance. In other words, the FV importance calculation unit 15 calculates how much the risk is reduced when both the devices A and D are not malfunctioning (when both the basic events A1 and D1 do not occur) compared to the other case. Calculated by (2). Note that unlike the grouping process, the FV importance calculation unit 15 calculates the FV importance of group 1 based on the actual failure rates of devices A and D (actual occurrence probabilities of basic events A1 and D1). calculate. For example, the FV importance calculation unit 15 calculates the FV importance of group 1 based on the actual probability of occurrence of each primitive event included in the FT information acquired by the FT information acquisition unit 11 . Similarly, the FV importance calculation unit 15 calculates the degree of risk reduction (FV importance) for group 2 when both device B and device C are not malfunctioning. Note that when the calculated FV importance is not a significant value, the FV importance calculation unit 15 integrates groups and calculates the FV importance for a larger group after integration. An example of integrating groups will be described with reference to FIG.

Table 102 in FIG. 6 shows the FV importance calculated for each group G_001 to G_006 created by the grouping process described in FIG. The FV importance of G_003 is "1.19E-01", the FV importance of G_004 is "2.22E-16", and 0 for the other groups. For example, the FV importance calculation unit 15 compares the FV importance of each group with a predetermined threshold, and determines that if the calculated FV importance is equal to or less than the threshold, no significant value is obtained. are integrated, and the FV importance is similarly calculated for the group after integration. An example of group and FV importance after integration is shown in Table 103 of FIG. For example, the FV importance calculation unit 15 creates all patterns for combinations of two of the groups G_001 to G_006, and calculates the FV importance for each. The FV importance calculation unit 15 compares all FV importance including the post-integration group with the threshold, and determines whether a significant value is obtained. For example, the FV importance calculation unit 15 compares the FV importance "6.87E-01" of the group G_003+G_004 with the threshold. Assume that the FV importance levels shown in Table 103 are all equal to or less than the threshold. Then, the FV importance calculation unit 15 further integrates the groups and calculates the FV importance again. For example, the FV importance calculation unit 15 may create all combinations of created groups and calculate the FV importance, as in the previous example. Alternatively, as the number of groups increases, the amount of calculation becomes enormous, so focusing on the constituent elements of groups with high FV importance (for example, the constituent elements of group G_003+G_004 with the highest FV importance are G_003 and G_004). Group consolidation may be implemented. For example, constituent elements of a predetermined number of groups with higher FV importance may be combined, or constituent elements of groups whose FV importance is greater than or equal to a predetermined value may be combined. . Table 104 shows an example of calculating the FV importance by additionally combining the constituent elements of the group with the highest ranking. For example, the FV importance calculation unit 15 calculates the degree of risk reduction (FV importance) for the integrated group G_003+G_004+G_001 assuming that there is no equipment failure belonging to this group. The FV importance calculation unit 15 performs group integration and FV importance calculation until a significant value is obtained.

The group selection unit 16 rearranges the groups in descending order of the FV importance value, and selects the group with the highest ranking. A group with a large FV importance value is a group of basic events that have a large impact on risk (risk-important). The group selection unit 16 may select a predetermined number of groups in descending order of FV importance, or may select groups whose FV importance is equal to or greater than a predetermined threshold. In the example of FIG. 4A, the group selection unit 16 selects group 1 and group 2, for example. In the case of table 104 in FIG. 6, group selection unit 16 selects, for example, the top two groups.

The output unit 17 outputs the result of grouping by the grouping unit 14, the FV importance calculated for each group, the groups selected by the group selection unit 16, and the like to a display device, an electronic file, or the like.
The storage unit 18 stores information necessary for selecting a group of risk-important basic events. For example, the storage unit 18 stores FT information acquired by the FT information acquisition unit 11 .

(motion)
Next, the operation of the risk impact assessment device 10 will be described with reference to FIG.
FIG. 7 is a flowchart illustrating an example of risk impact evaluation processing according to the embodiment.
First, the FT information acquisition unit 11 acquires information on the FT to be evaluated (step S10). The FT information acquisition unit 11 records FT information in the storage unit 18 .

Next, the probability setting unit 12 randomly sets a probability for each basic event of FT acquired in step S10 (step S11). The probability setting unit 12 analyzes the FT information stored in the storage unit 18, extracts the base event, randomly generates a random number for each base event, and sets the random number as the probability of occurrence of the base event. do. If the random number is less than the predetermined reference value, the probability setting unit 12 generates the random number again. Also, the probability setting unit 12 sets the probability multiple times for one basic event. For example, the probability setting unit 12 sets five probabilities for each of the basic events A1 to D1. The probability setting unit 12 associates the set probabilities with the target basic events, and records them in the storage unit 18 for each number of trials (for example, the probabilities set for the first time to the probabilities set for the fifth time separately).

