Radioisotopes for many uses (e.g. medical, industrial, scientific) are produced in nuclear reactors.
In some reactors it is, depends on the design.
The most common coolant used in nuclear reactors is water. There are light water reactors (using "regular" water), and the heavy water kind of reactor.
It is Uranium
Plutonium is used as nuclear fuel for nuclear reactors. Plutonium isotopes (239, 241) are fissionable with thermal neutrons releasing an extremely great quantity of energy.
Well, as nuclear reactors are nuclear reactors, nuclear reactors are not used inside nuclear reactors.
Current nuclear reactors rely on nuclear fission as their nuclear reaction.
We use nuclear fission in nuclear reactors to tap nuclear energy.
No, at least not for power reactors
If you are talking about the Nuclear Reactors in Japan, they were damaged because when they lost power, the water pumps used to cool them stopped, and all of the nuclear material overheated.
There may be Radium, Thorium, Uranium or even Plutonium which can be used in nuclear reactors.
Sea water is used to cool nuclear reactors in emergency situations when fresh water is not available. We usually find very pure water used in nuclear reactors as a primary coolant. This water stays quite pure and retains little radiation after shutdown and cooldown. But if an emergency situation arises and the "regular" primary coolant (the fresh water) is lost, it must be replaced with any water to cool the reactor. Sea water is better than nothing.
No substitute for nuclear power reactors especially if there is no available fossil fuel.
Nuclear reactors and nuclear weapons
No, nuclear fission operates all nuclear reactors. If they are power plant reactors it is used to generate electricity.
Nuclear reactors.
In test reactors.