This paper presents a prognostic model for sodium-cooled fast reactor (SFR) steam generators (SGs). The purpose of the model is to support the decision making of autonomous control systems based on the reaming useful life estimation. 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 of SG prognostic model development. Understanding its failure mechanisms and determining the degree of degradation are the important elements of prognostics and health management. Based on our literature review and physics-based analysis, we concluded that creep would be a dominant degradation mode of SFR SGs and thus 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 phase 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 and temperature and associated uncertainties through Monte-Carlo methods. Two case studies were presented. The first one demonstrated the model?s capability to calculate the failure probability for a new specimen within a given time. If the tube is working under temperatures of 500C ± 3 and pressures of 15.2 MPa, which leads to LMP of 20100 ± 50, the failure probabilities within 50, 70 and 90 years are approximately 0.1%, 3.2% and 17.5%. The second demonstrated how adjusting the workload can help to protect the integrity of the component. For an old tube reaching 99% of its lifespan, continue to run at temperatures of 500C ± 3 and LMP of 20100 ± 50 leads to a failure probability of about 28.5% within a year. If the temperature is reduced by 5 C, the failure probability can be reduced to 1.2%, and, if the pressure is also reduced such that the LMP is increased by 100, the failure probability can further be reduced to 0.12%.
