Mostly uranium-235, also plutonium
In the sun it is just protons, which are hydrogen nuclei. On earth experiments are using two isotopes of hydrogen, deuterium and tritium. These are still the same element, hydrogen, just two different isotopes.
It can be used to generate power but it is very dangerous yet little nuclear energy can generate ALOT of power.
Uranium is needed for nuclear power plants. Cesium, germanium, and radium are used in nuclear medicine. Strontium and plutonium are two more nuclear isotopes (elements).
The use of nuclear power
Yes, nuclear submarines generate nuclear power. There is a nuclear reactor on board (hence the tern nuclear submarine) which creates steam to drive the main engines to turn the screw(s).
Nuclear power is the cheapest, safest, and most efficient way to generate power. there are breeder reactors that generate free power by creating fissile material from the normal nuclear waste. so, it does not generate waste
First of all, you should distinguish between isotopes, not elements. For example, U-235 (uranium 235) and U-238 are the same element, and have the same chemical properties, but for a power plant, they are completely different things. U-235 is often used; it is also possible to convert other isotopes, such as U-238, into isotopes that are useful for nuclear fission - in this example, a plutonium isotope.
The energy released when a nuclear power plant generates heat to generate steam to generate electricity. The energy released when a nuclear weapon detonates.
Nuclear power is used to create large amounts of heat which generate steam. Basically, the steam is then used to spin steam turbines attached to generator sets, which generate power.
A nuclear power plant uses a slow, controlled nuclear chain reaction to heat water and generate electricity. A nuclear bomb uses a very rapid uncontrolled nuclear chain reaction in order to generate a massive explosion.
Unstable isotopes , mining ,refining of plutonium and thorium, production and explosion of nuclear weapons, nuclear power plants and fuels and preparation of radioactive isotopes.
The use of nuclear energy in civilian society is to generate electricity. In the military it is to make bombs (and hopefully not use them). There are also some uses in medicine where radio isotopes can be used for diagnosis and treatment. These isotopes are produced by irradiation in low power reactors which enable short lived radio isotopes to be obtained as required.