Degradation of Aged Plants by Corrosion: Radiation-Induced Corrosion Cells Inducing “Long-Cell” Action

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In the previous papers, the author has established various ‘long cell’ corrosion configurations that should exist in nuclear power plants. With these corrosion mechanisms in place, the plant can be characterized as an assembly of gigantic short-circuited electrical batteries, inducing electrochemical corrosion at localized anodic sites. If these corrosion cells are involved at nuclear power plants, macroscopic electrochemical potential differences must be demonstrated between anodic sites where dissolution of metal (i.e. corrosion) is taking place and cathodic sites where deposition (also called sedimentation) of corrosion products are often observed. Among these, the radiation-induced corrosion cell is an important mechanism of corrosion issues among nuclear power plants, since it plays a major role in the corrosion problems found in primary water, including PWSCC and AOA in PWRs and IGSCC in the BWRs. There is numerous experimental evidence indicating a potential difference induced by radiation, however, the exact mechanism of such phenomena has not been investigated from the ‘long cell action’ corrosion hypothesis point of view. The author investigated the basic mechanism by combining radiation chemistry, electrochemistry and corrosion science to confirm the existence of radiation-induced ‘long-cell’ action (macro) corrosion cell. By performing a competition kinetic study, which is a simplified approach to determine which of several competing reactions will predominate, the hydrated electrons, e−aq, reacting mainly with stable molecules, are found responsible for inducing a large portion of the potential difference both in the PWR and BWR water chemistry environment. The hydrated electrons react with a cathodic half-cell included in the stable solutes thereby inducing redox reactions in the mixed cell configuration with both reducing and oxidizing actions. This method reproduces the reported experimentally observed ECP variation to a certain extent (observed in the INCA Test Loop in Sweden and NRI-Rez BWR-2 Loop in Czech Republic) which was measured by widely changing the solute concentrations, such as dissolved hydrogen and oxygen. The author believes the results support the assumed major reactions acting in the redox process.