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

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 Mossbauer spectroscopy revealed that the different mechanism of reducing cobalt deposition prevails between zinc and nickel ions.