"Even Shutdown Nuclear Plants Age"... Path Opened for Precise Measurement of Atmospheric Corrosion [Reading Science]

Demonstrated at Kori Units 2 and 3
Enhancing Reliability of Equipment Integrity Assessments During Long-Term Shutdowns

For the first time in Korea, a technology has been demonstrated that can precisely measure the "invisible aging" of nuclear power plants (NPPs) that have been shut down for extended periods. By enabling the separation and quantification of atmospheric corrosion inside pipes and equipment left in a dry state, this advancement is seen as establishing a critical foundation for securing core data needed to determine whether to continue operating nuclear power plants.

On April 22, the Korea Atomic Energy Research Institute announced that it had developed a technology to precisely measure the level of atmospheric corrosion occurring in the secondary system equipment of long-term shutdown NPPs using "surveillance specimens."

Comparison before and after atmospheric corrosion of surveillance samples. Provided by the research team

NPPs can be taken offline for extended periods for maintenance, regulatory approval, or other reasons. During such shutdowns, secondary system pipes and major equipment outside the reactor are managed in a "dry state," with all water removed. The challenge lies in the fact that corrosion progresses on metal surfaces exposed to air during this process, but until now, it has been difficult to accurately distinguish and measure the extent of this corrosion.

Precisely Isolating "Post-Shutdown Corrosion" Without Equipment Damage

The conventional method involved directly extracting samples from equipment surfaces to estimate the degree of corrosion. However, it was difficult to distinguish between oxide films formed during operation and new oxides formed after shutdown, making it challenging to separately assess "corrosion that occurred during the shutdown period."

The core of the newly developed technology lies in the use of "surveillance specimens." The research team fabricated specimens based on carbon steel used in secondary system pipes and artificially reproduced the oxide film created during normal operation. After installing these specimens inside the equipment following plant shutdown, they measured weight changes after a certain period and quantitatively converted these measurements to determine corrosion rates.

This method enables the evaluation of corrosion status without damaging the equipment and, crucially, allows for the separate measurement of "atmospheric corrosion that occurred after shutdown." Furthermore, by installing specimens at various locations inside the equipment, it is possible to systematically track corrosion characteristics, making it useful for developing customized maintenance strategies for each facility.

Dr. Sungjoon Ha, Postdoctoral Researcher (seated), and Dr. Sunhyuk Jeon, Senior Researcher at the Korea Atomic Energy Research Institute, who developed a long-term shutdown nuclear power plant equipment standby corrosion evaluation technology using surveillance specimen. Provided by Korea Atomic Energy Research Institute

The research team applied this technology to Kori Unit 2 and Kori Unit 3, successfully completing demonstration tests. Kori Unit 2 recently passed its continued operation review, while the review for Kori Unit 3 is currently underway.

Considering that the approval process for continued operation of NPPs can take several years, the importance of managing equipment during long-term shutdowns is expected to increase further. This technology is anticipated to enhance the reliability of equipment integrity assessments during dry management periods and provide essential empirical data needed to determine whether continued operation is feasible.

Kim Dongjin, Director of the Materials Safety Technology Division at the Korea Atomic Energy Research Institute, stated, "This evaluation technology overcomes the limitations of existing methods and can reflect the actual corrosion status. It will contribute to raising the level of equipment integrity management in line with the expanding trend of continued operation at domestic nuclear power plants."

This content was produced with the assistance of AI translation services.