A reactor vessel consists of carbon/low alloy steel (SA508) as the structural material, and a cladding layer (SS309) as a protective layer. Cladding layer experiences damage by accidents such as thermal sleeve detachments. Carbon/low alloy steel is weak to corrosion when exposed to the primary water especially during refueling time, which is a potential threat against the integrity of a reactor vessel. Therefore, the damaged cladding part should be repaired. Repairing the inside of the reactor vessel is difficult because of high radiation levels, poor accessibility, and the underwater condition. One promising repair technology is the electrochemical deposition (ECD) of nickel.
Nickel plating through ECD has a lot advantages such as excellent corrosion resistance, no heavy thermal effect (near room temperature process), and proper mechanical properties for long-term nuclear operation. Moreover, the plating layer can be easily removed and is applicable to underwater conditions. The ECD technology used to repair the inside of the steam generator tube has been approved in the ASME code case N-569, titled “Alternative Rules for Repair by Electrochemical Deposition of Class 1 and Class 2 Steam Generator Tubing.” It is expected that an ECD layer can protect the corrosion/erosion of the exposed surface of damaged cladding/ carbon steel.
The ECD process consists of many processes, such as surface cleaning, strike layer formation for the adhesion between ECD layer and cladding/carbon steel, activation, and a main electrodeposition process. “Alternative Rules for Cladding Repair by Underwater Electrochemical Deposition in Class 1 and 2 Applications” is proposed based on the Code Case N-569. This proposed code case includes material requirements, qualification, essential variables, and examination requirements.
