The pressurised water reactor (PWR)
The term reactor refers to a structure in which material can be made to undergo a controlled nuclear reaction. They are used widely in industrial plants.
That released by fission in a nuclear reactor
Most often, light water (H2O) is used as a moderator in a nuclear reactor. Sometimes, heavy water (D2O), or graphite is used.
Not a nuclear reactor!
In most reactors in the world, water is used to absorb heat released from the reactor.
Uranium is the most common.
That released by fission in a nuclear reactor
This is used in the nuclear reactor that is known as Boiling Water Reactor (BWR) in which heat produced by the nuclear fission in the nuclear fuel allows the light water reactor coolant to boil. Then, the nuclear reactor moisture separator is used to increase the dryness of the produced steam before it goes to the reactor steam turbines.
Yes, they are widely used for data gathering and display to the operators, also for reactor simulators, and assessment of the physics state of the reactor and its fuel cycling requirements.
Never a nuclear reactor is used in airplanes. However, it is used in submarines.
Boron is used inside a nuclear reactor inside a control rod which is used to 'soak' up the neutrons inside the nuclear reactor, a control rod can be used to control the rate of fission inside a nuclear reactor.
Uranium and most transuranic elements. Plutonium and Americium are particularly good reactor fuels.