The RAW value calculator 13 calculates the RAW value of each basic event (step S12). For example, the RAW value calculation unit 13 calculates five RAW values using each of the five probabilities set for the basic event A1 and Equation (1) based on the FT obtained in step S10. do. The RAW value calculator 13 also calculates five RAW values for each of the basic events B1 to D1. The RAW value calculation unit 13 associates the calculated RAW value with the target basic event, and calculates the RAW value based on the probability set for each trial (for example, the RAW value based on the probability set for the first time to the RAW value based on the probability set for the fifth time). values separately) in the storage unit 18 .

Next, the grouping unit 14 groups basic events having close RAW values (step S13). For example, the grouping unit 14 groups the basic events in which the differences in the RAW values of the same number of trials are all within a predetermined range through five trials as the same group. The number of basic events belonging to one group is not limited, and may be one or three or more. Also, there is no limit to the number of groups that can be created.

Next, the grouping unit 14 determines whether or not a consistent grouping result has been obtained (step S14). For example, if the number of groups created in each of the first to fifth trials and the basic events that make up each group are all different, the grouping unit 14 determines that grouping results with unity cannot be obtained. . For example, as in the example shown in FIG. 5, when the results of grouping four times out of five are the same, the grouping unit 14 determines that a consistent grouping result has been obtained. If a consistent grouping result cannot be obtained (step S14; No), the processing of steps S11 to S14 is performed again.

If a grouping result with unity is obtained (step S14; Yes), the FV importance calculation unit 15 calculates the FV importance of each group for each group indicated by the grouping result with unity (step S15 ). The FV importance calculation unit 15 uses the actual occurrence probabilities of the basic events belonging to each group to calculate the sum of the contributions to the risk occupied by the basic events belonging to the group (all Calculate the degree of risk reduction when the underlying event does not occur). The FV importance calculation unit 15 records the calculated FV importance in the storage unit 18 .

The FV importance calculation unit 15 compares the FV importance with a predetermined threshold to determine whether a significant result is obtained (step S16). If no significant result is obtained (step S16; No), the groups are integrated as described with reference to FIG. 6 (step S17). For example, the FV importance calculation unit 15 selects a group having a high FV importance, selects two groups from the selected groups, and creates all patterns of combinations that are integrated. Then, the FV importance calculation unit 15 calculates the FV importance for the group after integration (step S15), and determines whether or not a significant result is obtained (step S16). The FV importance calculation unit 15 repeats the processes of steps S17, S15, and S16 until a significant result is obtained.

If a significant result is obtained (step S16; Yes), the group selection unit 16 selects the group with the highest FV importance as the risk-important group (step S18). Next, the output unit 17 outputs the group selected by the group selection unit 16 (step S19). For example, in the case of FIG. 6, the group selection unit 16 outputs "G_003+G_004+G_001" and "G_003+G_004+G_002" and basic events belonging to each group. In addition to the group selected in step S18, the output unit 17 may also output, for example, the finally created group, the FV importance of that group, and a list of basic events that make up each group. good.

As described above, according to the present embodiment, by using the indicators (RAW, FV importance) used in importance analysis in PRA, among a large number of basic events, from the viewpoint of impact on risk Elementary events that can be handled can be grouped together. In addition, it is possible to extract a risk-important group from among a plurality of groups. This enables efficient risk assessment by prioritizing detailed analysis and consideration of countermeasures for basic events belonging to risk-important groups.

In addition, by grouping basic events that have the same degree of risk impact, FT consisting of a large number of basic events is simplified into a group-based risk assessment model (e.g., FT in Figure 4B). We can then determine which groups are risk material. Also, according to the simplified risk evaluation model, it is possible to grasp the combination of groups that have a large impact on the risk if they fail at the same time. As a result, it is possible to efficiently analyze which devices fail at the same time leading to a peak event, and to efficiently consider facility measures to prevent a peak event from occurring. For example, when fire risk in a nuclear power plant is evaluated probabilistically (fire PRA), if fire occurs in both equipment A and equipment B, if fire occurs in equipment A and equipment C, equipment A ~ In some cases, such as when a fire breaks out at C, all combinations of equipment A to D are created, and detailed analysis and equipment support are examined for each combination. Although it is sufficient if the number of devices is about four, the number of devices provided in a nuclear power plant is enormous, and it is difficult to perform detailed analysis and the like for all combinations of devices. According to this embodiment, it is possible to identify a group of devices (basic events) that have a large risk impact. , the detailed analysis can be made more efficient. Also, as illustrated in FIG. 4B, according to this embodiment, the original FT can be simplified and modeled. For example, according to the simplified risk evaluation model, it is easy to understand that it is important to prevent simultaneous failures of Group 1 and Group 2. By grasping the groups in which the top event occurs when failures occur at the same time and considering measures to prevent the failures of equipment belonging to those groups from occurring at the same time, it is possible to efficiently implement effective equipment responses. can.

