The MDTA-based method for assessing diagnosis failures and their risk impacts in nuclear power plants

In the emergency situations of nuclear power plants (NPPs), a diagnosis of the occurring events along an accident progression or as initiating events is crucial for managing or controlling a plant to a safe and stable condition. If the operators fail to diagnose the occurring event(s), their responses to a given event can eventually become inappropriate or inadequate. This paper presents an analytical method for assessing the potential for a diagnosis failure (or misdiagnosis) and its consequences for human behaviour and plant safety. The method largely comprises of three steps as follows: (1) Analysis of the potential for a diagnosis failure, (2) Identification of the human failure events (HFEs) that might be induced due to a diagnosis failure, and (3) Quantification of the HFEs and their modeling into a PSA model. The paper also presents a pilot application of the proposed method to the small loss of coolant accident of a Korean NPP.