Safety and safety analysis. From CP1 to Fukushima

The safety of nuclear installations has been a serious concern starting from the days of infancy of this technology. When Fermi and co-workers built the first nuclear reactor in 1941, the Chicago Pile-1 or CP1 at the University of Chicago, some basic safety principles still in use today were already part of this very simple experiment. During the fast-growth period in the 1960ies, a number of NPP systems were conceived, tested and some of them built, mainly in the US and in the Soviet Union, but also in the UK, in France and in Canada, before just a handful of nuclear systems dominated: the LWRs conquered some 3 quarters of the world market and their dominance continues till today. The fission process has been amazingly well ''designed'' by nature: a remarkably simple to produce, self-sustained reaction that can be easily controlled, modulated and adjusted by a variety of available materials. Fission leads to large release of energy that can be easily collected and transformed into useful work. The process has only a major drawback, the inexorable production and accumulation in the core of the radioactive fission products that also produce decay heat. Criticality considerations put apart, the major goal of reactor safety is the confinement and cooling of these fission products. Although safety has been a major concern from the very first nuclear developments, feedback and actions following incidents and accidents have contributed to continuous enhancements. In particular, the three major nuclear accidents, TMI, Chernobyl and Fukushima had or will hopefully have in the future major impacts on safety improvements. Lessons learned from TMI have greatly enhanced the safety of LWRs, while Chernobyl triggered a number of radio-ecology studies and improved the readiness for radiological crisis management. It is hoped that Fukushima will be the trigger for much stronger international oversight and harmonization of safety practices, something that has already been launched, in particular by the IAEA conventions but has lacked until now true enforcement power. (orig.)