Characterization of Bruce Power Unit 6 Preheater Tube Oxide

Abstract

The primary oxide on three sections from Unit 6, Steam Generator 4 Preheater, cold leg side straight length tubing was chemically and radio-chemically characterized. The data were required partially in support of the primary side clean of Unit 5 steam generators in Fall ’05 and partially to enhance our understanding of the characteristics of oxide deposits. The oxide consisted principally (97 wt %) of magnetite; other elements present in the magnetite structure included chromium, nickel, cobalt, copper and titanium. Across the thickness of the oxide layer, the relative levels of chromium and nickel were similar to that present in the base metal. The magnetite loading ranged between 190 and 340 g/m2. Over a tube length of approximately 2.2 m, the thickness of oxide increased from 60 μm near the CO7 support plate to 112 μm near the cold leg tubesheet. Co-60 was the dominant gamma emitting radionuclide present in the preheater oxide. The specific activity of Co-60 generally decreased with oxide thickness as the base metal interface was approached. Non-gamma emitting radionuclides, namely, Fe-55, Ni-63 and transuranics were also quantified. Their scaling factors were generally consistent with those previously obtained from characteristics of steam generator oxides