What are the fuels used to produce nuclear energy?
Naturally occurring uranium contains 0.71% of the isotope U -235, the rest mainly being the isotope U -238. Of all the naturally occurring materials only the rare isotope U -235 can sustain а fission chain reaction and is called fissile material. Other fissile materials, which can fuel nuclear reactors, are plutonium and U -233. These latter materials are man-made and do not occur in nature. Plutonium is created when U -238 is irradiated in а nuclear reactor where it absorbs neutrons which transmutes а part of the U -238 into plutonium. Similarly, U -233 is created when thorium is irradiated in а nuclear reactor, where it absorbs neutrons, which transmutes а part of the thorium into U-233. Thus U-238 and thorium are also valuable nuclear resources, called fertile materials, as they can be converted into fissile material for fuelling nuclear reactors and producing energy.
