Importance of pipes and fittings in the operation of French nuclear power stations: the role of approval policies

A pressurised water reactor, with both its associated nuclear circuits and the conventional part of the power station, requires approximately 15 000 valves, check valves, safety valves and associated actuators. These components, which are of vital importance for the optimum performance of the plant, regulate the flow of fluids, in particular water and pressurised steam. These appliances are sometimes subjected to extreme operating conditions, because of pressure and temperature conditions and also constraints which may result from thermal transients. All these appliances play an active role in ensuring the safety of the reactor and the availability of the plant. In 1996 7 % of outages were linked to valves and fittings. Valves and fittings maintenance represents an annual expenditure of FF 510 m or around FF 9.5 m by plant. With these stakes in mind, and thanks to the EDF test facilities, the author will present the different types of equipment test in both 'normal' and 'accident' conditions, as well as the monitoring of the tests and their evolution following operational feedback from he plant in service. Given the constant evolution of methods used, calculation/computation codes, studies, tests, development and experimental research exist in symbiosis with department using EDF's internal skills, and in collaboration with outside organisations and manufacturers. These studies aim to increase our knowledge with a view to improving this equipment, the technology it uses and maintenance tools and methods. (author)