Many boiling water nuclear reactors (BWRs) throughout the world have applied the
NobleChemTM (or noble metal chemical addition: NMCA) process 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
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 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 the
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 process.