How  is nuclear energy generated ?  

 There is only one major difference between operating a thermal power plant and a nuclear power plant. The single difference lies in the type of fuel. both types of power plants heat water to produce. Pressurized  steam which turns turbines  that generate electricity. A thermal power plant uses coal as the Fuel, which a nuclear reactor uses uranium  coal is ready for use immediately  after mining. In contrast, Uranium has to undergo a further step for it to become a suitable fuel. Naturally mined uranium has 99.3 percent of U-238, 0.7 percent of U-235and less than 0.01 percent of u-234, all of these being Isotopes of uranium. U-235 is unstable and decays to gain stability .In the process, it releases energy. It Can also undergo Induced fission, which is done by firing free neutrons at the nucleus, which is what Most reactors do to generate energy. But to start a nuclear reaction the proportion of U-235 should be Higher than its natural form. Reactor's  fuel has about 4 to 5 percent of U-235. The process of Increasing the proportion of fissionable uranium in the sample is called enrichment. this can be done by A gaseous diffusion  gas centrifuge and laser separation, of these, the first two are generally  used by reactors. U-238 can also be used as a fuel in breeder reactors.

However, The process of using U-238 is mere advanced and hence, it is less preferred as fuel compared  to the other two.