Assessing Operational Situations.

Abstract

In spite of the high level of automation commonly applied to today’s engineering system, humans’ skill and knowledge still plays a central role in the systems’ daily operation, critical decision making, and accident management. The complexity of the engineered system poses great challenge for human operators to perceive and understand the operational situation. The research domain of situation awareness approaches the operational challenges from the human cognition perspective while the presented thesis aims at supporting situation assessment from the system perspective. The thesis has reviewed different perspectives on situation awareness in the human factor studies and uses the knowledge reflectively for system representation and analysis. The human cognitive activities during complex plant operation and how they perceive a situation and what kind of knowledge has to be established in the human mental model for the operators to be aware of the situations has motivated the utilization of functional representation in system level of situation assessment. The thesis has summarized the MFM syntax and provides detail instructions of how to model by using the modeling technique. A PWR primary system is used as a comprehensive modeling case to demonstrate the MFM modeling procedure. Then the thesis investigates the usability of functional modeling approaches to define and model a plant operational situation. MFM modeling is proposed because it is a formalization combining the means-end and part-whole dimensions of a system, so that the MFM models can therefore represent a complex system at several abstraction levels. MFM models also model cause-effect dependencies of functionalities and objectives of the system in different abstraction levels, so the model can be used for causal reasoning. This thesis extends the causal reasoning methods for MFM models and exploits the ability for MFM models to represent operational knowledge and operational modes. Both concepts are of great importance for situation assessment. By applying the extended MFM theory, situation assessment procedure is developed to assess the plant operational situation. The assessment procedure is demonstrated on the PWR model case