Nuclear Power

Nuclear power is a type of nuclear technology involving the controlled use of nuclear fission to release energy for work including propulsion, heat, and the generation of electricity. Nuclear energy is produced by a controlled nuclear chain reaction and creates heat—which is used to boil water, produce steam, and drive a steam turbine. The turbine can be used for mechanical work and also to generate electricity.

As of 2004, nuclear power provided 6.5% of the world's energy and 15.7% of the world's electricity, with the U.S., France, and Japan together accounting for 57% of all nuclear generated electricity. As of 2007, the IAEA reported there are 435 nuclear power reactors in operation in the world, operating in 31 different countries.

The United States produces the most nuclear energy, with nuclear power providing 20% of the electricity it consumes, while France produces the highest percentage of its electrical energy from nuclear reactors—80% as of 2006. In the European Union as a whole, nuclear energy provides 30% of the electricity. Nuclear energy policy differs between European Union countries, and some, such as Austria and Ireland, have no active nuclear power stations. In comparison France has a large number of these plants, with 16 currently in use throughout the country.

Many military and some civilian (such as some icebreaker) ships use nuclear marine propulsion, a form of nuclear propulsion. International research is ongoing into different safety improvements such as passively safe plants, the use of nuclear fusion, and additional uses of produced heat such as the hydrogen production (in support of a hydrogen economy), for desalinating sea water, and for use in district heating systems.

History

Nuclear fission was first experimentally achieved by Enrico Fermi in 1934 when his team bombarded uranium with neutrons, however neither Fermi nor many others understood the results properly. In 1938, German chemists Otto Hahn and Fritz Strassmann, along with Austrian physicists Lise Meitner and Otto Robert Frisch, conducted experiments with the products of neutron-bombarded uranium. They determined that the nucleus of the massive uranium atoms had been split into two roughly equal pieces by the relatively tiny neutron, an almost incredible result. The recognition by numerous scientists (Leo Szilard being one of the first) that if the fission reactions released additional neutrons that they could be used to generate a self-sustaining nuclear chain reaction spurred scientists in many countries (including the United States, the United Kingdom, France, Germany, and the Soviet Union) to petition their government to support fission research.

In the United States, where Fermi and Szilard had both emigrated, this led to the creation of the first man-made reactor, known as Chicago Pile-1, which achieved criticality on December 2, 1942. This work became part of the Manhattan Project, which built giant reactors at Hanford, Washington in order to breed plutonium for use in the first nuclear weapons. (A parallel uranium enrichment effort was also pursued.)

After World War II, the fear that reactor research would encourage the rapid spread of nuclear weapons and nuclear "know-how", combined with what many scientists thought would be a long road of development, created a situation in which reactor research was kept under very strict government control and classification. Additionally, most reactor research centered on purely military purposes. Electricity was generated for the first time by a nuclear reactor on December 20, 1951 at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW (the Arco Reactor was also the first to experience partial meltdown, in 1955). In 1952, a report by the Paley Commission (The President's Materials Policy Commission) for President Harry Truman made a "relatively pessimistic" assessment of nuclear power, and called for "aggressive research in the whole field of solar energy". A December 1953 speech by President Dwight Eisenhower, "Atoms for Peace", emphasized the useful harnessing of the atom and set the U.S. on a course of strong government support for international use of nuclear power.

Nuclear reactor technology

Conventional thermal power plants all have a fuel source to provide heat. Examples are gas, coal, or oil. For a nuclear power plant, this heat is provided by nuclear fission inside the nuclear reactor. When a relatively large fissile atomic nucleus is struck by a neutron it forms two or more smaller nuclei as fission products, releasing energy and neutrons in a process called nuclear fission. The neutrons then trigger further fission. And so on. When this nuclear chain reaction is controlled, the energy released can be used to heat water, produce steam and drive a turbine that generates electricity. While a nuclear power plant uses the same fuel, uranium-235 or plutonium-239, a nuclear explosive involves an uncontrolled chain reaction, and the rate of fission in a reactor is not capable of reaching sufficient levels to trigger a nuclear explosion because commercial reactor grade nuclear fuel is not enriched to a high enough level. Naturally found uranium is less than 1% U-235, the rest being U-238. Most reactor fuel is enriched to only 3-4%, but some designs use natural uranium or highly enriched uranium. Reactors for nuclear submarines and large naval surface ships, such as aircraft carriers, commonly use highly enriched uranium. Although highly enriched uranium is more expensive, it reduces the frequency of refueling, which is very useful for military vessels. CANDU reactors are able to use unenriched uranium because the heavy water they use as a moderator and coolant does not absorb neutrons like light water does.

The chain reaction is controlled through the use of materials that absorb and moderate neutrons. In uranium-fueled reactors, neutrons must be moderated (slowed down) because slow neutrons are more likely to cause fission when colliding with a uranium-235 nucleus. Light water reactors use ordinary water to moderate and cool the reactors. When at operating temperatures if the temperature of the water increases, its density drops, and fewer neutrons passing through it are slowed enough to trigger further reactions. That negative feedback stabilizes the reaction rate.

A number of other designs for nuclear power generation, the Generation IV reactors, are the subject of active research and may be used for practical power generation in the future. A number of the advanced nuclear reactor designs could also make critical fission reactors much cleaner, much safer and/or much less of a risk to the proliferation of nuclear weapons.

Controlled nuclear fusion could in principle be used in fusion power plants to produce power without the complexities of handling actinides, but significant scientific and technical obstacles remain. Several fusion reactors have been built, but as yet none has 'produced' more thermal energy than electrical energy consumed. Despite research having started in the 1950s, no commercial fusion reactor is expected before 2050. The ITER project is currently leading the effort to commercialize fusion power.

Fuel resources

Uranium is a common element, approximately as common as tin or zinc, and it is a constituent of most rocks and of the sea. The world's present measured resources of uranium, economically recoverable at a price of 130 USD/kg, are enough to last for some 70 years at current consumption. This represents a higher level of assured resources than is normal for most minerals. On the basis of analogies with other metallic minerals, a doubling of price from present levels could be expected to create about a tenfold increase in measured resources, over time. The fuel's contribution to the overall cost of the electricity produced is relatively small, so even a large fuel price escalation will have relatively little effect on final price. For instance, typically a doubling of the uranium market price would increase the fuel cost for a light water reactor by 26% and the electricity cost about 7% (whereas doubling the gas price would typically add 70% to the price of electricity from that source). At higher prices eventually extraction from sources such as granite and seawater become economically feasible.

Current light water reactors make relatively inefficient use of nuclear fuel, leading to energy waste. But nuclear reprocessing makes this waste reusable (except in the USA, where this is not allowed) and more efficient reactor designs would allow better use of the available resources (and reduce the amount of waste material).

Fusion power commonly propose the use of deuterium, an isotope of hydrogen, as fuel and in many current designs also lithium. Assuming a fusion energy output equal to the current global output and that this does not increase in the future, then the known current lithium reserves would last 3000 years, lithium from sea water would last 60 million years, and a more complicated fusion process using only deuterium from sea water would have fuel for 150 billion years.