Electrochemical corrosion potential modeling in the primary heat transport circuit of the Chinshan boiling water reactor under the condition of hydrogen water chemistry with noble metal coating

The technique of noble metal treatment, such as noble metal coating (NMC) or noble metal chemical addition, accompanied by a low level hydrogen water chemistry, is being employed by a number of nuclear power plants around the world for mitigating intergranular stress corrosion cracking in the vessel internals of their boiling water reactors (BWRs). A computer model DEMACE was expanded and employed to assess the effectiveness of NMC throughout the primary heat transport circuit (PHTC) of a BWR. The effectiveness of NMC was justified by the electrochemical corrosion potential (ECP) and crack growth rate (CGR) predictions. In calculating the ECP, enhancing factors for the exchange current densities of redox reactions available from recently published data, were employed. The Chinshan BWR was selected as a model reactor. According to the modeling results, it was found that the effectiveness of NMC in the PHTC of a BWR could vary from region to region at different feedwater hydrogen concentrations. For the selected BWR, NMC was predicted to be of little benefit when the feedwater hydrogen concentration reached 0.9 ppm or over. In particular, the NMC technique proved to be beneficial in reducing ECP and CGR along the PHTC even if the BWR was operated under normal water chemistry. (author)