The kind of energy that is released is called NUCLEAR ENERGY.
Nuclear energy refers to the energy that is released from a radioactive element as a result of decay of the nucleus of that element. An atom is made up of three sub particles, which are proton, neutron and electrons. The proton and the neutron are located in the nucleus of the element while the electron is located at the outside of the nucleus. Radioactive elements usually undergo spontaneous decay and during the process a lot of energy is released, this energy is called nuclear energy because it comes from the decay of the nucleus of the atom of the element. Nuclear energy can be obtained as a result of nuclear fusion or nuclear fission and the energy can be used to do a lot of things such as generation of electricity.