Design and Operation of Industrial Assemblies Presenting Criticality Hazards: Experience with French Installations

The operation of various French installations using fissile materials has enabled us to work out a number of rules for dealing with criticality hazards. In this connection it is useful to distinguish two stages in the study of the nuclear safety of an installation, viz. the design stage and the operational stage. In the design stage it is emphasized that the safety studies should be carried out in conjunction with the design work on the installation from the very outset ; project directors should therefore always be kept informed of the latest available data on criticality problems. It is also important to decide as soon as possible what type of control system (concentration, mass, geometry) to use in particular sections of the installation. The various sections of an installation being interdependent, one can in this way devise an over-all solution to the safety problem by locating the controls at the most suitable points. When deciding what type of control system to use, it is essential to aim at the highest possible degree of inherent safety and, particularly where solutions are involved, to make the maximum use of favourable geometries, to the extent that economic considerations permit. In the operational stage, the important thing is to work out and distribute instructions for dealing with the problem of criticality. These instructions should provide clear information on the method of control adopted, the limitations imposed and the procedures to be used for ensuring the latter. To make sure that the instructions are properly understood and applied, operating staff should be briefed on the implications of the criticality hazard and the methods to be used for averting the dangers involved. (author)