The first reactor in 1942 was supervised by Enrico Fermi
Sir James Chadwick discovered it in 1932
Martin Klaproth did not discover nuclear energy, he discovered the atoms uranium, zirconium, and cerium. The discovery of nuclear energy is credited to several people, including Albert Einstein and Marie Curie.
The first law of thermodynamics states that energy can be transformed, but not created nor destroyed. In a nuclear reaction, mass is transformed into energy.
Nuclear energy is first changed to heat in a nuclear power plant using a process called nuclear fission. The heat generated is then used to produce steam, which drives turbines to generate electricity.
Henri Becquerel discovered in 1896 the natural radioactivity.
The first use of nuclear energy before electricity was in the form of nuclear weapons, such as the atomic bombs dropped on Hiroshima and Nagasaki during World War II in 1945.
nobody knows
United States in a bomb!
You could extend this question to ask "why is the world using nuclear energy"? The answer is simply because - we are running out of resources to create energy. Coal, gas and oil are running low. Renewable sources such as wind, geothermal, solar and hydro do not produce enough to cover all of the population. The answer, for now until we discover new means of harvesting energy is nuclear.
This was part of the WW2 Manhattan Project to develop the A-bomb. The first nuclear reactor was demonstrated in Chicago in 1942
Nuclear fusion produces nuclear energy