QRAS - the Quantitative Risk Assessment System

This paper presents an overview of version 1.6 of QRAS, the Quantitative Risk Assessment System. QRAS is a PC-based software tool for conducting probabilistic risk assessments (PRA), which was developed to address needs held by NASA, but can be used in a wide range of industries. The software is different from other PRA tools in three key areas. First, QRAS bridges communication and skill gaps between managers, engineers, and risk analysts by using representations of the risk model and analysis results that are easy to comprehend by each of those groups. For that purpose, event sequence diagrams (ESD) are used as a replacement for event trees (ET) to model scenarios, and the quantification of events is possible through a set of quantification models familiar to engineers. In addition, QRAS' graphical user interface provides a more structured guidance than other tools in order to facilitate its use by nonexpert users. Second, QRAS includes a strong support for modeling approaches not typically found in tools developed for the nuclear industry, such as phased-mission modeling. Finally, QRAS applies leading edge reduced ordered binary decision diagram (ROBDD) technology for the accurate and efficient computation of risk results.