People were aware of the risk from the very beginning From the construction of the first Fermi pile in 1942, precautions were taken to ensure reactor safety, with several – albeit rudimentary – means of shutdown, but which inspired the systems in use today. An operator was thus stationed above the pile, armed with an axe, ready to cut the rope which retained an emergency stop bar coated with cadmium, a powerful neutron absorber, which would then drop by gravity into the reactor core. A second operator, also stationed above the pile, held a bucket filled with a cadmium sulphate solution ready to be poured onto the reactor if necessary. The pile was controlled by a hand-operated horizontal cadmium control rod and the neutron flux was monitored by measuring instruments. October 1956, the first incident in France In October 1956 in reactor G1 on the Marcoule site, a fuel cartridge that was incorrectly positioned in its channel heated up and caught fire. Seven kilograms of nuclear fuel melted. Thanks to the cladding failure detection system, the reactor pile stopped, but lacking appropriate handling systems, extraction of the cartridge – which was done virtually by hand – was complicated. This first incident in France remains unknown to the general public. The beginning of regulation of nuclear safety Between 1945 and 1955, the first years of development of nuclear energy in France, there were no specific safety rules other than those that the researchers, engineers and technicians imposed upon themselves. At the end of 1957, Francis Perrin, the High- Commissioner for Atomic Energy in France, initiated a reflection of the organisation of nuclear safety. ••• “Nobody can guarantee that there will never be a serious accident in France. It is therefore necessary to do two things: try to reduce the probability of this happening, and to mitigate the consequences if it does. That, in a nutshell, is the philosophy underpinning nuclear safety.” André-Claude Lacoste ASN Chairman from 2006 to 2012 Nuclear accidents and developments in nuclear safety and radiation protection • 3 Criticality In the field of nuclear engineering, criticality is a discipline which aims to assess and prevent the risks of an unwanted chain reaction in nuclear facilities. It is a sub-discipline of neutronics. The criticality risk is the risk of triggering an uncontrolled fission chain reaction.
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