Criticality: To simulate in order to prevent accidents

As a criticality accident is a very dangerous one, articles propose an overview of research and simulation activities which are performed to analyse these situations. While recalling the principle of a chain reaction, and the three different levels of criticality, a first article outlines that the presence of water is an aggravating factor when handling fissile materials such as uranium 235 or plutonium, outlines the interest of modelling equipment behaviour, evokes the existence of CEA experimental installations which are representatives of actual situations, and also evokes works performed in collaboration with the USA. It indicates the validation process for computation codes. A second article describes how safety rules evolve under the influence of analysis of accidents and research programmes: incidents or accidents are identified and reported, the understanding of the accident allows a better intervention organisation, and highly constrained operations are re-examined. A third article briefly describes Areva's modelling activities related to the design of containers and packages used for the transport and storage of spent fuels