Example application of model-based HRA approach

In response to a Staff Requirements Memorandum (SRM) to the Advisory Committee on Reactor Safeguards (ACRS), the US Nuclear Regulatory Commission (NRC) has undertaken a research effort to create a consensus approach to human reliability analysis (HRA). The qualitative part of the approach includes a scenario-driven method of capturing possible interactions of the operating crew with the plant. At its top-layer, the method includes a Crew Response Tree (CRT) that identifies human failure events (HFEs). The potential failure mechanisms of the HFEs are explored with the aid of a mid-layer "causal model" using the Information-Diagnosis/Decision-Action (IDA) model and cognitive models from the psychological literature. The last layer of the model links relevant performance shaping factors (PSFs) to each failure mechanism. These layers together embody the results of task analysis and evaluation of context factors performed by an interdisciplinary team of analysts. In each scenario of the CRT, the mid-layer and bottom-layer models are linked together to produce the sequence of events and their causes that lead to one or several HFEs. Two companion papers in this conference proceedings describe the overall methodology and the development of the mid-layer models. This paper presents an illustrative application of the method.