Sandia's Integrated Risk Management Department has developed a qualitative risk assessment (QRA) process to provide safety analysts with a tool for proper application of the Department of Energy's risk assessment "binning" criteria to non-nuclear facilities. The process provides a framework for performing relatively inexpensive, consistent qualitative assessments, while retaining the best attributes of more costly quantitative methods. It identifies the important contributors to risk and provides a defensible basis for ranking risk and making decisions on risks. It has the additional benefit of enhancing the effectiveness of risk assessment reviews.
The process begins with the development of hazard or accident scenarios, which are separated into logical subelements that involve initiating events, physical structures, systems equipment, and human actions.
The overall likelihood of a scenario is determined by the likelihood of the occurrence of each subelement. Generic failure data that take into account the independence, dependence, and common-cause failure modes are applied to each subelement.
When the elements of an event sequence are properly analyzed, the appropriate likelihood of occurrence and consequence bins can then be assigned. This increases the validity of the risk assessment process, permitting proper management attention. The methodology also includes a risk "acceptability" matrix to aid decision-makers in determining the need for additional risk reduction measures.
Submitted October 1996