Prognostic model and failure mechanisms of steam generators in Sodium-Cooled fast reactors

•Steam generators (SG) in SFRs are operated at higher temperatures and higher pressure margins than the LWR counterparts.•Other failures, e.g. fatigue, stress corrosive crack, fretting, etc., are far less likely than creep during normal operation.•Creep dominates SFR SG degradationsgiven the high temperature and can be described by Larson-Miller parameter (LMP).•The proposed prognostic model estimates the failure probabilities by sampling LMR and temperature and their uncertainties using Monte-Carlo methods.•The model successfully predicts the failure probability within a given time and suggests how adjusting the workload can protect the component. This paper presents a prognostic model for sodium-cooled fast reactor (SFR) steam generators (SGs). The purpose of the model is to estimate the remaining useful life of SFR SGs and thus to support the decision-making of autonomous control. SFR SGs are of great interest for plant integrity due to their harsh operation environment. They operate at higher temperatures and higher coolant-to-steam pressure differences than those of current light water reactors (LWR). The severity of the SFR SG failure consequences, which include water-sodium contact, is another reason. Understanding its failure mechanisms is important for the development of its prognostic model. Based on our literature review and physics-based analysis, we concluded that creep would be a dominant degradation mode of SFR SGs due to SFR’s high-temperature and high-pressure environment. Thus, creep is the focus of the prognostic model. Various other failure modes were also investigated in this study. The mechanical fatigue due to flow-induced vibration is usually observed in early developmental phases and would not be an important issue during normal operation. The thermal fatigue due to thermal stripping is occasionally observed in other components in SFRs but does not affect SG integrity. Pure water stress corrosive crack, fretting, and so on are commonly observed in LWR SGs but are significantly less important in SFR SGs because of the high temperatures, high pressure differences, and chemical properties of liquid sodium. Based on these investigations, a prognostic model focusing on creep failures was developed. It estimates the failure probability profile by sampling the Larson-Miller parameter (LMP) and temperature and associated uncertainties through Monte Carlo methods. Two case studies were presented. The first one demonstrated the model’s capab