ASME code for RPV cladding repair by Ni electrodeposition

SA508 low alloy steel of a reactor vessel was exposed to primary water in a pressurized water reactor(PWR) plant because the cladding layer of type 309 stainless steel of the reactor vessel experienced damage by an accident of thermal sleeve detachment. Repairing the inside of the reactor vessel is challenging because of high radiation levels, poor accessibility, and the underwater conditions. One promising technology is the electrochemical deposition (ECD) of nickel. Nickel plating through ECD has a lot advantages such as an excellent corrosion resistance, no heavy thermal effect (near room temperature process), and proper mechanical properties for long-term operation. The ECD technology used to repair the cladding was approved in 2013 as the ASME code case N-840(CC N- 840). The new code case is based largely on the groundwork of the CC N-569. Technical background of the new code case N-840 was published in some journals and the PVP2013-97857 paper. The CC N- 840 defines the requirements and variables controlled by the ECD in underwater cladding repair applications. Based on the code case, a three-year project to develop a new application technology was started to repair the damaged cladding in 2017. The objectives of the project are (1) to set up Ni plating essential variables in terms of practical application, (2) to support a repair organization with cladding repair tool development. This includes work supporting the utility with permission from the regulatory organization. This article aims to address the three-year effort of the code case development process in the ASME section XI committee and the current status of its application to develop a new application technology. Damage to the stainless steel clad of the reactor vessel due to a detachment of the thermal sleeve was reported in 2003, and the base metal of the SA 508 reactor vessel steel was exposed to primary coolant for over 14 years. Corrosion rate monitoring has been conducted using a replication method during every outage. An ASME Section XI code case was developed in 2013. A new research project began to repair the damaged area in 2017.