EFFECTS OF SURFACE CHROMIUM DEPLETION ON LOCALIZED CORROSION OF ALLOY-825 AS A HIGH-LEVEL NUCLEAR WASTE CONTAINER MATERIAL

Effects of the chromium-depleted, mill-finished surface on the localiz ed corrosion resistance of alloy 825 (UNS N08825) were investigated. T ests were conducted in solutions based on the ground water at Yucca Mo untain, Nevada, but with a higher concentration of chloride (Cl-). Res ults indicated that breakdown (E(p)) and repassivation (E(rp)) potenti als for mill-finished surfaces were more active than those for polishe d surfaces. Potentiodynamic polarization tests indicated pits could be initiated on the chromium-depleted surface at potentials of 220 mV(SC E) in a solution containing 1,000 ppm Cl- at 95 degrees C. Potentiosta tic tests identified a similar pit initiation potential for the mill-f inished surface, However, under longterm potentiostatic tests, a highe r potential of 300 mV(SCE) was needed to sustain stable pit growth bey ond the chromium-depleted layer. An increase in surface roughness also was observed to decrease localized corrosion resistance of the materi al.