Hydrogen Water Chemistry (HWC) has been successfully employed to mitigate the IGSCC of BWR components in the recent years. However, to mitigate SCC in some vessel internals requires the use of high levels of feed water hydrogen, which results in high main steam radiation dose rate increases. Recent studies have shown that the presence of noble metals on these surfaces, by alloying or surface deposition by plating or various thermal spray coating techniques significantly reduced the hydrogen demand necessary to achieve the IGSCC protection potential of {minus}0.230 V(SHE). These techniques, although attractive, have some limitations because accessibility to individual components is a requirement for their successful application. This paper describes the concept of a novel method of applying noble metals potentially to all in-core wetted components by employing the reactor coolant water as the medium of transport for depositing noble metal on in-core metal surfaces. The concept of noble metal chemical addition (NMCA) technology has been successfully used in numerous laboratory tests to create a ``noble metal like`` (catalytic) surface on four of the major structural materials, Type 304 SS, Inconel 600, Alloy 182 weld metal and low alloy steel. The success of this technology has been tested using constantmore » extension rate tensile (CERT) tests, crack growth rate (CGR) tests and electrochemical corrosion potential (ECP) response tests. The NMCA technology has successfully decreased the ECP of surfaces below {minus}0.230 V(SHE), prevented crack initiation and mitigated crack growth rates in stoichiometric excess hydrogen in simulated boiling water reactor (BWR) environments, even at high oxygen or hydrogen peroxide levels. The NMCA treatment of surfaces has minimized the hydrogen demand necessary for IGSCC protection of the materials tested. Tests are in progress to qualify this process for operating BWRs.« less
Abstract The catalytic response and electrochemical polarization behavior of O2 and H2 reactions on noble metal-treated Type 304 (UNS S30400) stainless steel (SS) in high-temperature water containi...
Stress corrosion cracking (SCC), especially in existing boiling water reactor (BVM) components, is most effectively accomplished by reducing the corrosion potential. This was successfully demonstrated by adding hydrogen to BNM 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{sup 16}. 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 diffuse 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. 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. Inmore » turn, these specimens have maintained catalytic response in long term, cyclic exposures to extremes in dissolved gases, impurity levels, pH, flow rate, temperature, straining, etc. With stoichiometric excess H{sub 2}, the corrosion potential drops dramatically and crack initiation and growth are greatly reduced, even at high O{sub 2} or H{sub 2}O{sub 2} levels. Without excess H{sub 2} (i.e., in normal BWR water chemistry), noble metals do not increase the corrosion potential or SCC.« less
A stress corrosion cracking (SCC) model has been adapted for performance prediction of high level radioactive-waste packages to be emplaced in the proposed Yucca Mountain repository. For waste packages of the proposed Yucca Mountain repository, the outer barrier material is the highly corrosion-resistant Alloy UNS-N06022 (Alloy 22), the environment is represented by aqueous brine films present on the surface of the waste package from dripping or deliquescence of soluble salts present in any surface deposits, and the tensile stress is principally from weld induced residual stress. SCC has historically been separated into ''initiation'' and ''propagation'' phases. Initiation of SCC will not occur on a smooth surface if the surface stress is below a threshold value defined as the threshold stress. Cracks can also initiate at and propagate from flaws (or defects) resulting from manufacturing processes (such as welding); or that develop from corrosion processes such as pitting or dissolution of inclusions. To account for crack propagation, the slip dissolution/film rupture (SDFR) model is adopted to provide mathematical formulae for prediction of the crack growth rate. Once the crack growth rate at an initiated SCC is determined, it can be used by the performance assessment to determine the time to through-wall penetration for the waste package. This paper presents the development of the SDFR crack growth rate model based on technical information in the literature as well as experimentally determined crack growth rates developed specifically for Alloy UNS-N06022 in environments relevant to high level radioactive-waste packages of the proposed Yucca Mountain radioactive-waste repository. In addition, a seismic damage related SCC crack opening area density model is briefly described.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