In addition, in conventional fire risk assessment, a nuclear power plant is divided into sections, and if a fire breaks out in one piece of equipment in the section, risk assessment is often performed assuming that the entire section has caught fire. Overly conservative evaluation results were often obtained. On the other hand, according to the present embodiment, risk assessment can be performed effectively by narrowing down the devices belonging to the risk-important group, so that risk assessment and countermeasures can be considered more precisely. Note that the application of the risk impact assessment of the present embodiment is not limited to fire risk assessment.

Both the RAW value and the FV importance are indexes used for risk evaluation, but generally, the magnitude of risk is often evaluated by comparing these values with a certain reference value. On the other hand, in the present embodiment, the basic events are grouped based on the RAW value, which is an index indicating the increased risk when the device fails. In addition, for each group of the grouped basic events, the FV importance, which is an index indicating the risk reduction when the device does not fail, is calculated, and the group with a large value of the FV importance is selected. In this way, in this embodiment, by using a combination of general indicators, the FT, which consists of a large number of basic events, is simplified into a model with groups as units, and which group is a risk You can decide if it is important.

FIG. 8 is a diagram illustrating an example of the hardware configuration of the risk impact evaluation device of the embodiment;
A computer 900 includes a CPU 901 , a main memory device 902 , an auxiliary memory device 903 , an input/output interface 904 and a communication interface 905 .
Each of the risk impact assessment devices 10 described above is implemented in a computer 900 . Each function described above is stored in the auxiliary storage device 903 in the form of a program. The CPU 901 reads out the program from the auxiliary storage device 903, develops it in the main storage device 902, and executes the above processing according to the program. Also, the CPU 901 secures a storage area in the main storage device 902 according to the program. In addition, the CPU 901 secures a storage area for storing data being processed in the auxiliary storage device 903 according to the program.

A program for realizing all or part of the functions of the risk impact assessment apparatus 10 may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read and executed by a computer system. The processing by each functional unit may be performed by . The "computer system" here includes hardware such as an OS and peripheral devices. The "computer system" also includes the home page providing environment (or display environment) if the WWW system is used. The term "computer-readable recording medium" refers to portable media such as CDs, DVDs, and USBs, and storage devices such as hard disks incorporated in computer systems. Further, when this program is distributed to the computer 900 via a communication line, the computer 900 receiving the distribution may develop the program in the main storage device 902 and execute the above process. Further, the program may be for realizing part of the functions described above, or may be capable of realizing the functions described above in combination with a program already recorded in the computer system. . The risk impact assessment apparatus 10 may be configured by a plurality of computers 900 that can communicate with each other.

Although several embodiments of the present disclosure have been described above, all these embodiments are provided by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

<Appendix>
The risk impact assessment method, risk impact assessment device, and program described in each embodiment are understood, for example, as follows.

(1) The risk impact evaluation method according to the first aspect includes the steps of randomly setting failure probabilities for each of the basic events A1 to D1 constituting the fault tree (FIG. 2A) (S11); Based on the fault tree and the probability (S12), the step of grouping the basic events in which the RAW value is within a predetermined range (S13), and each of the grouped groups and (S15) calculating the FV importance of .
As a result, even when there are a large number of devices and basic events to be evaluated, it is possible to group those that can be treated in the same way from the viewpoint of risk impact. By calculating the degree of FV demand for each group, the degree of influence of each group on risk can be evaluated. By referring to the degree of impact on the risk of each group, it is possible to comprehend the basic events that are effective for risk assessment. By grouping the elementary events, the original FT can be modeled into a simple form. This facilitates identification of a combination leading to a top event among many combinations of equipment failures. These enable efficient risk assessment based on FT.

(2) The risk impact assessment method according to the second aspect is the risk impact assessment method of (1), further comprising a step (S18) of selecting groups whose FV importance is equal to or greater than a predetermined value.
This makes it possible to identify groups of basic events that have a large impact on risk from among a huge number of combinations of basic events. By understanding basic events that have a large impact on risk, detailed analysis can be performed with little effort, and failure countermeasures can be considered with little effort.

(3) The risk impact assessment method according to the third aspect is the risk impact assessment method of (1) to (2), wherein when the FV importance is less than a predetermined threshold, the groups are integrated, and , to calculate the FV importance.
If the FV importance is not a significant value, the groups are integrated and the FV importance is calculated again, thereby creating and extracting risk-important groups.

