Insights into the formation mechanism of hard sludge on the secondary side of PWR steam generators

In the secondary circuit of nuclear Pressurized Water Reactors, corrosion products and impurities lead to formation undesirable hard deposits, called sludge, on tube sheet steam generators. Theses deposits are mainly composed iron (magnetite), alumina silica. The sludge piles is investigated by reproducing reaction precursor oxides in conditions generator (275 °C, 58 bar). Mixtures magnetite, γ-alumina amorphous silica binary or ternary systems an alkaline ethanolamine-ammonia solution at pH25°C = 9.6 studied. Carbon steel was tested as alternative source iron. analysis evolution suspensions, completed industrial feedback, allows explain process following sequence proposed: sedimentation magnetite/confinement interstitial fluid/concentration aqueous species such alumina/sorption Al magnetite and/or growth boehmite/reaction with form kaolinite a resistant cement. Once formed, cement tends densify over time while passive. absence Fe-phyllosilicates predicted thermodynamics explained low solubility making unfavorable precipitation Fe-silicate. By contrast, metallic not stable contact water continual production divalent iron, whose much higher than that overpass threshold concentration what makes possible berthierine layer surface corroded steel. This constitutes nucleation site for further other aluminosilicates.