One of the major requirements for sustaining human progress is an adequate source of energy. The current largest sources of energy are the combustion of coal, oil and natural gas. They will last quite a while but will probably run out or become harmful in tens to hundreds of years. Solar energy will also work but is not much developed yet except for special applications because of its high cost. This high cost as a main source, e.g. for central station electricity, is likely to continue, and nuclear energy is likely to remain cheaper. A major advantage of nuclear energy (and also of solar energy) is that it doesn't put carbon dioxide (CO2) into the atmosphere. How much of an advantage depends on how bad the CO2 problem turns out to be. In this concern, although nuclear technology is mainly used for the production of electricity in nuclear power plants, this is not the only utility that can be given.