Waste package degradation expert elicitation panel: input on corrosion of CRM alloy C-22 Page: 4 of 33
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Draft Rev.8 - Joseph C. Farmer, LLNL, YMP WP Degradation, Expert Elicitation Panel, March 30, 1998
Table 1. Suppression ofpH by Hydrolysis Reactions in FeC2, NiC2, and CrCl3 (25 C).
Salt 1 N 3 N Saturated
FeCI2 2.1 0.8 0.2
NiCl2 3.0 2.7 2.7
CrCl3 1.1 -0.3 -1.4
The lowest possible pH values expected with FeC2 solutions at 25*C is 0.2. The pH levels measured in
FeC3 solutions by Francis Wang are shown in Table 2.
Table 2. Suppression of pH by Hydrolysis Reactions in FeCl3 Solutions (25'C).
FeCl3 (wt. %) pH
More realistic estimates must include transport of Fe2+ and other species out of the crevice, limitations on
the rate of Cr transport into the crevice, pH buffer effects due to other ion, and precipitation of
hydrolyzable Fe2+ by carbonate. Such effects will tend to make the pH higher than these extreme values
based upon thermodynamic equilibrium. A transport model for crevice corrosion has been developed by
two of members of this Expert Elicitation Panel and was used to predict a pH of roughly 2.8-3.2 during
the attack of Alloy 625 [J. C. Farmer, R. D. McCright, "Crevice Corrosion and Pitting of High-Level
Waste Containers: Integration of Deterministic and Probabilistic Models," Paper No. 160, Annual
Meeting of the National Association of Corrosion Engineers (NACE), Corrosion 98, San Diego, CA
March 22-27, 1998].
Crevice Corrosion of Alloy 625: E.,i = Epit + 0.1 V
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Figure 1. Prediction of transport-limited pH suppresion in crevice during attack of Alloy 625. The
potential assumed as a boundary condition at the crevice mouth (applied potential) was fixed at a level
100 mV more anodic that the critical pitting potential of Alloy 625.
-+- 600 sec
---- ---3000 sec
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Farmer, J. C.,LLNL. Waste package degradation expert elicitation panel: input on corrosion of CRM alloy C-22, report, March 30, 1998; California. (https://digital.library.unt.edu/ark:/67531/metadc675160/m1/4/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.