KR102578948B1 - Decision method of severity on consequence analysis for Postulated Initiating Events (PIEs) - Google Patents

Abstract

The present invention relates to a method for determining the severity of a nuclear power plant by function, comprising: establishing standards for determining the severity of a nuclear power plant when a function fails; collecting initial virtual events of the nuclear power plant; Deriving radiation emission values upon functional failure from the collected initial virtual events; comparing the derived radiation emission value with the reference; and listing the comparison results by function.

Description

Determination method of severity on consequence analysis for Postulated Initiating Events (PIEs)}

The present invention relates to a method for determining the severity of radiation consequences for an initial hypothetical event.

Existing safety function levels are classified according to the ANSI standard deterministic method. In the development process of a nuclear power plant, a new functional classification process is performed according to the importance of safety functions. Specifically, detailed functions are identified and an initial virtual event scenario is developed according to the power plant status.

Based on the identified functions and initial hypothetical events, a radiological conclusion analysis is performed to determine the level of radiation emission upon failure of each detailed function. Considering the currently identified features and the types of initial hypothetical events selected, the number of radioactivity analysis analyzes is required at least several thousand times.

Conclusion analysis requires a lot of time and effort because key design variables and related assumptions must be collected, entered, and analyzed for each case. In order to efficiently perform this conclusion analysis, only representative accidents can be selected and analyzed based on engineering judgment and experience, but it is difficult to determine the severity of radiation consequences by function with a high level of confidence.

Korean Patent Publication No. 2014-0055294 (published on May 9, 2014)

Therefore, the purpose of the present invention is to provide a method for determining the severity of radiation consequences for an initial hypothetical event.

The object of the present invention is to provide a method for determining the severity of each function of a nuclear power plant, comprising the steps of: establishing a standard for determining the severity of a nuclear power plant when a function fails; collecting initial virtual events of the nuclear power plant; Deriving radiation emission values upon functional failure from the collected initial virtual events; comparing the derived radiation emission value with the reference; and listing the comparison results by function.

After the collection, the method may further include determining an accident type of the initial virtual event.

The above accident types may include process accidents and equipment damage accidents.

After determining the accident type, a step of deriving a radiation emission path for each accident type may be further included.

In the step of deriving the radiation emission value, the degree of radiation emission through the radiation emission path can be calculated.

In the step of deriving the radiation emission value, factors affecting the radiation outcome at the time of the accident may be considered.

The derivation of the radiation emission value is performed using an analysis code, and the factors may include at least one of nuclear fuel damage rate, radioactive material nuclides, radioactive material status, radioactive material processing method, and efficiency of waste disposal systems and devices.

A step of determining the severity of the ending for each function from the list may be further included.

According to the present invention, a method for determining the severity of radiation consequences for an initial hypothetical event is provided.

1 is a flowchart of a decision method according to an embodiment of the present invention,
Figure 2 shows an example of the radiation gun ending level and evaluation criteria in the decision method according to an embodiment of the present invention.
Figure 3 shows an example of severity evaluation in the decision method according to an embodiment of the present invention.
Figure 4 shows the emission levels for each accident collected and listed by function in the determination method according to an embodiment of the present invention.

The present invention seeks to develop a method for determining the severity of radiation consequences by setting emission paths for each type of initial virtual event and utilizing variables that have a significant impact on emission. This improves the reliability and quality of the severity results determined. Additionally, the number of cases requiring detailed analysis is minimized, saving a lot of time and effort.

The present invention will be described in detail below with reference to the drawings.

Figure 1 is a flowchart of a decision method according to an embodiment of the present invention, Figure 2 shows an example of the radiation gun ending level and evaluation criteria in the decision method according to an embodiment of the present invention, and Figure 3 is a flow chart of the decision method according to an embodiment of the present invention. An example of severity assessment is shown in the decision method according to an embodiment of the present invention, and Figure 4 shows the emission levels for each accident collected and listed by function in the decision method according to an embodiment of the present invention.

Each step of the present invention described below can be performed using a computer and communication means (intranet, Internet, etc.).

First, a standard is established to determine the severity of the outcome when a function fails (S100).

