Studies of iron redox states, corrosion potentials and oxygen reduction in a simulated feedwater tra...
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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
General background oxygen reduction in a simulated feedwater train

  • 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


Goals of the present work
Goals of the present work oxygen reduction in a simulated feedwater train

  • Study the effect of

  • Interruption of N2H4 dosage

  • Reduced N2H4 addition

  • Reduced temperature in the high pressure heater (HPH)

  • An alternative N2H4 injection point


Experimental loop
Experimental loop oxygen reduction in a simulated feedwater train

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)


Experimental loop1
Experimental loop oxygen reduction in a simulated feedwater train

Base-line chemistry:

100 ppb N2H4

+

8 ppm NH3

+

10 ppb O2

+

5 ppb Fe


Results from previous work
Results from previous work oxygen reduction in a simulated feedwater train

  • 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


Interruption of n 2 h 4 dosage
Interruption of N oxygen reduction in a simulated feedwater train2H4 dosage


Interruption of n 2 h 4 dosage1
Interruption of N oxygen reduction in a simulated feedwater train2H4 dosage


Interruption of n 2 h 4 dosage2
Interruption of N oxygen reduction in a simulated feedwater train2H4 dosage


Reduced n 2 h 4 addition
Reduced N oxygen reduction in a simulated feedwater train2H4 addition


Reduced n 2 h 4 addition1
Reduced N oxygen reduction in a simulated feedwater train2H4 addition


Reduced temperature in hph
Reduced temperature in HPH oxygen reduction in a simulated feedwater train


Alternative n 2 h 4 injection point
Alternative N oxygen reduction in a simulated feedwater train2H4 injection point


Alternative n 2 h 4 injection point1
Alternative N oxygen reduction in a simulated feedwater train2H4 injection point


Alternative n 2 h 4 injection point2
Alternative N oxygen reduction in a simulated feedwater train2H4 injection point


Alternative n 2 h 4 injection point3
Alternative N oxygen reduction in a simulated feedwater train2H4 injection point


General trend
General trend oxygen reduction in a simulated feedwater train


Memory effect
Memory effect oxygen reduction in a simulated feedwater train


Calculated o 2 concentration
Calculated O oxygen reduction in a simulated feedwater train2 concentration


Conclusions
Conclusions oxygen reduction in a simulated feedwater train

  • 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


Conclusions1
Conclusions oxygen reduction in a simulated feedwater train

  • 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


Acknowledgements
Acknowledgements oxygen reduction in a simulated feedwater train

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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