Mitsubishi Nuclear Energy Systems, Inc. (MNES) has been awarded contracts at two nuclear power plants to provide its state-of-the-art water jet peening (WJP) services.
The WJP service will mitigate the potential for stress corrosion cracking of essential Alloy 600 components and associated weld metals, thus providing safety benefits and long-term cost savings to the ratepayers and utilities.
MNES will be responsible for overall project management, working with its parent company Mitsubishi Heavy Industries (MHI); with AZZ WSI, a specialty contractor based in Norcross, Georgia; and with Structural Integrity Associates Inc. (SI).
MHI will provide the specialized tooling and equipment necessary to complete the projects while AZZ WSI and SI will perform the on-site implementation work. SI will also provide engineering and licensing support. The WJP work at both facilities is currently planned for 2016.
The WJP process is used to modify material stress in important nuclear plant components and has been used successfully by Mitsubishi in 45 applications on 21 pressurized water reactors in Japan. Mitsubishi has developed the necessary technologies for testing and for contingency repairs. Mitsubishi also operates a complete training center in Japan for WJP services application.
A key advantage of WJP is that the entire process can be conducted underwater and uses only high-pressure water. No foreign materials are introduced into the reactor and no heat is applied to the material. The easy-to-operate equipment can be controlled remotely, allowing the procedure to be performed with low occupational doses. The work will be performed when the reactor is shutdown during a planned refueling outage.
"The water jet peening process provides an interior surface mitigation approach for reactor- vessel nozzle-dissimilar metal welds," said Rich Clemens, Vice President Strategic Projects for Wolf Creek. "This is a preferred approach due to our plant’s configuration and radiological conditions. Working together with Ameren Missouri is logical due to the common design of the Wolf Creek and Callaway plants. Additionally, we will be able to concurrently perform, within a reasonable outage schedule, WJP mitigation on the reactor vessel nozzles as well as on other less susceptible materials and welds located in the lower region of the reactor vessel. We have confidence that the process will provide mitigation of potential stress corrosion cracking."
