EFFECTS OF HCO 3 - AND SO 4 2- ON THE PITTING CORROSION BEHAVIOR OF Cu

Abstract

As a kind of clean,efficient and relatively safe energy,nuclear energy has been widely used around the world.The high-level radioactive waste generated in the nuclear has also become a major risk,so the disposal safety of high-level radioactive waste will be especially important. The strategy for disposal of high-level radioactive waste in China is to enclose the spent nuclear fuel in sealed metal canisters which are embedded in bentonite clay hundreds meters down in the bed-rock.The choice of container material depends largely on the redox conditions and the aqueous environment of the repository.One of the choices for the fabrication of waste canisters is Cu,because it is thermodynamically stable under the saline,anoxic conditions over the large majority of the container lifetime.For this advantage,some other countries(Canada,Sweden) have selected Cu as the material of nuclear waste container.However,in the early aerobic phase of the geological disposal the corrosion of Cu could take place,and the corrosion behavior of Cu would be influenced by the complex chemical conditions of groundwater markedly.Pitting corrosion of Cu often take place in power plants or air-conditioning condensate water.The corrosion environment usually contains HCO_3~-,SO_4~(2-) and CI~- ions.In the early stage of geological disposal,if the aerobic water with HCO_3~-, SO_4~(2-)and Cl~- immersion repository,the pitting corrosion of Cu may occur.The content of HCO_3~- and SO_4~(2-) in the water chemistry environment,as well as the synergy between them,could affect the behavior of pitting seriously.In this work,the cycle polarization behavior and surface morphology of pitting has been investigated in HCO_3~- and SO_4~(2-) mixed solution,respectively by electrochemical cyclic polarization test and SEM.The results showed that the pitting corrosion behavior of Cu can be divided into the type of active dissolve and the type of film rupture;SO_4~(2-) could increase Cu pitting sensitivity in both of the two types pitting corrosion.Due to synergies with the SO_4~(2-),HCO_3~- could increase the pitting susceptibility first and then reduce the law.In passive film rupture pitting system, SO_4~(2-) could improve the ability of induce pitting;HCO_3~- could reduce the ability of induce pitting. There is no significant impact on pitting self-healing capacity by the two ions.