| Splitting more than hairs
Nuclear energy is energy derived from the forces binding the nuclei of atoms. The primary earthly uses of nuclear energy are electricity generation, known as nuclear power, and spectacularly powerful explosives which can be used for
obliterating entire nations deterring military action, known as a nuclear bomb.
Different nuclei have different binding energies. Because they are generally very large, a reaction that changes one type of nucleus into another releases tremendous amounts of energy, millions of times more than the most energetic chemical reactions. The only problem is that to react, the nuclei need to come very close to each other. This requires either extremely high temperature and density, acceleration to very high speeds, or the use of neutrons.
 Types of nuclear energy
The curve of binding energy (see picture below) has a maximum for elements with medium atomic weights. It reaches the maximum for iron-56, which is the most stable nuclide in the universe and forms the cores of massive burnt out stars. This means we can theoretically extract nuclear energy from any element other than iron. In practice, it is feasible for three cases:
- Heavier elements can be synthesized out of lighter ones. Specifically by:
- Nuclear fusion -- The process that makes the Sun shine. Its most practical variant on Earth involves reacting two rare hydrogen isotopes, deuterium and tritium, to yield helium and a neutron. This process is used in practice in thermonuclear bombs, an extremely powerful type of nuclear bomb. To use it to generate electricity presents massive engineering challenges, but research is progressing at a reasonable rate.
- Heavy elements can break up or be broken up into lighter fragments:
- Nuclear fission -- The process of bombarding certain elements, such as uranium and thorium, with neutrons. This causes their nuclei to become very unstable and break up into fragments of varying size. Some new neutrons are released in the reaction, so it can be carried out in a self-sustaining fashion (a chain reaction). Fission of uranium-235 is the source of energy for almost all nuclear power stations, as well as nuclear-powered submarines and aircraft carriers. Fission of plutonium-239 (bred by irradiating uranium-238 with neutrons) is the source of energy for most nuclear bombs. Another potential nuclear energy method is irradiating thorium-232 (the only thorium isotope to occur naturally in earth's crust in appreciable quantities) with neutrons to produce uranium-233 which could then be used as core-fuel in a nuclear reactor, particularly one that uses molten salts as the fuel carrier.
- Radioactive decay -- Some heavy elements will also break down into smaller fragments spontaneously over time. For some artificial isotopes this process yields enough power to be practically useful. However, the power of a radioactive decay-powered device cannot be regulated, and decreases logarithmically over time. The most common use of this variant is the radioisotope thermoelectric generator (RTG), a type of "nuclear battery". It is used to provide a power source for the entire lifetime of a device which would be prohibitively expensive or impossible to refuel, such as deep space probes or navigation beacons in remote locations.
 What it can do
Here are some things nuclear energy has done in the past, and remains capable of doing in the present. To a person living a century ago, this list would look entirely magical. This is an example of Clarke's third law.
- Provide concentrated, carbon-dioxide emissions-free electricity on demand, with little regard to geography and weather. Just don't build on a fault line.
- Propel a ship for many years without the need for refueling.
- Power a spacecraft far from the Sun so we can learn more about the outer reaches of the Solar System.
- Raze a large city to the ground in a few seconds.
- Fundamentally change the geopolitics of the 20th century.
- Seal blown-out gas wells.
- Cause earthquakes.
- Achieve transmutation - the "holy grail" of alchemy.
 Why some people do not like it
Nuclear energy was the central instrument of geopolitics during the Cold War. Both rival and openly hostile superpowers, the United States and the Soviet Union, had a large arsenal of nuclear weapons and held each other in a stalemate. Neither could strike first, because the other side would quickly launch a retaliation, resulting in global destruction. This situation is known as mutually assured destruction. While the resulting standoff turned out to be surprisingly stable and prevented any open armed conflict from occurring between the superpowers, the threat of man-made Armageddon was something completely unprecedented in history. A powerful anti-nuclear movement intent on achieving nuclear disarmament was formed. It was successful in effectively banning nuclear explosions for any purposes.
Unfortunately, the fuss with nuclear weapons caused the very word "nuclear" to carry a connotation of danger, evil and death. To this day it causes a lot of animosity towards peaceful uses of nuclear energy, especially nuclear power.
Nuclear power (most especially fission) has been the subject of much controversy over the nearly 70 years that it has been studied and used; while the process of using nuclear-fired electricity generators is fairly clean, the technology of fission reactors is sometimes prone to problems. Although waste is small in volume (compared to most industries), safe waste disposal is a tremendous problem, demanding answers that will allow the waste to stay stored for tens of thousands of years - substantially longer than all of current recorded history. A proposed waste-storage facility at Yucca Mountain has yet to be built, and few new reactors have been built in the US in recent decades.
Spent fuel can be reprocessed to extract fissionable material, but this raises security and proliferation concerns; much reprocessed uranium fuel is plutonium-239 created during the fission process, which is far more readily useful for building small nuclear weapons than uranium (it is also harder to fission plutonium-239 in a thermal-spectrum reactor feasibly than it is to fission uranium-235 or uranium-233 in a thermal-spectrum reactor; for this reason, most reactors that consume plutonium-239 are fast-spectrum reactors, which tend more towards having a "twitchy" control response than most thermal-spectrum reactors). Even with fuel reprocessing, however, the problem of disposal of support materials (contaminated gear and the like) remains.
In the United States, new construction licenses were not granted for 33 years after the Three Mile Island accident wiped out half the power generation capacity of a Pennsylvania plant in 1979. However, some plants which obtained construction licenses earlier or were mothballed in a partially constructed state for a long time were completed in this period, notably Seabrook-I in New Hampshire - Seabrook-II was abandoned. The first new construction permit since then was granted at the beginning of 2012. The sentiment towards nuclear energy has a lot of regional variation. Several European nations, such as Austria and Germany, have taken radical anti-nuclear positions, with Austria completely banning civilian nuclear power. Meanwhile, France gets more than three quarters of its electricity from nuclear reactors.
- ↑ Low and medium-mass stars like our Sun cannot fuse beyond carbon and oxygen
- ↑ When the Cassini probe was launched, there were protests over the fact that it contained some 68 pounds of plutonium. Some even worried that the plutonium could be stolen and used to make atomic bombs. Such fears were groundless; RTGs use plutonium-238, an isotope that's useless for making nuclear weapons.
- ↑ According to this old Soviet film, anyhow
- ↑ Specifically, it can turn an isotope of mercury into gold, but this is not economical. Extracting precious metals from nuclear waste is a more promising idea. See the Wikipedia article on Synthesis of precious metals.
- ↑ For example, a medical procedure known as "nuclear magnetic resonance" was renamed to "magnetic resonance imaging" specifically to avoid the use of the word "nuclear". The same technique used in analytical chemistry retains the original name, as it doesn't need to be sold to the general public.
- ↑ Windscale, Three Mile Island, Chernobyl, Fukushima, and many rather less severe incidents that don't get a lot of play.
- ↑ World Nuclear News: Approval for first nuclear new build in America
- ↑ http://www.world-nuclear.org/information-library/country-profiles/countries-a-f/france.aspx Nuclear Power in France