In this blog post, we will examine whether the safety of aging nuclear power plants can be judged solely based on their operating lifespan. We will also consider how to decide between shutting down or continuing to operate these plants, based on the safety assessments strengthened after the Fukushima nuclear accident, South Korea’s extended operation system, and the country’s electricity supply and demand situation.
Following the 2014 Sewol ferry disaster, public concern and anxiety regarding the safety of various facilities in South Korea increased significantly. Amid this social climate at the time, the Kori Unit 1 and Wolseong Unit 1 nuclear power plants—whose design lifespans were nearing their end or had already been exceeded—also became the subject of safety concerns. At the time, Gori Unit 1 was operating under an extended operating license after its 30-year design life had expired, while Wolseong Unit 1 was undergoing a review for extended operation following the expiration of its design life. In particular, during the early stages of the Sewol Ferry disaster, the extension of the ship’s operating period was cited as one of the causes of the accident, lending weight to arguments that the operation of nuclear power plants with extended design lives should also be halted. Furthermore, the media intensively reported on instances of malfunctions at aging nuclear power plants, highlighting the risks associated with them. However, it cannot be concluded that a nuclear power plant will necessarily experience more accidents or malfunctions than others simply because it has been in operation for a longer period. This is because the safety of a nuclear power plant must be assessed comprehensively, taking into account not only its age but also the condition of the equipment, age-related deterioration, inspection results, operational experience, and compliance with safety standards.
Given these instances that cast an unfavorable light on aging nuclear power plants, along with issues related to electricity supply and demand, the Fukushima nuclear accident, and the safety assessment system strengthened in the wake of the accident, it is necessary to consider whether it is reasonable to decide on the closure of aging plants based solely on their age. However, the situation has changed significantly between 2014 and the present. At that time, Kori Unit 1 and Wolseong Unit 1 were at the center of the debate over extended operation, but Kori Unit 1 was permanently shut down in June 2017, and Wolseong Unit 1 was also permanently shut down in December 2019. Currently, 26 reactors are in operation in South Korea, 4 are under construction, and the two units—Gori Unit 1 and Wolsong Unit 1—are permanently shut down. In 2024, nuclear power accounted for approximately 33.0% of total electricity generation. Therefore, rather than simply repeating the discussions surrounding those two decommissioned reactors, the current debate on aging nuclear power plants should focus on the reactors currently in operation that are being considered for extended operation beyond their design life, as well as the safety assessments associated with them.
In 2014, the 5th Basic Plan for Electricity Supply and Demand outlined a strategy to continuously increase the share of nuclear power, setting a target to raise it to 48.5% by 2024. However, this projection did not materialize, and power supply and demand policies have since undergone several revisions. The currently applicable 11th Basic Plan for Power Supply and Demand projects nuclear power generation at 248.3 TWh by 2038, with nuclear power expected to account for 35.2% of total electricity generation. At the same time, the plan outlines a strategy to expand the share of renewable energy generation to 29.2% and to increase carbon-free power generation, including nuclear power, renewable energy, and clean hydrogen and ammonia. Therefore, while nuclear power remains a key source of electricity under current policy, the system is shifting away from relying solely on nuclear power to meet demand toward a model that utilizes a mix of power sources. For this reason, the decision on whether to extend the operation of aging nuclear power plants should not be based solely on the ability to secure power generation capacity, but must also take into account safety, the power grid, and the feasibility of securing alternative power sources.
As of 2014, 23 nuclear reactors were in operation in South Korea, and 5 were under construction. At that time, the reactors that had exceeded their 30-year design life were Kori Unit 1 and Wolsong Unit 1. However, as the nuclear industry and regulatory environment have since changed, there are currently 26 reactors in operation and 4 under construction. Furthermore, Kori Unit 1 and Wolsong Unit 1 have already been permanently shut down. Therefore, it is not appropriate to simplistically predict the current situation by assuming that reactors must be shut down at regular intervals whenever a plant nears the end of its design life, as was the case in 2014. In fact, the Nuclear Safety and Security Commission is currently reviewing periodic safety assessments related to extended operation for several nuclear power plants and has already granted permission for the extended operation of Gori Unit 2 through 2025. This demonstrates the current institutional framework, under which the decision to continue operation is not automatically determined by a single figure—the design life—but rather is made after reviewing the condition and safety of each individual plant.
So, are there no safety concerns regarding the continued operation of nuclear power plants that have reached the end of their design life? The first thing to understand here is the concept of “design life.” Design life does not mean that all equipment at a nuclear power plant will necessarily become inoperable once that period has elapsed. Rather, it primarily refers to a design-specified period established during the plant’s design phase to ensure that specific structures, systems, and equipment can meet the required safety and performance standards for a certain duration. Therefore, the mere fact that a design life has ended does not mean that the plant immediately becomes dangerous or technically incapable of operation. The International Atomic Energy Agency (IAEA) also requires that, in cases of long-term operation, safety be verified for the extended operating period based on the management of aging degradation, safety assessments, and the results of periodic safety reviews. Although regulatory approaches vary by country, the United States employs a license renewal system, while many other countries utilize periodic safety reviews to assess whether a plant can operate safely beyond its originally designed operating period. South Korea also operates a regulatory system that combines these two elements.
