An attempt for qualification in nuclear industry: the specific instance of the qualification of valves under accidental conditions of operation

A nuclear French plant of the pressurized water type requires about 12,000 valves in order to monitor the internal flow of fluids (essentially water and vapor). The pressure range can reach and even exceed 150 bar, with diameters ranging between 8 mm and 1 m, and eventually more than that. This wide variety of conditions unveils two major questions for the designer and user to worry with: - to hold the reactor in a state that will not entail unacceptable consequences for the inhabitants in any kind of event, - to avoid as much as possible non intentional shutdowns, which are quite costly for an industrial plant of that size. In order to comply with these two problems, and particularly for the fitting of valves, a high reliability is required for running the equipment. This reliability follows from a global procedure with regard to the main objective at every step: - design: importance of the technical specifications and of the coding process used (RCCM); - manufacture: monitoring plays an essential part at this stage; - starting procedures of the equipment (without or with fluid circulation); - maintenance and recurrent testing procedures; - sampling and accounting for feed back informations and to be sure, laboratory testing for qualification, which should encompass the whole field of operation including even the so-called accidental conditions. This last point is dealt with in the following paper