A method of examining iron oxides speciation and transport to steam generators during nuclear power reactor startups

Secondary side corrosion products (sludge) collected during one of CANDU11 reactor startups from wet layup have been examined by X-ray fluorescence and Mössbauer spectroscopy. The transport and chemical form of iron oxides and oxyhydroxides were determined in condensate, feedwater and preheater outlet as a function of temperature and time. The sludge burst and oxidation states of iron oxides were correlated with the rise of reactor power and corresponding changes in temperature, condensate vacuum and water flow rate. In particular, a sharp γ-FeOOH to Fe3O4 switch was observed that coincided in time with the onset of condensate vacuum. Also, it was found that the startup after wet layup is characterized by only brief and fairly small sludge burst at about 30% reactor power and which contributes only a small amount of undesirable α-Fe2O3 to total iron transport to steam generator. Thus, sludge burden to steam generators can be minimized with proper layup and startup practices.