The localized corrosion resistance and mechanical properties of alloy 22 waste package outer containers

Abstract

The proposed waste packages for the disposal of high-level radioactive waste at the potential repository at Yucca Mountain, Nevada, consist of an outer container and inner container. The outer container is made of alloy 22, a corrosion-resistant Ni-Cr-Mo-W alloy, while the inner container is made of type 316 nuclear-grade stainless steel. Fabrication processes such as welding and postweld heat treatments can induce changes to the microstructure of alloy 22. Such microstructural changes can reduce ductility and impact strength and promote localized corrosion. Environmental conditions within the emplacement drifts, such as composition of solutions contacting the waste packages, can also affect localized corrosion susceptibility. In this study, the effects of fabrication processes on impact strength, fracture toughness, and crevice-corrosion resistance of alloy 22 were investigated.

Repassivation Potential of Alloy 22 in Sodium and Calcium Chloride Brines

“…Similar findings have been reported before. [8][9][10][16][17][18][19][20][21][22][23] Crevice Repassivation Potential Figure 5 shows the crevice repassivation potential (ERCO) of Alloy 22 as a function of the temperature in NaCl and CaCl 2 rich electrolytes (Electrolytes 5 and 6) for solutions with R = 0.1. For both solutions the ERCO decreased as the temperature increased, and, at each temperature the ERCO was lower in the CaCl 2 rich solution than in the NaCl rich solution.…”

“…[8][9][10][13][14][15] The presence of nitrate ) in the solution minimizes or eliminates the susceptibility of Alloy 22 to crevice corrosion. [8][9][10][16][17][18][19][20][21][22][23] The value of the ratio R = [NO 3 -]/ [Cl -] has a strong effect of the susceptibility of Alloy 22 to crevice corrosion. [16][17][18][19][20][21][22][23][24][25] The higher the nitrate to chloride ratio R, the stronger is the inhibition by nitrate.…”

“…Other anions in solution were also reported to inhibit crevice corrosion in Alloy 22. [19][20][26][27][28] The objective of this work was to examine the susceptibility of Alloy 22 in several electrolyte solutions containing sodium chloride (NaCl), calcium chloride (CaCl 2 ) and sodium nitrate (NaNO 3 ) using the cyclic potentiodynamic polarization (CPP) technique. 29 Ratios R of nitrate over chloride from 0.0086 to 0.25 were investigated.…”

Crevice Repassivation Potential of Alloy 22 in High-Nitrate Dust Deliquescence Type Environments

“…[8][9][10][13][14][15] The presence of nitrate (NO 3 -) and other oxyanions in the solution minimizes or eliminates the susceptibility of Alloy 22 to crevice corrosion. [8][9][10][16][17][18][19][20][21][22][23] The value of the ratio R (R = [NO 3 -]/([Cl -]) has a strong effect of the susceptibility of Alloy 22 to crevice corrosion. [16][17][18][19][20][21][22][23] The higher the nitrate to chloride ratio the stronger the inhibition by nitrate.…”

“…[8][9][10][16][17][18][19][20][21][22][23] The value of the ratio R (R = [NO 3 -]/([Cl -]) has a strong effect of the susceptibility of Alloy 22 to crevice corrosion. [16][17][18][19][20][21][22][23] The higher the nitrate to chloride ratio the stronger the inhibition by nitrate. Most of the work on the susceptibility of Alloy 22 to crevice corrosion was at temperatures of 100°C and below.…”