No, at least not for power reactors
No, but experiments with lasers to produce nuclear fusionare being conducted, and this technique may be used sometime in the future in a fusion nuclear reactor.
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.
There may be Radium, Thorium, Uranium or even Plutonium which can be used in nuclear reactors.
Helium is used in balloons, leak testing, welding in controlled atmospheres, magnetic resonance imaging, cooling agent for nuclear reactors, lasers, etc.
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.
Radioisotopes for many uses (e.g. medical, industrial, scientific) are produced in nuclear reactors.