Nuclear power plants: Using PSA to enhance operational safety

Developed as a logical extension of the old engineering discipline of reliability analysis, probabilistic safety assessment (PSA) was introduced in the commercial nuclear power field in the mid-1970s. To date, more than 70 PSAs have been carried out worldwide for nuclear power plants. The studies provide safety insights that could not have been obtained by other means. In most countries with nuclear power programmes, PSA has become a standard tool for safety evaluations. Briefly stated, PSA is a systematic method of modelling a plant's response to a set of initiating events that could threaten its safe operation. To develop the necessary models, detailed information regarding the plant's design and operation is needed. Basic models (such as fault or event trees) are developed to identify the success and failure paths. In analysing these models, a number of factors are taken into account, including the random failures of components, failures arising from a common cause, human errors, and test and operational strategies. Some PSAs have been initiated by electric power utilities in response to regulatory concerns or to demonstrate low public risks associated with nuclear power plant operations (e.g., at the Zion nuclear plant in the United States, and the Sizewell plant in the United Kingdom). Other PSAs have been sponsored by regulatory bodies to promote and develop the use of the techniques. Moreover, as the methodology has matured, PSA results have been increasingly used for improving the operational safety of nuclear plants.