How is energy released in a nuclear reaction?

I'm fairly sure that it will lose energy in the form of radiation, wether that be apha, beta or gamma rays.

In a nuclear reaction the atoms of a heavy element divide to form two small atoms. This happens when the heavy atom gains energy. In a nuclear reactor a neutron is used to excite the atoms. The heavy atoms breaks to form two lighter atoms. But two neutrons are separated from the product, out of which one is converted to energy and the other is left.

Nuclear energy is produced within a nuclear reactor.This is a generator that has the amazing capacity to start, control and maintain a fission chain reaction.  
Within the reactor, the nuclei (that's just the plural of the word "nucleus," which is the center of an atom) of uranium atoms are split, which produces lots of heat, two lighter nuclei, several smaller fragments and a whole bunch of free neutrons.

The force of the impact causes these free neutrons to fly off in all the directions, millions of them colliding with a whole new bunch of uranium nuclei, which repeats the process once more. This never-ending sequence of splitting, flying and then splitting again is called a chain reaction.

The heat generated by the inter atomic nuclear chain reaction turns the water circulated on reactor by special piped network from huge reservoirs turns into steam, which then turns the hydro turbines to generate the electricity!

Once all this is done, the steam that left the turbine is cooled and converted back into water. This water cycles right back through the heat exchanger again, and the process repeats itself over and over and over !

Energy is a process which we observe  when a mass moves at a certain velocity.Therfore when a mass structure moves it is said to display Energy.
Mass is matter which is an entity having  a structure and volume.
Energy is not an entity which has a volume.
Therefore , we cannot say that Energy which has  no volume converts into an entity which has a volume and structure. And vice versa.

What is released in a nuclear reation is micromasses which move at the speed of light having the energy in accordance to  Henri Poincare's equation " E= m c^2". Where m is the sum of all micromasses released as a result of a nuclear reaction and C is the velocity of light.