is it possible to use nuclear material as fuel for rockets? If possible, would be more effective to use this as a source of fuel for launching space craft into space and in space as well?

I've had this thought about NASA and their rockets for a bit. Is it possible to use uranium, plutonium, or other nuclear material as fuel for a rocket to push a space craft? Would it be more effective than the fuel they use now since nuclear reactions can cause a massive release of energy? 

Is it possible to use nuclear material and have a reaction where it is released in small amounts. Like a bomb but instead of having the entire thing go off, only small amounts goes off. 
Nuclear thermal rockets (NTRs) are thermal rockets that use the heat from a nuclear reaction to replace the chemical energy of propellants [4]. A liquid propellant, usually hydrogen, is pumped through a reactor core where uranium atoms split apart and release heat through fission [2]. This heat is transferred to the hydrogen which then expands through a rocket nozzle to create thrust [4]. NTRs are more energy dense and twice as efficient as chemical rockets [3]. This means that they can create more thrust from a given amount of propellant, which is a measure of performance known as specific impulse [3]. They also have the benefit of not producing any exhaust gases, which makes them very attractive for use in space [5].
It is possible to use nuclear material to power rockets but there are two types of nuclear rocket propulsion systems. [1][2][3]  The first is called nuclear thermal propulsion. These systems are very powerful and moderately efficient. They use a small nuclear fission reactor – similar to those found in nuclear submarines – to heat a gas, such as hydrogen, and that gas is then accelerated through a rocket nozzle to provide thrust.  Engineers from NASA estimate that a mission to Mars powered by nuclear thermal propulsion would be 20%-25% shorter than a trip on a chemical-powered rocket. [1]  The second nuclear-based rocket system is called nuclear electric propulsion. No nuclear electric systems have been built yet, but the idea is to use a high-power fission reactor to generate electricity that would then power an electrical propulsion system like a Hall thruster. This would be very efficient, about three times better than a nuclear thermal propulsion system. Since the nuclear reactor could create a lot of power, many individual electric thrusters could be operated simultaneously to generate a good amount of thrust. [3]