[en] Degradation of steam generators (SGs) has a significant effect on CANDU heat transport system effectiveness and the overall efficiency of a nuclear power plant. SG degradation results in an increase in the reactor inlet header temperature (RIHT), which has to be kept below an upper limit to avoid dryout of the fuel. Therefore, a better understanding of SG degradation mechanisms is needed to avoid plant de-ratings. In this report, various SG degradation mechanisms are identified and their effect on the RIHT is quantified using field data and numerical modelling. Analysis shows that thermal performance of CANDU SGs has been mostly affected by a combination of divider plate leakage and tube-bundle fouling. The results also indicate that the rate of tube-bundle fouling in CANDU 6 steam generators is equal to 2.05*10^-6 m²·^oC/W per effective full power year (EFPY), of which the majority of this is attributed to primary-side fouling. (author)