Multi-state top event prevention analysis

Abstract

Choosing the set of systems, structures, and components (SSCs) for achieving the necessary performance to meet the safety objectives of a hazardous fecilily constitutes a type of "selection problem,"since all the selected elements must work together toward that goal. It is important that such objectives be accomplished as efficiently as possible. Top Event Prevention Analysis (TEPA) is a systematic tool for solving this selection problem by, in effect, deciding where to best allocate resources to ensure SSC performance. Inputs to TEPA include risk model cut sets, and its output is a list of prevention sets, each of which is a selection of elements whose joint reliability performance (achieved through prevention of failures) satisfies the safety objectives. In most existing applications of TEPA, basic events either do or do not fall within a given prevention set The present paper, based on unpublished work by Youngblood et al, goes beyond that by illustrating TEPA's ability to allocate performance in a more nuanced way than an all-or-nothing approach. For example, with problems set up using multi-state logic rather than binary true/false logic, TEPA can be used to allocate intermediate levels of seismic capacity that efficiently satisfy safety objectives in a practical manner.