Stress corrosion cracking (SCC), especially in existing boiling water reactor (BWR) components, is most effectively accomplished by reducing the corrosion potential. This was successfully demonstrated by adding hydrogen to BWR water, which reduced oxidant concentration and corrosion potential by recombining with the radiolytically formed oxygen and hydrogen peroxide. However, reduction in the corrosion potential for some vessel internals is difficult, and others require high hydrogen addition rates, which results in an increase in the main steam radiation level from volatile N. Noble metal electrocatalysis provides a unique opportunity to efficiently achieve a dramatic reduction in corrosion potential and SCC in BWRS, by catalytically reacting all oxidants that difise to a (catalytic) metal surface with hydrogen. There are many techniques for creating catalytic surfaces, including alloying with noble metals or applying noble metal alloy powders to existing BWR components by thermal spraying or weld cladding. Most techniques have been targeted at producing catalytic benefits in specific areas. A novel system-wide approach for producing catalytic surfaces on all wetted
components has been developed which employs the reactor coolant water as the medium of transport. This approach is termed in-situ ‘‘noble metal chemical addition” (NMCA), and has been successfully used in extensive laboratory tests to coat a wide range of pre-oxidized structural materials. In turn, these specimens have maintained catalytic response in long term, cyclic exposures to extremes in dissolved gases (or corrosion potential), impurity levels, pH, flow rate, temperature, straining, etc. With stoichiometric excess H2, the corrosion potential drops dramatically and crack initiation and growth are greatly reduced, even at high O2 or H2O2 levels. Without excess H2 (i.e., in normal BWR water chemistry), noble metals do not increase the corrosion potential or SCC. The success of this approach in minimizing H2 demand and dramatically
reducing corrosion potential and SCC is leading to its qualification for in-plant use.
Keywords: Stress corrosion cracking, noble metal catalysis, corrosion potential, crack grow th rate, crack initiation, stainless steel, nickel alloys, electroless plating, in-situ coating, high temperature water, boiling water reactors.