ON LINE FATIGUEMETER - A LARGE EXPERIMENT IN FRENCH NUCLEAR-PLANTS

During operation of PWR plants, thermal transients occur and induce fatigue stresses at critical locations in the nuclear steam supply system. Assessment of cumulative usage factor at these locations is one the major concerns regarding plant life extension. A system based on real time fatigue monitoring his been developed by EDF. The principle of the system, that records plant operating parameters and calculate thermohydraulic conditions, local stresses and usage factor resulting from each individual transient, is firstly presented. Demonstration experiments, concerning two highly stressed locations of reactor coolant system (charging line nozzle and surge line), carried out in two 900 MW units are then described. Finally, analysis of these experiment results is commented. The system allows automatic transients book keeping and usage factor assessment. EDF intends to equip all its PWR units with such fatigue monitoring systems.