This blog post explains why decontamination technology is considered the most critical step in the decommissioning process of aging nuclear power plants. It examines the principles of radiation removal and the technical challenges involved, outlining the essential conditions for safe decommissioning.
On June 19, 2017, Unit 1 of the Kori Nuclear Power Plant in South Korea permanently ceased operations. Operating for 40 years, Gori Unit 1 experienced multiple incidents, including a complete blackout in February 2012. These cases served as key evidence supporting the argument for closing and decommissioning aging nuclear plants. With operations halted, Gori Unit 1 now enters the decommissioning process, which will take at least 30 years until the site is restored. Nuclear power plant decommissioning refers to the process of safely and economically handling various types of nuclear facilities that have reached the end of their operational life. Because the work must be performed under conditions involving radiation exposure, nuclear decommissioning requires technology that integrates multiple disciplines such as chemistry, radiation engineering, and mechanical engineering. This blog post aims to explain the strategies and processes of nuclear decommissioning, as well as the future of nuclear decommissioning technology.
Nuclear power plant decommissioning strategies are determined based on regional technical and policy variables. They are broadly categorized into immediate dismantling and deferred dismantling, based on the waiting period before decommissioning begins. Immediate dismantling involves waiting until the radiation levels in the buildings and site fall below a certain threshold before proceeding with dismantling. This strategy allows for dismantling within a relatively short period of about 15 years and facilitates environmental restoration afterward. However, it is criticized for the high risk of radiation exposure since work must proceed while some radioactivity remains, and for generating large quantities of radioactive waste. In contrast, deferred dismantling involves waiting until radioactive materials decay naturally before proceeding with dismantling. Managing the facility while waiting for radioactive material decay requires approximately 60 years, while sealing the facility with concrete structures requires over 100 years. Although the long-term decontamination process reduces radiation exposure risks and waste generation, it has limitations: high ongoing management costs and difficulties in post-decommissioning environmental restoration and site reuse.
Nuclear power plant decommissioning involves six stages: shutdown, preparation for decommissioning, decontamination, dismantling, waste disposal, and environmental restoration. The core processes are decontamination and dismantling, which remove radiation from inside the plant. Decontamination is a technology that selectively removes only the radiation-contaminated parts; the amount of radioactive waste can be reduced depending on the decontamination technology applied. Key decontamination targets include aged cooling water pipelines and the thin, hard oxide film, several micrometers (μm) thick, formed on the surface of spent nuclear fuel. This oxide film contains various contaminants, including radioactive cobalt leaked from the nuclear fuel. To remove this material, which is difficult for humans or machines to remove directly, several decontamination technologies have been developed. Representative methods include alternately injecting solutions containing reducing agents and oxidizing agents to clean vessels and piping, or spraying high-pressure water inside the facility to ablate surfaces. Research is also underway to enhance decontamination efficiency by using foam-form decontamination solutions, which have a larger surface area than liquids.
Decommissioning is the process of cutting and dismantling the entire facility after decontamination. The most challenging item to handle in this process is spent nuclear fuel. Reactors are difficult to fully decontaminate, and the nuclear fuel itself emits strong radiation, creating an environment where human workers cannot perform decommissioning tasks directly. Therefore, robotic arms replace human workers in decommissioning. Workers open the reactor lid, insert a robotic arm connected to a crane, and then seal it. The robotic arm precisely cuts only the contaminated sections, places them into containers, and after the work is complete, transports them to a radioactive waste processing facility. Robots for nuclear power plant decommissioning must operate stably under harsh conditions, such as radiation exposure, and since they handle radioactive materials, remote precision control capabilities are essential. In Korea, the Korea Atomic Energy Research Institute (KAERI) is developing a cutting robot for the decommissioning of Gori Nuclear Power Plant Unit 1, while the Ulsan National Institute of Science and Technology (UNIST) has also announced plans to develop nuclear decommissioning robots. Notably, the robot under development by KAERI is designed to perform reactor inspections during plant operation and, in the decommissioning phase, to be equipped with arms capable of cutting and welding.
The disposal of radioactive waste remaining after decommissioning is another critical challenge. Radioactive waste is classified as low-level or high-level based on its radioactivity concentration. Low-level waste can be compacted, solidified in cement, and buried several meters underground. The problem, however, lies with high-level radioactive waste. Most high-level waste consists of vitrified solid waste generated during the reprocessing of spent fuel. The technology for its complete disposal has not yet been developed. The most realistic method involves burying the waste in deep geological formations at least 300 meters underground and installing concrete walls to block radiation leakage. However, this too is not yet considered a complete solution due to issues like inadequate criteria for selecting disposal sites.
Radioactive waste isn’t limited to solids. As seen in the Fukushima nuclear accident, large volumes of contaminated water containing radioactive materials can also be generated. In Fukushima, purification facilities are operating that separate radioactive substances by passing the contaminated water through highly absorbent zeolite. However, this method does not remove radioactive substances; instead, it accumulates them in the facility’s filters or waterways, ultimately creating new radioactive waste. In 2017, the Korea Atomic Energy Research Institute developed a technology to purify radioactive contaminated water using microorganisms. This technology involves introducing radiation-resistant microorganisms into the contaminated water. Through biological sulfidation reactions, it converts radioactive cesium into crystalline form and precipitates it. It is considered an environmentally friendly technology because it effectively removes cesium, which is generally difficult to precipitate, without generating additional waste.
According to the Nuclear Safety and Information Center, the operational lifespans of 12 Korean nuclear reactors, including Gori Unit 1, are scheduled to expire by 2030. As the number of aging reactors increases, the demand and necessity for nuclear decommissioning technology will grow significantly. Not only Korea, but also countries heavily reliant on nuclear power like France, the UK, and the US are facing increasing burdens from aging reactors. However, unlike Korea, where the institutional foundation is not yet fully established, these countries have already developed policies and technologies for nuclear decommissioning. Representative models include the government-led approach (France, UK), where the government spearheads decommissioning projects, and the private-sector-led approach (US, Germany), where private companies lead decommissioning while the government handles regulation, management, and supervision.
Developing nuclear decommissioning technology is far from simple, requiring complex integration of technologies across diverse fields and proceeding in phases over decades. To safely decommission Korea’s aging nuclear plants and, further, contribute to solving the global challenge of nuclear decommissioning, continuous development and investment in this technology are essential.
