The implications of Fukushima

Abstract

The effects of the tragedy at Japan’s Fukushima power plant will continue to reverberate over the upcoming weeks, months, and years. And, as the writers in this symposium explain, the consequences of the disaster go beyond Japan—like Chernobyl and Three Mile Island, Fukushima will reshape nuclear agendas and policies in countries around the world. In this Global Forum, leading experts reflect on the current and future implications of Fukushima for their own countries—the United States, the European Union, and South Korea. Mark Cooper (2011) writes from the United States; Caroline Jorant (2011) from the European Union; and Soon Heung Chang from South Korea. In August, this forum will continue as a Roundtable at www.thebulletin.org.

Japan is one of the world’s top countries in terms of managing its nuclear power plants. Yet when a massive earthquake and tsunami rocked its northeastern shore in early April, crippling a nuclear facility in the prefecture of Fukushima, the country found itself shocked and helpless in the face of an unforeseen nightmare. The threat of a nuclear disaster suddenly seemed very real for every country with a reactor in its midst—South Korea, where nuclear power accounts for 31 percent of the country’s energy consumption, was no exception. South Korea is positioned to be one of the biggest exporters of nuclear technology in the next 20 years and plans to begin building reactors with a 100-percent South Korean pedigree by the end of next year. Because of South Korea’s role as an innovator and exporter, the lessons of Fukushima—both technical and systemic—are lessons for not only South Korea, but for the world. South Korea must pay close attention to Fukushima if it hopes to keep nuclear reactors politically viable and safe.

Technical issues

Emergency cooling

The fundamental cause of the Fukushima accident was a tsunami-induced power outage, not the massive earthquake itself. The lesson here is that multiple emergency power-supply systems should be in place to ensure that the flow of electricity will not be interrupted—even in the event of an earthquake, tsunami, terrorist attack, or any other external event. These emergency systems should include external and portable power sources that can survive a natural disaster so that nuclear facilities stay on track during an emergency, even in extreme conditions such as a station blackout. It is also essential to secure emergency water sources that can be used when the emergency cooling system of a power plant becomes dysfunctional, as a final means of cooling reactors. Such emergency water-supply systems must be connected to the emergency power system so that they are available for immediate use. South Korea’s APR 1400 and APR+ reactors—among the safest designs in the world—were improved so that a water refueling storage tank is placed inside the containment building, rather than outside. This change helps secure the emergency cooling water.

Spent fuel storage pools

One unexpected problem during the Fukushima accident was related to spent fuel pools located within the reactor building of unit 4. The loss of power led to problems with cooling the spent fuel, which was kept in storage pools without any containment other than the buildings, and thus posed serious risks for the release of radioactive materials.

With this in mind, the emergency power-supply systems for domestic spent fuel storage facilities need to be reexamined. Stricter guidelines for the cooling of spent fuels should be introduced, such as deploying passive cooling systems that can remove residual heat even in the event of a total power loss. The structural rigidity of storage buildings should also be enhanced in order to prevent radioactive materials from being released into the atmosphere during an accident.

For some of its Canada Deuterium Uranium reactors (CANDU), South Korea uses dry-cask storage, meaning spent nuclear fuel is stored inside concrete casks, where it is cooled by natural air circulation. ¹ Because this system does not require electricity, it works well in situations similar to that at Fukushima, but the dry-cask containers should be reinforced against any potential earthquake or other external calamity.

Hydrogen control system

During the Fukushima crisis, hydrogen accumulated and exploded in the upper part of the reactor building, which lacked a system for hydrogen control. To prevent a hydrogen explosion in the event of a severe accident, plant managers can install a safety device that helps reduce hydrogen buildup. There are several designs to choose from: a hydrogen igniter, which deliberately burns the hydrogen before it can reach explosive concentrations; different kinds of hydrogen recombiners, which use various mechanisms to force the hydrogen to react with oxygen to produce water; or a passive autocatalytic recombiner, which is similar to the hydrogen recombiner but uses heat from the steam to circulate air through the catalytic plates. All but the passive autocatalytic recombiner require an external power supply, so it is crucial not only to re-examine the safety of existing facilities but also to incorporate additional passive measures, meaning systems that do not require human intervention.

The hydrogen control systems were added to South Korea’s Kori nuclear power plants years ago, but these systems must be both inspected and improved at the country’s remaining plants.

Probabilistic safety assessment

The recent nuclear disaster in Japan was an accident caused by unpredictably extreme external events. Probabilistic safety assessments currently performed in nuclear power plants are structured around mostly predictable scenarios, but the possibilities of wide-ranging, unpredictable external risks should be incorporated into probabilistic safety analysis. The safety of existing nuclear power plants should be reassessed and their vulnerabilities identified. Depending on the findings, facility upgrades may be needed to improve nuclear safety.

