The Chernobyl disaster may have marked the end of the long period of nuclear exuberance, in which experimental reactors were assembled in the desert, bolted into boats, shot into orbit, buried in arctic ice, and built to test exotic ideas. Every nuclear power reactor that was built in the United States was experimental. There was no standard design, and no two reactors were exactly alike. Even in a plant with two, identical-look­ing reactors, built by the same manufacturer, the two units were not exactly the same, requiring unique operator training and different spare parts. It was a massive engineering experiment in which much was learned, by trial, error, and accident investigation.

A point that was definitely learned was how not to build a nuclear reactor. So many designs that now seem obviously flawed had to be tried, and from all the large and small failures came a condensation of wisdom, pointing toward inherently safe, accident-free nuclear reactor designs. The path to a safe reactor is not necessarily coincident with a path to the least expensive reactor, and that is the hardest lesson of all to learn. The cheapest, simplest construction may also be the best construction, although not necessarily, and in nuclear power the path of success must follow the safety path.

Nuclear power has been in a holding mode for the past 30 years, nei­ther moving forward nor receding. As it has remained dormant, the needs of the industrial world have changed. Atmospheric chemistry and general environmental pollution have become factors in power generation deci­sions. Global warming and air pollution are larger issues now than they were 30 years ago, and burnable materials such as coal, oil, and natural gas are now seen as finite resources. Because of all these factors, nuclear power generation is being given a second look.

On March 11, 2011, the expansion of nuclear power was once again challenged when the biggest earthquake in the history of Japan occurred off the northeast coast of the main island, Honshu. Minutes later, a power­ful tsunami struck, wiping out entire towns and killing tens of thousands of people. Although designed for the maximum expected seismic activity, nuclear plants located on the beach faced the full force of the quake and tsunami. Closest to the quake, Onagawa, Tokai, and Fukushima II suf­fered complete automatic shutdowns. Fukushima I also shut down three reactors that were running but lost the use of its emergency diesel genera­tors in the tsunami. There was no power to run coolant pumps, and the situation slowly progressed over days from serious to destructive. Reac­tor cores, still hot from having run continuously for years at full power, melted, and reactor buildings exploded from hydrogen gas buildups. Fis­sion products escaped and polluted Japan and the Pacific Ocean. Reper­cussions and rebuilding from this massive human and economic disaster will continue for years.

Japan is recovering, and the need for nuclear power in this island nation and the world are still there. Expansion of nuclear power proceeds, using better and stronger reactors, designed for safe cooldown even when all power, including emergency generators, has been lost. Over the past 30 years, the nuclear industry has been refining and implementing safety procedures and systems, improving training, and always learning from mistakes and acts of nature, small, large, and calamitous.