Limits and levels of radiation consequences in the event of functional failure for each event are determined using local regulatory standards, international guidelines, and engineering judgment as input. The grades that determine the ending level are, for example, classified as serious, normal, and low.

An example of the limits and grades of radiation consequences in case of functional failure for each event is shown in Figure 2.

In other embodiments, the standards for this step are prepared through a separate process, in which case this step may be omitted.

Next, initial virtual events of the nuclear power plant are collected (S200).

The initial virtual event can be identified for each nuclear power plant, for example, the nuclear power plant being designed. Initial virtual events should be collected by power plant status, and all cases should be assumed to ensure that they are as accurate as possible.

The initial virtual event is PIE (Postulated Initiating Event), and it applies to all transient states (accidents/events) that occur in a normal state.

Plant conditions may include normal operation, expected operational transient (AOO), design basis accident (DBA), core melt design extended condition (DEC), and severe accident.

Initial virtual events assume all cases that reflect the design and operation conditions of the power plant in addition to the list of widely known events.

Examples of specific initial hypothetical events are as follows.

- AOO (decrease in feed water temperature, increase in feed water flow rate, increase in main steam flow rate, turbine trip, etc.)

- DBA (small coolant loss accident, loss of off-site power, rupture of main steam engine, rupture of main water pipe, etc.)

- Core non-melted design expansion conditions (power plant power outage accident, main steam engine rupture + steam generator tube rupture combined accident, steam generator multiple tube rupture, etc.)

Serious accident (large coolant loss accident, main steam engine rupture, power plant power outage → core meltdown)

Next, the accident type of the initial virtual event is determined and an emission path is developed (S300).

The accident types of the initial incident subject to analysis can be classified into process accidents and device damage accidents. For example, types of process accidents include steam pipe rupture (SLB) and main water supply rupture (FLB), and types of equipment damage accidents include waste system failure accidents.

A process accident is an accident in equipment that performs a driven device (a static structure that does not perform a specific function or operation, e.g. piping, tank, etc.), and an equipment damage accident is an accident involving a specific function (solid/liquid/gas waste disposal system, main steam system, etc.). , main water supply system, etc.).

The reason for classifying them as process accidents and equipment damage accidents is because the safety grade classification method for each accident is different.

For process accidents, the initial conditions are set based on normal operation (100% power operation) conditions, and the released dose is calculated using the main factors such as nuclear fuel damage rate, leakage flow rate from the primary side, and vaporization fraction as independent variables. It is assumed that all devices operating under normal conditions operate normally. Therefore, in process accidents, the flow path changes depending on the location of each accident, resulting in a different emission path compared to the normal state.

An equipment damage accident refers to an accident (non-operation) of equipment that performs a specific function (solid/liquid/gaseous waste disposal system, main steam system, main water supply system, etc.) that operates or is required to operate under normal or accident conditions. It is assumed that other than certain functions (e.g. liquid waste treatment system), the remaining functions operate normally. In this case, the emission path is the same, but the initial inventory amount for each nuclide varies compared to the normal state. In addition, device damage incidents are graded according to the frequency with which the function is used, the ending of the function becoming invisible, and the timing and duration of the function's use. In fair accidents, this grade adjustment step does not exist.

Next, radioactive release pathways are developed for each classified accident type. Emission pathways during process accidents include, for example, those to the nuclear reactor building, auxiliary buildings, and steam generators. Paths of device damage accidents include, for example, discharge paths to auxiliary buildings or complex buildings.

The emission path refers to the path along which radioactive materials move when an accident occurs at a specific location (from the inside of the building to the outside, from a high-pressure area to a low-pressure area), and the alienation dose is evaluated at the location where the dose from the radiation source is maximum.

Next, the radiation emission value at the time of functional failure is derived from the collected initial virtual events (S400).

Calculate the degree of radiation emission through the corresponding emission path during an accident, taking into account factors that have a significant impact on the radiation outcome.

As used herein, “functional failure” means that a function required for a nuclear power plant, such as heat removal or reactivity control, does not operate properly.