(4) A risk impact assessment method according to a fourth aspect is the risk impact assessment method of (1) to (3), wherein in the step of setting the probability, a random number is generated for the base event and the probability In the step of performing the process of setting a plurality of times and calculating the RAW value of the base event, in the step of calculating the RAW value for each of the plurality of probabilities set by performing the process a plurality of times and grouping, Grouping is performed based on the plurality of calculated RAW values.
By setting the probability multiple times and calculating the RAW value, it is possible to eliminate the influence of randomly setting the probability (for example, the RAW values being close to each other by chance).

(5) The risk impact assessment method according to the fifth aspect is the risk impact assessment method of (1) to (4), wherein in the step of calculating the FV importance, the basic events classified into the groups are Calculate the degree of reduction in risk if none occur.
Evaluate the impact on the risk of the entire group by calculating the FV importance based on the difference in the probability of reaching the top event when all the failure probabilities of the basic events belonging to the group are 0 and when they are not. can be done.

(6) The risk impact assessment method according to the sixth aspect is the risk impact assessment method of (1) to (5), wherein the fault tree is a apex that occurs when a fire occurs in equipment provided in a nuclear power plant. A fault tree that models an event.
The risk impact assessment method of the present embodiment is effective in fire risk assessment for each combination of a large number of devices provided in a nuclear power plant. For example, by performing the process shown in Fig. 7 on a fault tree for evaluating the risk of fire in each piece of equipment installed in a nuclear power plant, combinations of equipment that have a large impact on fire risk are extracted. can do.

(7) The risk impact assessment device 10 according to the seventh aspect includes a probability setting unit 12 that randomly sets failure probabilities for each of the basic events that constitute a fault tree, and a RAW value for each basic event that is set to the fault A RAW value calculation unit 13 that calculates based on the tree and the probability, a grouping unit 14 that groups basic events whose RAW values are within a predetermined range, and an FV that calculates the FV importance for each of the grouped groups. and an importance calculation unit 15 .

(8) The program according to the eighth aspect provides the computer 900 with a step of randomly setting failure probabilities for each of the basic events that make up a fault tree; A step of calculating based on the probability, a step of grouping the basic events having the RAW values within a predetermined range, and a step of calculating the FV importance for each of the grouped groups are executed.

10... Risk impact assessment device 11... FT information acquisition unit 12... Probability setting unit 13... RAW value calculation unit 14... Grouping unit 15... FV importance calculation unit 16... Group selection unit 17 output unit 18 storage unit 900 computer 901 CPU,
902 Main storage device,
903 Auxiliary storage device,
904 input/output interface 905 communication interface

Claims (8)

randomly setting failure probabilities for each of the elementary events that make up the fault tree;
calculating a RAW (Risk Achievement Worth) value for each of the base events based on the fault tree and the probability;
a step of grouping the base events whose RAW values are within a predetermined range;
a step of calculating FV (Fussell-Vesely) importance for each of the grouped groups;
risk impact assessment method. 2. The risk impact assessment method according to claim 1, further comprising the step of selecting said groups whose FV importance is equal to or greater than a predetermined value. if the FV importance is less than a predetermined threshold, integrate the group and calculate the FV importance again;
The risk impact evaluation method according to claim 2. In the step of setting the probability, a process of generating a random number and setting the probability for the base event is executed a plurality of times;
In the step of calculating the RAW value of the base event, calculating the RAW value for each of the plurality of probabilities set by performing a plurality of times;
In the grouping step, grouping is performed based on the plurality of calculated RAW values;
The risk impact assessment method according to any one of claims 1 to 3. In the step of calculating the FV importance, calculating the degree of reduction in risk when none of the basic events belonging to the group occur,
The risk impact assessment method according to any one of claims 1 to 4. The fault tree is a fault tree that models a top event that occurs when a fire occurs in equipment provided in a nuclear power plant.
The risk impact evaluation method according to any one of claims 1 to 5. a probability setting unit that randomly sets failure probabilities for each of the basic events that make up the fault tree;
a RAW value calculator that calculates a RAW (Risk Achievement Worth) value for each of the basic events based on the fault tree and the probability;
a grouping unit that groups the base events whose RAW values are within a predetermined range;
an FV importance calculation unit that calculates the FV importance for each of the grouped groups;
A risk impact assessment device comprising: to the computer,
randomly setting failure probabilities for each of the elementary events that make up the fault tree;
calculating a RAW (Risk Achievement Worth) value for each of the base events based on the fault tree and the probability;
a step of grouping the base events whose RAW values are within a predetermined range;
a step of calculating the FV importance for each of the grouped groups;
program to run.

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