The term “design life” can lead people to perceive that a nuclear power plant, like a human being, “reaches the end of its life” after a certain period and can no longer be used. However, what matters in actual nuclear power plant regulation is not simply how many years a plant has been in operation, but how effectively the age-related degradation that can occur over extended operation is managed. Since structural components, systems, and equipment in nuclear power plants can experience material degradation, corrosion, fatigue, aging, and technological obsolescence during long-term operation, these must be continuously monitored and managed. To permit long-term operation, it must be verified that such degradation does not impair safety functions, and facilities must be reinforced or replaced as necessary. Therefore, the argument that “it is dangerous because the design life has expired” is overly simplistic, and conversely, the claim that “there are no problems even after the design life has expired” is also overly simplistic. Operation beyond the design life must undergo separate safety verification and regulatory procedures, and the decision on whether to continue operation should be made based on the results.
One of the arguments cited by those advocating for the closure of aging nuclear power plants is the Fukushima nuclear accident in Japan. Although calls to highlight the dangers of aging nuclear power plants have grown louder since the 2011 Fukushima nuclear accident, an examination of how the accident unfolded reveals that it is difficult to attribute the cause solely to the age of the plant. On March 11, 2011, a magnitude 9.0 earthquake struck the Pacific Ocean off the coast of Japan’s Tohoku region, causing the reactors in operation at the Fukushima Daiichi Nuclear Power Plant to automatically shut down. Although external power was subsequently lost, emergency diesel generators and other systems activated, allowing the reactors’ safe shutdown functions to be maintained initially. However, a massive tsunami that followed flooded the plant, causing severe damage to emergency power sources and electrical equipment, and ultimately resulting in the loss of the power needed to maintain the reactors’ cooling functions. During this process, core damage and hydrogen explosions occurred, leading to a major accident involving the release of radioactive materials into the environment.
The Fukushima accident demonstrated just how vulnerable nuclear power plants can be to large-scale natural disasters. In particular, the fact that the simultaneous occurrence of an earthquake and a tsunami caused a chain reaction of damage to external power, emergency power, electrical equipment, and cooling systems served as a crucial lesson for strengthening nuclear safety standards in the future. Therefore, the lessons to be learned from the Fukushima accident go beyond the simple conclusion that “aging nuclear power plants must be shut down.” Key tasks now include enhancing defenses against large-scale natural disasters, strengthening response capabilities in the event of a loss of power, securing multiple means to maintain cooling functions, and reinforcing emergency response systems following a severe accident. At the same time, it is necessary to conduct a separate assessment of whether the aging of nuclear power plants could potentially affect their ability to respond to natural disasters or compromise key safety functions. In other words, while the Fukushima accident can be viewed in the context of the risks posed by aging nuclear power plants, the cause of the accident should not be reduced to the age of the plant alone. This should not be interpreted as justification for the continued operation of aging nuclear power plants, but rather as a case study illustrating which safety factors must be verified more rigorously when considering continued operation.
Following the Fukushima accident, stress tests were conducted in Europe to re-evaluate the safety of nuclear power plants. These stress tests were a comprehensive procedure designed to assess the plants’ ability to withstand extreme natural disasters such as earthquakes and floods, as well as their capacity to handle a total loss of power, loss of cooling functions, and major accidents—all based on the issues revealed by the Fukushima accident. It is important to note that the stress tests were not merely a mechanism for identifying and shutting down aging nuclear power plants. The core objective was to verify whether safety functions could be maintained under extreme conditions, regardless of the plant’s age, and to identify areas requiring additional improvement measures. Therefore, the examples from these stress tests also confirm that when assessing the safety of nuclear power plants, one must consider not only the plant’s age but also the actual condition of the facilities, accident response capabilities, and preparedness for situations exceeding design criteria.
In South Korea as well, as public concerns about nuclear power plant safety grew following the Fukushima accident, stress tests were conducted on plants operating for extended periods. At that time, Gori Unit 1 and Wolsong Unit 1 were among the primary targets, and the tests comprehensively assessed not only natural disasters such as earthquakes and tsunamis but also loss of grid power, management of severe accidents, and emergency response capabilities. However, current discussions on nuclear power plant safety should not rely solely on the stress tests conducted at that time. Currently, nuclear safety regulation in South Korea operates under a system that continuously verifies safety through procedures such as periodic safety assessments, reviews for extended operation, regular inspections, investigations into accidents and malfunctions, and the incorporation of operational experience. The Nuclear Safety and Security Commission is responsible for periodic safety assessments and reviews for extended operation of power reactors, and its regulatory duties include safety assessments for natural disasters exceeding design criteria. Safety assessments for nuclear power plants are still ongoing; for example, the Nuclear Safety and Security Commission recently reviewed the results of periodic safety assessments for Hanul Units 3 and 4 and Wolseong Units 3 and 4.