The degree of radiation emission is calculated through an analysis code (program), and the applied analysis code may differ depending on the location of the radioactive material. The location of radioactive materials may be the reactor core, reactor coolant system (RCS), chemical and volume control system (CVCS), liquid waste disposal system (LRS), and engineered safety facility (ESF) system.

Major factors affecting radioactivity include, but are not limited to, nuclear fuel damage rate (1%, 0.25%, etc.), radioactive nuclides (iodine, cesium, krypton, xenon, etc.), and radioactive material state (gas, liquid, etc.) solid), radioactive material treatment method (low-temperature distillation, low-temperature adsorption, activated carbon filtration, silver nitrate, etc.), waste treatment system or equipment efficiency, etc.

Basically, calculations must be performed according to the accident initial conditions in all power plant states, but if the calculations under several conditions result in a serious or low level result, among the subsequent accident conditions, conditions that are more unfavorable than severe can be considered more favorable than severe or low. With a low condition, decisions can be made without calculation.

The derived radiation emission value is the accident initial condition (Intial Condition) if the power plant status [normal state, expected operational transient (AOO), design basis accident (DBA), design extended condition (DEC), severe accident, shutdown low power] is different. will change, so the calculation must be performed again.

Next, the derived radiation emission value is compared with the standard (S500).

At this stage, the radiation emission calculation results at the time of an accident are compared with the limits and the grade is confirmed.

In this comparison, the severity according to the radiation emission calculation results at the time of an accident is evaluated based on the alienation dose, and an example is shown in Figure 3. The severity is determined by comparing the analysis results performed with various initial conditions as input and the limit values.

Next, the comparison results are listed by function (S600).

Emission levels for each accident are collected and listed by function, and an example of the listing form is shown in Figure 4.

Other examples of functions include heat removal, reactivity control, containment of radioactive materials, and others (monitoring, measurement, control functions, etc.).

Finally, the ending severity for each function is determined (S700). In this step, the incidents that have the greatest impact on the ending severity in each function are determined, and the incidents with the most serious impacts and their grades are identified from the developed list.

The level is not limited to this, but can be divided into serious (safety level 1), normal (safety level 2), low (safety level 3), and minor (non-safety level).

If there are two or more accidents in which a specific function is used, the most serious result is adopted, and the severity is determined by comparing the radiation outcome analysis result (alienation dose) assuming that the specific function does not operate in a specific accident with the limit value.

If the grade of the function determined thereafter significantly deviates from engineering expectations or is at the boundary of the grade, the incident is verified through a separate detailed analysis.

In the present invention described above, a method of determining the severity of radiation consequences is used by setting emission paths for each type of initial virtual event and utilizing variables that have a significant impact on emission, and the reliability and quality of the determined functional level are improved compared to qualitative analysis. In addition, the number of cases requiring detailed analysis is minimized, saving time and effort.

The above-described embodiments are examples for explaining the present invention, and the present invention is not limited thereto. Anyone skilled in the art to which the present invention pertains will be able to implement the present invention by making various modifications thereto, so the scope of technical protection of the present invention should be determined by the appended claims.

Claims (8)

In the method of determining the severity of each function of a nuclear power plant,
The method is performed by a computer,
Establishing a standard for determining the severity of the outcome when a function fails;
collecting initial virtual events of the nuclear power plant;
Deriving radiation emission values upon functional failure from the collected initial virtual events;
comparing the derived radiation emission value with the reference;
It includes the step of listing comparison results by function,
After the above collection,
Further comprising the step of determining the accident type of the initial hypothetical event,
The above accident types include process accidents and equipment damage accidents.
After determining the above accident type,
It further includes the step of deriving a radioactive emission path for each accident type,
In the step of deriving the radiation emission value,
Calculate the degree of radiation emission through the radiation emission path,
In the step of deriving the radiation emission value,
Considering the factors affecting the radiation outcome in the event of the accident,
The derivation of the radiation emission value is performed using an analysis code,
A method wherein the factor includes at least one of nuclear fuel damage rate, radioactive material nuclides, radioactive material status, radioactive material disposal method, and efficiency of waste disposal systems and equipment. delete delete delete delete delete delete According to paragraph 1,
The method further comprising determining a function-specific ending severity from the list.