 fission is a nuclear reaction in which a large nucleus splits an example copy if we have uranium 235 if that uranium is hit by a neutron at the right speed then it will temporarily become uranium 236 and then split into two chucks and some additional neutrons that will fly off so the chunks could be krypton 92 and barium 141 if I was to write down the nuclear reaction for this it would be that one neutron plus uranium 235 92 will become one krypton 92 plus barium 141 6 plus 3 neutrons now as with all nuclear reactions the total best number on the top is conserved so we have 235 plus 1 is 236 so we should have 92 plus 141 plus 3 times 1 should give us the same number this is by the way how if you have a question where only one of the products is given you can figure out the mass number of the other one you know that the top lines here must add up same happens for the total charge or the atomic number so zero protons here 92 protons here 36 here 56 here everything here together should be equal to everything here together what is not conserved is the mass the mass as in all nuclear reaction or some of the mass is converted into energy which makes free efficient so efficient in producing energy in efficient power plant we need very little fuel of which some of the mass is converted to energy C is the speed of light very large number so C squared so we get a lot of energy out of a very little mass so we need not a lot of fuel in our reactor to make this happen the problem in the nuclear reactor is actually that some of the products of the reactions are radioactive so the waste of the reactor is actually dangerous and has to be put away safely so it cannot harm anyone the atomic bomb was also built based on the fission principle basically what's happening in the atomic bomb is you put some isotope that can easily split so densely together so that the nutrients that fly off themselves can hit other isotopes and create a chain reaction so you get more and more and more and then you get a lot of energy released in one shot and the thing explodes this is of course exactly what you try to avoid in a nuclear reactor where you try to control how many nutrients are able to hit other isotopes that could split so that you don't get a chain reaction that gets out of control you want to control it there was also a case of a natural nuclear reactor in Gabon Africa where there was enough uranium close enough together so that there was a chain reaction going on where the nutrients that got out of one reaction were able to hit other isotopes