Among the nuclear power plants currently operating in South Korea, there are those that are nearing or have exceeded the operating lifetimes anticipated at the time of construction, and for which extended operation is under review. What is important here is not the mere fact that the plant is old, but rather verifying whether age-related degradation resulting from long-term operation can be properly managed, whether the plant meets the latest safety standards, and whether the safety functions of key structures, systems, and equipment can continue to be maintained. The International Atomic Energy Agency (IAEA) also states that for long-term operation, operators must utilize the results of safety assessments and periodic safety reviews, and establish management programs for the aging and degradation of structures, systems, and components to demonstrate that the necessary safety functions can be maintained throughout the extended operating period. In South Korea as well, reviews for continued operation are conducted in accordance with these principles; decisions on whether to continue operation are not based solely on whether “30 or 40 years have passed.”
A key point in the current debate surrounding the safety of nuclear power plants is that no one is claiming they are absolutely safe, nor is anyone asserting that they are particularly dangerous simply because they are old. Nuclear power plants are facilities that require a high level of safety management because accidents at these sites can have extremely significant social and environmental impacts. The Fukushima nuclear accident also demonstrated how large-scale natural disasters can threaten the safety functions of a nuclear power plant. Therefore, preparedness for natural disasters, responses to loss-of-power situations, maintenance of cooling functions, severe accident management, and emergency response systems must be continuously strengthened. At the same time, we must not make simplistic judgments about risk based solely on a nuclear power plant’s age. Rather, the older a plant is, the more rigorously we must monitor and inspect for age-related deterioration, reinforce or replace equipment, and verify compliance with the latest safety standards. Ultimately, the safety of aging nuclear power plants must be assessed based on the actual condition of the facilities and the results of safety evaluations, not on a single indicator such as age.
In 2014, given the power supply situation and nuclear power plant construction plans at the time, there were legitimate concerns about the impact that the sudden shutdown of aging nuclear power plants might have on the power supply and demand balance and on power plant construction costs. However, the power supply and demand environment has since changed, and the role of nuclear power must now be viewed within an energy system that utilizes a variety of power sources—including nuclear power, renewable energy, gas-fired power generation, and hydrogen and ammonia. The 11th Basic Plan for Electricity Supply and Demand also outlines a direction to maintain nuclear power as a key energy source while simultaneously expanding renewable energy and carbon-free power sources. Therefore, when deciding whether to extend the operation of aging nuclear power plants, one should not approach the issue solely based on the logic that “closing them would lead to a power shortage,” nor should one rely solely on the logic that “they are aging and must therefore be closed.” We must first verify whether safety standards are met, and then take into account power supply and demand, the feasibility of securing alternative power sources, grid stability, and economic costs.
Ultimately, the most important criterion for evaluating aging nuclear power plants should not be a simple number—such as “how many years have passed”—but rather the question: “Do they meet current safety standards, and can the age-related degradation resulting from long-term operation be properly managed?” Kori Unit 1 and Wolsong Unit 1 have already been permanently shut down, and in the case of Kori Unit 1, approval for decommissioning—the first of its kind in the country—was granted in 2025. However, the permanent shutdown of these two reactors does not mean that all nuclear power plants that have exceeded their design life must be handled in the same way. Conversely, one cannot automatically conclude that a nuclear power plant that has exceeded its design life is unsafe. The decision on whether to extend operation must be made through rigorous safety assessments of each individual plant and review by regulatory authorities. In fact, the International Atomic Energy Agency (IAEA) requires that, for long-term operation, periodic safety assessments and aging management programs be utilized to demonstrate the ability to maintain necessary safety functions throughout the extended operating period. In South Korea as well, such institutional decisions are being made in practice, as evidenced by the approval of continued operation for Kori Unit 2 and the safety assessments currently underway for several other nuclear power plants regarding continued operation.
Therefore, when discussing the shutdown of aging nuclear power plants, rather than jumping to conclusions based solely on the plant’s age, a comprehensive review is necessary that considers the results of safety assessments, the status of aging management, compliance with the latest safety standards, the ability to respond to natural disasters, major accident response systems, the power supply and demand situation, and the feasibility of securing alternative power sources. While it is clear that nuclear power plants are not absolutely safe facilities, the risks associated with nuclear power plants do not apply equally to all plants, nor are risks automatically determined simply because a plant is aging. Conversely, the simplistic assertion that “aging nuclear power plants are just ordinary nuclear power plants” is also insufficient from the perspective of current safety regulations. The older a nuclear power plant is, the more strictly its age-related deterioration and equipment condition must be managed; if it fails to meet safety standards, measures such as reinforcement, replacement, operational restrictions, or permanent shutdown must be taken. Ultimately, the decision regarding the continued operation or decommissioning of aging nuclear power plants must move beyond simplistic logic—such as “it must be shut down because it is old” or “it must continue operating because we need electricity”—and instead be based on an objective assessment of the safety of each individual plant and the results of that assessment. The call to decommission aging plants is not always a hasty one, nor is the decision to continue operating them always a dangerous choice. What matters is not the age of the plant, but rigorously verifying whether it can actually meet the safety requirements for both its current and future operating periods.
