"Validation at Kori Units 2 and 3" New Technology Developed for Assessing Integrity of Nuclear Power Plant Equipment

A new technology has been developed to assess the integrity of nuclear power plants (NPPs) that have been shut down for extended periods.

The Korea Atomic Energy Research Institute (KAERI) announced on April 22 that the research team led by senior researcher Sunhyuk Jeon and postdoctoral researcher Sungjun Ha at the Department of Materials Safety Technology has developed a technology capable of accurately measuring the degree of corrosion in secondary system equipment at long-term shutdown NPPs.

Dr. Sungjun Ha, Postdoctoral Researcher (left), and Senior Researcher Sunhyuk Jeon (right), developers of air corrosion evaluation technology. Korea Atomic Energy Research Institute

Typically, when a nuclear power plant is not operated for a long time, the secondary system piping and key equipment, in addition to the reactor itself, are managed in a dry state by draining out water. In this situation, the piping and equipment are exposed to air, which can lead to corrosion of the facilities. However, precisely measuring the degree of corrosion has proven to be difficult.

Generally, the corrosion rate of metals is determined by measuring the weight change that occurs when an oxide film forms on the surface. However, in the case of NPP equipment, direct measurement of weight change is not feasible, so a method has been used in which samples are taken directly from the equipment surface to estimate the degree of corrosion.

The problem with this approach is that, in nuclear power plants, it is difficult to clearly distinguish between the oxide film that formed during operation and the additional oxides that formed after shutdown due to air exposure when analyzing samples.

In contrast, the technology developed by the research team utilizes a surveillance specimen to measure the degree of corrosion in secondary system equipment and other components that are exposed to the atmosphere in a nuclear power plant.

First, specimens are prepared from carbon steel, the material used for secondary system piping in NPPs, and an oxide film that would have formed during normal operation is artificially created on these specimens through an oxidation process. The specimens are then installed inside equipment that is managed in a dry state after plant shutdown. After a certain period, the increase in weight of the specimens is measured. The research team explained that this enables a quantitative assessment of the corrosion rate.

This technology, unlike the conventional method of directly sampling equipment surfaces, does not affect the original structure of the equipment. It also allows for the accurate distinction and measurement of corrosion that occurred only after the plant was shut down and exposed to air.

Most importantly, because surveillance specimens can be installed at various locations, it is possible to systematically track corrosion characteristics at different sites. This makes it possible to establish customized maintenance standards and strategies for each piece of equipment.

Surface and cross-section of the surveillance specimen developed by the research team. Korea Atomic Energy Research Institute

The research team also applied and validated this technology at Kori Unit 2 (which passed the continued operation review) and Kori Unit 3 (currently under review for continued operation). During the validation process, the team confirmed that the technology can improve the reliability of integrity assessments during long-term dry storage and provide necessary data to inform decisions regarding continued operation of NPPs.

Restarting a nuclear power plant that has been shut down for an extended period requires a continued operation license, and obtaining such a license can take several years. Given this, the number of long-term shutdown NPPs is expected to steadily increase in the future, highlighting the significance of the integrity assessment technology developed by the research team.

Kim Dongjin, head of the Department of Materials Safety Technology at KAERI, stated, "This new technology overcomes the limitations of previous methods and provides an innovative assessment tool that reflects the actual corrosion status of secondary systems in nuclear power plants." He added, "KAERI will continue to contribute to strengthening the integrity of NPPs by systematically maintaining equipment in line with the trend toward continued operation of domestic nuclear facilities."

This research was supported by the Ministry of Climate, Energy and Environment. The results were recently published online in the international journal 'Nuclear Engineering and Design' in the field of nuclear engineering.

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