Synergy Effect of Simultaneous Zinc and Nickel Addition on Cobalt Deposition onto Stainless Steel in Oxygenated High Temperature Water

Abstract

Effect of zinc and/or nickel addition on cobalt deposition was studied under simulated normal water chemistry condition of boiling water reactor. Type 316L stainless steel coupon was exposed to high temperature water including cobalt ion, together with zinc and/or nickel ions up to 1,000 h using experimental recirculating loops. Either addition of zinc or nickel ions reduced amounts of cobalt deposition on stainless steel. Simultaneous addition of both zinc and nickel ions showed the synergy effect; less amounts of cobalt deposition were observed for simultaneous addition of zinc and nickel ions comparing to individual addition at equivalent concentration. Glow discharge spectrometry and conversion electron Mössbauer spectroscopy revealed that the different mechanism of reducing cobalt deposition prevails between zinc and nickel ions.

A Mixed-Conduction Model for the Oxidation of Stainless Steel in a High-Temperature Electrolyte

“…1,2 It is hence known that the oxide films formed on stainless steels and nickel-based alloys in high-temperature water have basically the same main structure and that the important compounds ensuring the protective character of the oxide film ͑nickel ferrite and nickel and iron chromites͒ are essentially the same for all the nickel-based materials and stainless steels. [3][4][5][6][7][8][9][10][11][12][13][14][15] In addition to the increased understanding of growth and restructuring of oxide films, recent development of radiolysis codes allows the modeling of the chemistry resulting from the radiolysis in virtually any location where the coolant is in contact with any material in light water reactors. The modeling provides the concentration of all radiolysis products, including radicals, and also calculates the local electrochemical corrosion potential in each location, hence providing the basis for determining or establishing thermodynamic, kinetic, and electrokinetic phenomena.…”

In situmeasurement of corrosion of type 316L stainless steel in 553 K pure water via the electrical resistance of a thin wire

“…Hydrogen is the reducing agent to dissolve the protective oxide film and that might enhance the corrosion. The results of corrosion depth measurements in pure water at 553 K under the NWC condition for 118 h (Run 2) are shown in Figure 8 along with literature data and the experimental conditions at which they were obtained [8][9][10]12,27]. Measured ECP of the NWC condition (NWC 1) was þ0.15 V vs. SHE.…”

“…The corrosion depth of 316L SS in 553 K pure water has been reported to be of the order of a micrometre or less [8][9][10][11][12]. The corrosion depths of 316L SS wire specimens (diameter 50 mm) were evaluated using electrical resistance measurements applying a constant current (I) and measuring the potential drop (V) intermittently to obtain the resistance (R) via Ohm's law (Equation (1)).…”

“…Corrosion of stainless steel in pure water at 553 K is thought to be controlled by a parabolic rate law or a logarithmic rate law described as Equation (19) or Equation (20), respectively [7,9]. Consequently, the corrosion depth data were fitted with the equations:…”

“…Other reports have expressed total corrosion rate of 316L SS in oxygenated water at 553-563 K as depending upon time raised to the 2/3 power [8] or being controlled by a logarithmic rate law [9]. Corrosion depths at an early time of 200 h are about 50-80% of those at 1000 h [9,10]. So, corrosion rate at time less than 200 h is important for knowing the corrosion kinetics.…”