The operational assessment of steam generator tubes based on a stochastic crack growth model

Abstract

In pressurized water reactor plants, the degradation of steam generator tubes has been one of the main economic and safety problems. Steam generator tubes are subjected to the degradation mechanism of stress corrosion cracking, in which an unstable crack growth may lead to their structural failure. In general, deterministic criteria provide the least conservative assessment in order to plug or sleeve the cracked tubes. As the crack growth rate under stress corrosion cracking is of high random nature, the structural integrity assessment of steam generator tubes must be performed taking into account the failure probability at current and next inspections. In this paper, a stochastic model is applied for performing the operational assessment of steam generator tubes for any time interval. The results obtained with this model are compared with others, such as Monte-Carlo simulation and non-evolutionary statistical model. The proposed methodology is able to provide efficiently a less conservative failure probability. The plausibility of stochastic models in the structural integrity assessment of steam generator tubes is reached in favor of their operational life extension.