The harnessing of the atom in the 1940s changed the nature of war forever, offered a new source for electrical power generation, and improved medical diagnostic techniques. The awesome and compact power of nuclear arms has transformed the military arsenals, strategies, and psyches of nations around the world. It has also greatly improved the range and comfort of submarines, and had a significant impact on peacetime activities. Nuclear technologies have stirred emotions and controversy, but the engineering achievements related to their development remain among the most important of the 20th century.

Einstein's relativity theory marked, above all, the point from which there was no return. The inevitable development that changed the world, however, occurred in 1942, when Enrico Fermi conducted the first controlled chain reaction, releasing energy from the atom's nucleus. The developments that immediately followed were directed by Robert Oppenheimer, working with engineers and physicists from the Los Alamos National Laboratory in New Mexico. Their work came amid worldwide competition to be the first to have the atom bomb as a defense priority in World War II. The nature of war changed when the United States dropped atomic bombs on Hiroshima and Nagasaki in 1945. The nuclear arms race began full-blown in 1949 when the Soviet Union exploded its first atomic bomb. As a destructive power the atomic bomb has been unequalled, and its potential threat alone drives peace and war initiatives worldwide.

Peacetime uses were pursued with equal fervor with the first nuclear-reactor radioisotopes for civilian medical use delivered in 1946. Both military adaptation in submarines and aircraft carriers and the use of nuclear energy for commercial power plants resulted from this work. Admiral H. G. Rickover led engineers to pioneer new materials, design reactors, develop an industrial base, establish safety and control standards and operating procedures, organize training programs, and build and test full-scale propulsion prototypes. The nuclear submarine is an engineering masterpiece which has withstood practical service with unblemished records.

Rickover also directed work at the Westinghouse Bettis Atomic Power Laboratory and the GE Knolls Atomic Power Laboratory to develop the Pressurized Water Reactor (PWR) in 1953. These reactors ultimately became the mainstay design of commercial power stations. Ceramics -- as fuel pellets, control rods, high-reliability seats and valves, and containerization -- were a critical feature of the PWR. The first nuclear reactor system to produce electric power commercially in the United States was in 1957 at Shippingport, Penn. (retired in 1982). It was a joint effort by the Duquesne Light Company, Westinghouse, and the U.S. Naval reactor program. The first major nuclear power plant in England opened in 1956.

Through most of the 20th century energy production has relied on fossil fuels. Consumption increases globally, while these fuel sources race towards being exhausted. The International Energy Agency projects a 65 percent growth in world energy demand by 2020. Engineers worldwide have made impressive strides in the use of nuclear fission for electrical power production.

The great advantage of nuclear power is its ability to extract enormous energy from a small volume of fuel. Nuclear fission, transforming matter directly into energy, is several million times as energetic as chemical burning. One metric ton of nuclear fuel produces energy equivalent to 2 to 3 million metric tons of fossil fuel (1 kilogram of coal generates 3 killowatt-hours of electricity; 1 kilogram of oil 4 killowatt-hours; 1 kilogram of uranium fuel in a modern light-water reactor generates 400,000 killowatt-hours; and if uranium is recycled, 1 kilogram can generate more than 7,000,000 killowatt-hours). A 1,000-megawatt-hour nuclear plant releases no noxious gases or pollutants and less radioactivity per capita than is encountered from airline travel, a home smoke detector, or a television set. Nuclear power is meeting the annual electrical needs of more than 1 billion people with more than 400 operating reactors worldwide, most in Europe, Sweden and the United Kingdom. Nuclear energy accounts for about 20 percent of power production in the United States.

Nuclear safety and efficiency have improved significantly since 1990. New generations of small, modular power plants are on the horizon. A South African utility has announced plans to market a modular gas-cooled pebble-bed reactor that does not require emergency core-cooling systems and physically cannot "melt down." MIT and the Idaho National Engineering and Environment Lab are developing a similar design to supply high-temperature heat for industrial processes such as hydrogen generation and desalinization.

Japan has begun using recycled uranium and plutonium mixed-oxide (MOX) fuel in its reactors and will use 100-percent MOX fuel by 2007. France and the United Kingdom currently reprocess spent fuel; Russia is stockpiling fuel and separated plutonium for jump-starting future fast-reactor fuel cycles. Engineering techniques to recycle spent fuel can extend the world's uranium resources and make it possible to convert plutonium to useful energy while breaking it down into shorter-lived, nonfissionable, nonthreatening nuclear waste. Nuclear waste is not an engineering problem, as advanced projects in France, Sweden, and Japan demonstrate. Rather, it offers solutions to energy needs. The safety record in more than 40 years of commercial nuclear power operations demonstrates that this is much safer than fossil-fuel systems in terms of industrial accidents, environmental damage, health effects, and long-term risks.

Innovations in reactor and shielding design have achieved considerable success. New mathematical methods, new measurement technology, new fuel-element production, and a new metallurgical science evolved with this technology. Basic engineering equations had to be reconsidered in light of new chemical elements and nuclear reactions. Design of safe nuclear energy conversion systems required extensive programs of fluid and thermal hydraulic measurements, expanding the field of engineering itself. Process control depended on invention and commercial development of new instrumentation. Even accidents, such as Three Mile Island (1979) and Chernobyl (1986), have led to improvements in core-damage limitations, containment integrity, and radiological hazard studies.

In the 1950s, nuclear development was actively pursued in Europe, resurging in the United States in the 1960s and 1970s, with Europe and the Far East having the greatest growth in activity since then. Safe disposal of nuclear waste and the optimization of process design continue to require cooperative efforts among engineers on a global scale. While the United States hasn't built a nuclear power plant since 1980, the rest of the world continues to develop this technology. In the context of the Kyoto Protocol, an international treaty that calls for the reduction of emissions to 7 percent below 1990 levels by the year 2008, nuclear power plant development may once again fail to meet expectations. The challenge for engineers remains to design and operate nuclear plants to perfect this technology. Worldwide adoption of safe and cost-efficient nuclear-energy programs will affect these greenhouse and other pollution issues.

Because of its lack of emissions, nuclear energy has potential over fossil-fuel technology as a lasting solution to energy demand. Projected global warming and international hostilities over scarce energy supplies also drive engineers to find solutions toward adopting nuclear and other renewable sources. Furthermore, what has been learned from these technologies-the use of radiation, particularly for medical diagnosis and treatment-has and continues to improve our lives.