Development of a novel method for validating severe accident management guidelines (SAMGs) using colored petri nets tool (CPN tool)CPN tool을 이용한 중대사고관리지침서 신검증방법 개발

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An earthquake in 2011 caused the Fukushima nuclear accident in Japan, which had a significant impact on the global nuclear industry, and aroused attention to severe accident management. Severe accident management guidelines (SAMGs), a guideline describing strategies for mitigating severe accidents that melt fuel, should be credible and verifiable to ensure the effectiveness of severe accident management. In addition, unlike for emergency operation procedures, the SAMGs require iteration to achieve their goals, because there are uncertainties in severe accidents, uncertainties in implementation of strategies, and uncertainties in available components. This complicates the implementation paths, making it difficult to validate the workflow of the guidance. As a method for validating severe accident management guidelines, three methods have been used so far: a full scope simulator, a tabletop drill, and a severe accident code. It is impossible to validate all the paths precisely due to the limitations of human capacity, and in particular, the time required for the implementation of the strategy cannot be verified. Therefore, we propose a validation method using a computer that can compensate for such limitations and reflect the time required for strategic implementation. To validate the severe accident management guidelines based on the computer, we needed a computer program that models the workflow of the severe accident management guidelines. There are many programs that can model workflows, such as CPNs (Colored Petri Nets) UML AD (Unified Modeling Language Activity Diagrams) and BPMN (Business Process Management Notation). The CPN tool was chosen because with it, it is easy to construct models and it is able to find workflow errors. To validate by computer, we developed a model that simulates the workflows of the guidelines. The severe accident management guidelines include the Emergency-01 guide used by the operator in the main control room, the Control-01 guide for determining whether to implement the strategies for mitigating accidents, the seven mitigation guidelines for implementing the severe accident mitigation strategies, the Monitoring-01 guide to monitor long-term concerns, and finally the Termination-01 guide to identify termination criteria. The CPN model was developed to integrate and operate all the guidelines, and the developed model was verified to be simulated as the execution path of the SAMGs. Based on the developed CPN model, the items derived for the validation of guidelines are the method using the simulation function of the CPN tool, the method using the State Space Analysis function, and the method using both functions simultaneously. The method using the simulation function 1) simulates and assigns various initial values with a combination of seven variables to simulate various situations at the time of application of the severe accident management guidelines, 2) takes into account the uncertainty of equipment used in the severe accident strategy, and 3) changes the existing order to confirm whether the order of the severe accident mitigation strategy is appropriate. As the CPN model verified that the execution paths of the CPN model and the SAMGs were confirmed to be consistent, the workflows of the SAMGs were indirectly validated by verifying the workflows of the CPN model. The CPN State Space Analysis (SSA) function was used to validate that the execution paths of the guidelines proceeded to the intended path without any blockages, and to find errors in the workflows. State Space Analysis can know the behavior of the model, but if the model is too large or the path includes infinite repetition, the State Space Analysis cannot be performed due to the state explosion problem. In order to solve this problem, the first step analyzed SSA by each guideline model, and when the analysis was completed, the second step performed SSA of the merged model to simplify the model size. The severe accident management guidelines go through the validation process at the time of initial development, but it must go through the validation process even when the guideline is modified after development. Therefore, the validation method to find the errors using the simulation and State Space Analysis function was presented and the validation was performed. In this study, we developed a computer-based new validation method and verified the severe accident management guidelines using the developed CPN model. The results of the validation confirmed that the severe accident management guideline reached the termination criteria for severe accident management even with various initial values, minimum strategic implementation devices, and changes in the order of strategic implementation. Most of the workflow validation using the State Space Analysis function found that the guidelines were appropriate but an error as a duplication of measures was found in the Emergency-01 guidelines. After reviewing the Emergency-01, we found that this error should be reflected. This study confirmed that the proposed new validation method can verify the uncertainty of severe accidents and action time, which cannot be verified by the existing validation method, and can find errors in the complex execution path. The validation of the severe accident management guidelines is expected to improve the capability of responding to severe accident management in power plants. In addition, the developed CPN model is expected to be effective in the training of severe accident management guidelines as it can visually see the progress of the execution paths.
Advisors
Seong, Poong Hyunresearcher성풍현researcher
Description
한국과학기술원 :원자력및양자공학과,
Publisher
한국과학기술원
Issue Date
2020
Identifier
325007
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 원자력및양자공학과, 2020.2,[iv, 86 p. :]

Keywords

Validation of severe accident management guidelines▼aCPN Tool▼aWorkflow▼aState space analysis▼aComputer-assisted validation; 중대사고관리지침서 검증▼aCPN Tool▼a업무흐름도▼a상태공간분석▼a컴퓨터기반 검증

URI
http://hdl.handle.net/10203/283509
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=901974&flag=dissertation
Appears in Collection
NE-Theses_Ph.D.(박사논문)
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