What we now know (and don't know) about reactor safety

This paper deals with the likelihood and consequences of major reactor accidents. Our understanding has advanced markedly in the past decade, largely because of the use of probabilistic risk assessment. There is now a good understanding of accident sequences, despite some important gaps. The insights achieved have in many ways revolutionized the reactor safety community's view of the relative importance of various safety issues. Understanding of severe accident phenomena is still inadequate, but experiments and development of analytical methods will soon enable us to calculate better the phenomena involved in core degradation, core melting, containment behavior, and the ultimate fate of fission products released from a melted core. Also, we are now gaining important insights into analysis of human errors and external initiating events. Thus the next decade will see another quantum jump in our understanding, rivaling the progress of the last decade.