In a nuclear fission reaction, the nucleus of a heavy element, such as uranium, splits when bombarded by a free neutron in a nuclear reactor.(1) The fission process for uranium atoms yields two smaller atoms, one to three free neutrons, plus an amount of energy. Because more free neutrons are released from a uranium fission event than are required to initiate the event, the reaction can become self sustaining--a chain reaction--under controlled conditions, thus producing a tremendous amount of energy.

In the vast majority of the world's nuclear power plants, heat energy generated by burning uranium fuel is collected in ordinary water and is carried away from the reactor's core either as steam in boiling water reactors or as superheated water in pressurized-water reactors. In a pressurized-water reactor, the superheated water in the primary cooling loop is used to transfer heat energy to a secondary loop for the creation of steam. In either a boiling-water or pressurized-water installation, steam under high pressure is the medium used to transfer the nuclear reactor's heat energy to a turbine that mechanically turns a dynamo- electric machine, or electric generator. Boiling-water and pressurized-water reactors are called light-water reactors, because they utilize ordinary water to transfer the heat energy from reactor to turbine in the electricity generation process. In other reactor designs, the heat energy is transferred by pressurized heavy water, gas, or another cooling substance.

Nuclear Waste

The spent fuel rods are usually stored in water, which provides both cooling (the spent fuel continues to generate heat as a result of residual radioactive decay) and shielding (to protect the environment from residual ionizing radiation). A current concern in the nuclear power field is the safe disposal and isolation of either spent fuel from reactors or, if the reprocessing option is used, wastes from reprocessing plants.

These materials must be isolated from the biosphere until the radioactivity contained in them has diminished to a safe level. To put in perspective this period until radiation has been reduced to a safe level, the US Environmental Protection Agency has established a time standard for the Yucca Mountain Radioactive Waste storage facility of 10,000 to 1 million years.

Changing View

As fears of global warming have grown and both the safety and efficiency of nuclear power plants has improved, even leaders of the environmental community have taken a more positive view on the prospects of nuclear fueled energy. As pointed out by Greenpeace founder Patrick Moore, "more than 600 coal-fired electric plants in the United States produce 36 percent of U.S. emissions -- or nearly 10 percent of global emissions -- of carbon dioxide, the primary greenhouse gas responsible for climate change."

Fusion

In a fusion reaction, large amounts of energy are released when the nuclei of two light atoms (deuterium and tritium) fuse together to form a heavier one, helium. Tapping into this energy source offers the prospect of a long-term, safe, environmentally friendly option to meet the energy needs of a growing world population. There are numerous organizations involved with fusion technology.

Fusion is a particularly attractive energy solution as it uses a fuel that is abundant and available everywhere. The primary fuels used in fusion are deuterium and lithium. Deuterium is a hydrogen isotope, which can be readily extracted from water (there is around 30g of deuterium in every cubic metre of water), and lithium is an abundant light metal from which tritium can be generated inside the reactor.

Comparison of the amount of fuel to generate the same amount of energy

Research has not resulted in the construction of fusion power plant that produces useful energy. The nations of the earth have been engaged in this research effort for about 50 years. Fusion is arguably one of the major research challenges of the 21st Century.

Fusion is an option to provide environmentally benign energy for the future without depleting natural resources for next generations. One approach is called inertial confinement fusion which is the subject of research at the University of California. Another approach is magnetic confinement fusion. Fusion scientists from the European Union, China, India, Japan, Korea, Russia and the United States are now ready to proceed to the construction of a 500-MW (thermal power) experimental plant (ITER). Although further R&D work needs to be done on materials and on concept improvements ITER is expected to be the last major step between today's experiments and a demonstration power plant.