As the nuclear programmes in OECD countries have matured over the four decades of commercial nuclear power operation, this maturation has brought steady improvements in the operational safety of nuclear power plants. This improvement is demonstrated by several performance indicators, but most notably by the reduced frequency and severity of accident precursor events relative to the events of, say, ten to twenty years ago. One of the major reasons for this improved performance has been the extensive use of lessons from operating experience to backfit safety systems, improve operator training and emergency procedures, and to focus more attention on human factors, safety culture and nuclear quality management systems. Indeed, a prominent lesson from the TMI-2 accident in 1979 was the need for systematic evaluation of operating experience on an industry-wide basis, both by the nuclear industry, which has the greatest direct stake in safe operations, and by the nuclear regulator...