Within weeks of the Fukushima disaster, nuclear power plants operating in South Korea were re-examined extensively, and the results have shown satisfactory progress so far. But enhanced probabilistic safety analysis methods should be applied comprehensively and continuously in the future.

Passive safety systems

The Fukushima accident would have been minimized if there had been some cooling via natural circulation that could have persisted after the power outage. Such passive safety systems need to be enhanced: They must become operable automatically (in other words, passively), either by gravity or other natural forces, so that cooling, hydrogen control, and measurements of temperature, pressure, and radioactivity can continue even when power supplies and pumps shut down.

In South Korea, these passive safety features were designed for the APR+ reactor, but have yet to be commercialized. These designs, for example, feature two systems that could be used for decay heat removal: a natural circulation system, or a passive containment cooling system with internal or external condensors. Such safety features should be improved and employed, especially in future plants, in order to provide better safeguards against emergency situations in which power supplies are completely lost.

Systemic issues

Advance planning

In South Korea, as well as around the world, emergency planning manuals at all nuclear plants should be updated to outline organized and prompt responses—instead of makeshift ones—to potential accidents. These responses should take into consideration the various scenarios in which severe accidents can result from things like earthquakes, tsunamis, terrorist attacks, power outages, and plane crashes. Although such an accident has yet to befall South Korea, preparedness remains as essential as ever.

Personnel management

One of the problems revealed by the Fukushima accident was the lack of specialized personnel able to respond appropriately in times of crisis. The initial response is vital in nuclear power plant accidents, and there is a pressing need for specialists who can take prompt action with prudent judgment. What is needed in the case of an accident like that at Fukushima is a “control tower” of sorts where fast-paced and accurate decisions can be made—as opposed to numerous individuals and organizations moving about in confusion—as well as a solid delivery system that can efficiently convey and implement directives from this central station. In order to secure high-quality human resources, more talented personnel should be cultivated, and practical training should be provided so that key operators can develop a better understanding of the characteristics of nuclear power plant operation, as well as plant behaviors and possible responses in the event of an accident.

Safety-related research

In South Korea and around the world, it is crucial that design standards be strengthened enough to withstand earthquakes and tsunamis—the natural disasters that, either directly or indirectly, led to the Fukushima accident—and that new measures be developed to deal with the effects of such disasters. Further research related to severe accident scenarios is needed for these areas in particular: new power-supply systems that guard against the worst power-system accidents; hydrogen control systems that work even in the event of a station blackout; more versatile pump systems; and passive and natural-convection cooling systems. The research findings should then be incorporated into not only the design but also the manuals of new nuclear power plants. At the same time, creative ideas and technologies must be developed so that the economics of new nuclear power plants will not be considerably undermined as design standards are improved on the basis of the findings.

Information exchange

A network of relevant institutions and nuclear-safety experts should be established so that the international community can respond more effectively to possible emergencies. It is crucial that countries with nuclear plants promote research and development with regard to better safety, communication, and cooperation among all stakeholders. A system of cooperation between industry and academia, centered at specialized research institutes, should be strengthened. It is also important to reinforce international cooperation so that neighboring countries can exchange essential information and coordinate responses in the event of a nuclear accident.

Throughout the Fukushima crisis, an informal network of nuclear experts in South Korea and Japan has been helpful in relaying and exchanging real-time information; as fears escalated that radiation from Japan would reach South Korea, this open communication helped to assuage those fears. This experience demonstrates the importance of maintaining close ties between all experts and stakeholders in the nuclear field.

Public acceptance

Despite the safety standards featured in South Korea’s nuclear reactor designs, the possibility of unexpected accidents will always remain. Therefore, it is extremely important to establish a culture of safety and precaution for operators and other workers engaged in the nuclear industry. Individual workers should fully recognize the importance of nuclear safety, and administrators and nuclear organizations as a whole should develop a safety-oriented attitude that encourages strict and prudent approaches in their operations. In South Korea, the image of nuclear power remains somewhat negative in the public mind, and the recent accident may only exacerbate this. An improved safety-oriented mindset could help to alleviate these popular concerns. Extensive efforts should be made to promote public understanding of nuclear energy by providing and publicizing accurate, fact-based information.

The recent accident has proven once again that ensuring a high level of safety is of immeasurable importance in the use of nuclear energy, and it should inspire the global nuclear industry to comprehensively reexamine the design and operation of its nuclear power plants. Against this backdrop, South Korea should take the Fukushima crisis as a unique opportunity to review and improve its nuclear safety.