Nuclear Safety After FukushimaEven with events at Japan's Fukushima Daiichi nuclear power complex still in a state of flux, attention is shifting from containment to assessment. The 9.0 magnitude earthquake, hundreds of aftershocks and ensuing tsunami were historic. But they can hardly be calledunforeseeable, and therein lies the nub of the critical questions this incident will raise for regulators everywhere: To what extent should nuclear safety regulation take account of all foreseeable contingencies, and should new technologies be required to apply to pre-existing facilities that were built to the standard of the industry at the time of construction?The six-reactor Fukushima Daiichi facility was commissioned in 1971 and—by design—successfully withstood the March 11 earthquake and its aftershocks. But the tsunami topped the facility's sea wall, knocking out the back-up diesel generator and forcing the pump cooling systems and pressure ventilators to rely on batteries until mobile generators could be delivered to the site. Water also flooded the basement where switching equipment connected the pumping equipment, impeding repairs.The result was overheating that caused pressure to build to over two times the designed limitations and led to explosions at three of the reactors. The outer buildings were designed to contain the reactor andto withstand severe weather conditions, but not hydrogen explosions. Radiation leakages resulted, causing widespread concerns about threats to health and the environment.Such a chain of events, however extraordinary, cannot be said to be unforeseeable. Japan's infrastructure and regulatory framework have anticipated earthquakes for 150 years; power outages, tsunamis and widespread demands that strain response efforts are all predictable consequences of earthquake risk.Indeed, engineers have already designed solutions to mitigate the risks that materialized at Fukushima. Today's third-generation nuclear reactors anticipate the possibility of failed cooling systems and hydrogen pressure build-ups. The Westinghouse AP1000 reactor has a series of passive cooling systems that operate without external ordiesel-generated power or activation by its operators. It also has recombiners that prevent hydrogen explosions.This design has been officially adopted in China for all inland nuclear projects where earthquake risks are more prevalent than on its coasts. Areva's EPR reactor under construction in Finland, France and China has four independent emergency passive cooling systems and extra core containment areas around the reactor. And Mitsubishi's new APWR has passive and active redundant cooling systems.So why weren't these technologies installed at Fukushima? Nuclear safety regulators around the world assess risks associated with nuclear power facilities on the basis of the technology to be deployed and the location and range of events that potentially could threaten the safety or control of the facility. Even after construction, regulators are given wide discretion to impose additional requirements on the equipment, systems and procedures used at a given facility.The problem is how to decide when to require plant operators to implement costly refits of new technology on older plants—and this is where Japan's regulators could ultimately come in for some justifiable scrutiny. This is a question of both engineering and cost-benefit analysis. While certain modular equipment and control systems in nuclear plants can be upgraded, integral parts of the reactor chamber or housing cannot be easily removed, disposed of and replaced due to the presence of radioactivity.This means that in some cases the choice may not be whether or not to upgrade, but whether to shut down entirely. Given those options, operators and regulators are inclined to maintain the status quo instead of requiring the application to old facilities of newer systems to more effectively address risks that can seem quite remote. Fukushima may cause a rethink of this approach not only in Japan but around the world.Japan's experience also suggests regulators and emergency planners need to think more realistically about the circumstances under which an emergency is likely to occur. Most nuclear safety regulations are based on a scenario where a singular disaster occurs at a specific facility—akin to Chernobyl or Three Mile Island, incidents that arose due to circumstances within the plants themselves or external events affecting their immediate vicinity.That approach to planning can leave officials unprepared for what has happened at Fukushima: a nuclear incident as part of a much larger disaster. In the aftermath of the Sendai earthquake, response teams and resources were required to cover an area of 35,000 square miles, in which two million people were without power, water or food, and roads, airports and other infrastructure were severely damaged. Morefar-sighted planning would have anticipated the limitations on emergency services in such circumstances.Finally, regulators need to account for the societies and particular cultures they cover. Japan's great wealth, technological advancement and quality infrastructure made it remarkably resistant to the ravages of a great earthquake and horrific tsunami. And the high levels of education and the renowned discipline of its people certainly helped it avoid apocalyptic consequences. While this hasn't averted the problem atFukushima, it does mean the country was better equipped to deal with such an event than others might have been.Regulators in Vietnam, Malaysia, Thailand, the Philippines, Indonesia and other developing nuclear aspirants that ring the fault lines of much of the Pacific Ocean need to candidly assess their nation's capacity to respond in similar circumstances. Would they have the resources to deal with a Fukushima-style incident, even apart from any question about the quality of pre-disaster planning?At some point in the future even the most modern nuclear power systems on today's drawing boards will appear antiquated compared to the day's technology. Fukushima should give regulators both today and tomorrow pause in how they approach the issue of safety in the face of technological evolution.(Mr. Stephens is a Hong Kong-based senior partner with the law firm Orrick, Herrington and Sutcliffe. )福岛核事故之后的核安全反思尽管日本福岛第一核电站仍然处于不稳定状态，但目前关注的焦点已经从控制转向评估。