Response Of Safety Systems Research Articles

Light water reactor sequence timing: its significance to probabilistic safety assessment modeling

Abstract This paper examines event sequence timing in light water reactor plants from the viewpoint of probabilistic safety assessment (PSA). The analytical basis for the ideas presented here come primarily from the authors' work in support of more than 20 PSA studies over the past several years. Timing effects are important for establishing success criteria for support and safety system response and for identifying the time available for operator recovery actions. The principal results of this paper are as follows: 1. 1. Analysis of event sequence timing is necessary for meaningful probabilistic safety assessment—both the success criteria for systems performance and the probability of recovery are tightly linked to sequence timing. 2. 2. Simple engineering analyses based on first principles are often sufficient to provide adequate resolution of the time available for recovery of PSA scenarios. Only those parameters that influence sequence timing and its variability and uncertainty need be examined. 3. 3. Time available for recovery is the basic criterion for evaluation of human performance, whether time is an explicit parameter of the operator actions analysis or not.