ONLINE FATIGUE MONITORING AND PROBABILISTIC ASSESSMENT OF MARGINS

An on-line computer-aided system has been developed by Electricite de France, the French utility, for fatigue monitoring of critical locatio ns in the nuclear steam supply system. This tool, called a fatigue met er, includes as input data plant parameters and is based on some conse rvative assumptions at several steps of the damage assessment (thermal boundary conditions, stress computation,...). In this paper we presen t recent developments performed towards a better assessment of margins involved in the complete analysis. The methodology is illustrated wit h an example showing the influence of uncertainty in plant parameters on the final stress computed at a pressurized water reactor 900 MW uni t pressurizer surge line nozzle. A second example is shown to illustra te the possibility of defining some transient archetypes.