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ATTACHMENT B

Methodology for Estimatirg ECP inDresden-2 RWCU Piping

December 1,1992

(Methodology generated by General Electric)

9212150016 921204fDR ADOCK 05000237

PDRztrain2/268/1

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METHODOLOGY FOR ESTIMATING ECP IN DRESDEN - 2 RWCU PIPING

The following is the methodology to be used to estimate the ECP at points ofinterest in the,

RWCU piping at Dresden 2. It should be noted that the RWCU flow comes only from therecirculation water; the bottom head drain is not used.

1. Obtain the ECP values measured in the recirculation flange at various feedwaterhydrogen injection rates.

2. Determine the location of the ECP flange relative to the recirculation piping inlet.

3. Determine the location of the RWCU piping inlet relative to the recirculationpiping inlet.

4. Determine the location of the point of interest for ECP estimation in the RWCUpiping relative to the RWCU piping inlet.

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5. Utilize the information on the locations (Steps 2-4), line lengths, recirculation andRWCU pipe sizes, flow rates and temperatures to calculate the hydrogen peroxideconcentrations at the point ofinterest on the RWCU piping relative to theconcentrations at the electrode locations at several feedwater hydrogenconcentrations which will be determined.

5a. The iW<R water radiolysis model indicates that the predominant oxidizingspecies is hydrogen peroxide at feedwater hydrogen concentrations where theIGSCC protection point is approached in the recirculation system.

5b. I.aboratory data obtained previously [1] and being obtained currently [2] onthe variation of the ECP with increasing hydrogen peroxide concentrationsindicates a substantially more positive ECP than obtained at correspondingoxygen concentrations, especially at lower concentrations.

6. Calculate the extent of hydrogen peroxide decomposition at the point ofinterest onthe RWCU piping relative to that at the recirculation pipe location utilizing aformula which takes into account the effects of flow rate, surface-to-volume ratio,

temperature and mass transfer. The formula includes Sherwood, Reynolds andSchmidt numbers.

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6a. This information is described in a journal article [3) Relevantcalculations are summarized as follows:

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C=Co exp(-k.t) I

k = k k,,/k + k,,m m

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k is calculated from laboratory data shown in Figure A 1 of [3], attached.m

k ,is calculated from the following equations:

k,, = KS/V

Sh = Kd/D

Re = dU/v

Sc = v/D

K = 0.023Re semD/du

where:

C = H 0 concentration at time t22

C, = Initial H 0 concentration at time t = 02 2

t = reaction timek = observed hydrogen peroxide decomposition rate constantk = rate constant from chemical activationm

k , = rate constant from diffusionSh = Sherwood numberRe = Reynolds numberSc = Schmidt numberd = pipinginner diameterD = diffusivity of H 02 2U = water flow velocityv = kinematic viscosity

(S/V) = surface to volume ratio

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6b. The basic values for the decomposition rate constants were obtained inlaboratory studies [1], [2]. Data from [2] is shown graphically in Figure 1,attached.

7. For the previously determined feedwater hydrogen concentrations, compare thehydrogen peroxide concentrations at the point ofinterest on the RWCU pipingrelative to the electrode location. Using the information in 6b estimate the ECP atthe point ofinterest on the RWCU piping compared with the electrode location.

References

1. C. C. Lin, et al, " Electrochemical Potential Measurements Under Simulated BWRWater Chemistry Conditions," Corrosion, Vol. 48, No.1, January 1992

2. Y. Kim, et al, Effect of Water Flow Velocity on Electrochemical CorrosionPotential of Stainless Steel in 288+C Water," National Association of Corrosion

Engineers, to be published in 1993.

3. C. C. Lin, et. al., " Decomposition of Hydrogen Peroxide in Aqueous Solutions atElevated Temperatures", Int. Journal of Chem. Kinetics, Vol. 23,971-978 (1991).

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Effects of H 0 on the ECP of 304 SS in High Purity Water at 270 C.2 2Average of Several Measuresnents Using Ag/AgC1, Cu/Cu2O and Pt Reference Electrodes.

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