Effect of variations in noble metal chemical addition process on electrochemical catalytic response in high temperature water

The NobleChemTM (or noble metal chemical addition: NMCA) process has been applied to many boiling water nuclear reactors (BWRs) throughout the world just before end-of-cycle shutdown or during a mid-cycle shutdown to mitigate the stress corrosion cracking (SCC) of structural materials in BWRs. The first Online NMCA (OLNC) plant demonstration was also successfully completed during the summer of 2005 while the reactor was in power operation. When injected into BWR environments, the noble metal particles deposit on Type 304 stainless steel (SS) surfaces and reduce the corrosion potential, which decreases the propensity for SCC. Very fine noble metal particles are formed and able to potentially deposit inside a crack and maintain catalytic surfaces in the critical regions inside the crack. This paper discusses the effect of various environmental factors that control the size and distribution of noble metal particles on the surface during injection of the noble metal salts, and highlight the benefits associated with the Online NMCA (OLNC) process. (author)