Describe what happens in a fission reaction. what is a commonly used isotope in a nuclear fission reactor? describe how a fission nuclear reactor power plant works.

Answer 1: 
Nuclear fission splitting of the nucleus of an atom into two or more smaller nuclei. Smaller nuclei generated during nuclear fission reaction are called fission products.Nuclear fission reaction is an exothermic process. It releases enormous amount of heat.

Answer 2:
The two most common isotopes used in nuclear fission reactor are Uranium-235 and Plutonium-239. However, Uranium-235 is the preferred isotope for nuclear fission reactor

Answer 3:
Nuclear fission reactors are designed such that they can sustain chain reaction. They employed U-235 as a solid fuel, which is surrounded by water. The water acts are coolant, which helps to maintain temperature of nuclear reactor. When the reactor is in operation, U-235 breaks down into smaller atoms, During this process neutrons and heat is released. These neutrons will collide other uranium atom causing its fission. This process will continue further, thereby more neutrons and heat.