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General background

Studies of iron redox states, corrosion potentials and oxygen reduction in a simulated feedwater train Stefan Forsberg , Studsvik Nuclear AB , Sweden Jerzy A. Sawicki , AECL , Canada Per-Olof Andersson , Ringhals AB , Sweden Anders Molander , Studsvik Nuclear AB , Sweden.

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General background

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  1. Studies of iron redox states, corrosion potentials and oxygen reduction in a simulated feedwater train • Stefan Forsberg,Studsvik Nuclear AB, Sweden • Jerzy A. Sawicki,AECL, Canada • Per-Olof Andersson,Ringhals AB, Sweden • Anders Molander,Studsvik Nuclear AB, Sweden

  2. General background • Corrosion products are transported with feedwater (FW) to steam generator (SG) • Oxidized (due to air inleakage in condenser) • N2H4 added to FW in order to: • Obtain reducing conditions in SG • Reduce oxidized corrosion products (-Fe2O3, -FeOOH, -FeOOH reduced to Fe3O4) • Obtain an alkaline pH

  3. Goals of the present work • Study the effect of • Interruption of N2H4 dosage • Reduced N2H4 addition • Reduced temperature in the high pressure heater (HPH) • An alternative N2H4 injection point

  4. Experimental loop Loop constructed for plant simulation - Materials - Temperatures - Residence times - Fe oxides from electrolytic crud generator Studies of - Potentials - Oxygen consumption - Distribution of Fe species (Mössbauer at AECL)

  5. Experimental loop Base-line chemistry: 100 ppb N2H4 + 8 ppm NH3 + 10 ppb O2 + 5 ppb Fe

  6. Results from previous work • General trends observed (fraction of Fe3O4, potentials, O2 consumption) are consistent with plant data • At the base-line chemistry, the fraction of Fe3O4 was high at pos.1, decreased in the LPH and increased in HPH • At an increased level of O2 (50 ppb) or N2H4 (200 ppb), no large change in Fe3O4 fraction was observed in final FW • O2 is efficiently removed in HPH in the presence of N2H4

  7. Interruption of N2H4 dosage

  8. Interruption of N2H4 dosage

  9. Interruption of N2H4 dosage

  10. Reduced N2H4 addition

  11. Reduced N2H4 addition

  12. Reduced temperature in HPH

  13. Alternative N2H4 injection point

  14. Alternative N2H4 injection point

  15. Alternative N2H4 injection point

  16. Alternative N2H4 injection point

  17. General trend

  18. Memory effect

  19. Calculated O2 concentration

  20. Conclusions • When interrupting the N2H4 dosage, there is a clear memory effect in potentials, O2 concentration and fraction of F3O4 in the final FW • The optimal N2H4 concentration, without significant potential and O2 concentration increase in the final FW, is around 5 to 7 times the inlet O2 concentration • When the temperature of the HPH is decreased from 220oC to 175oC at the base-line chemistry, the O2 concentration in the final FW increases from below 1 ppb to about 2 ppb

  21. Conclusions • When moving the N2H4 injection point forward, the potentials and O2 concentration in the final FW are not changed • When moving the injection point, the fraction of Fe2O3 increases both after the LPH and in the final FW

  22. Acknowledgements This work was funded by Ringhals AB, AECL and Studsvik Nuclear AB Katarina Pein participated in early phase of the project

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