I wonder if someone could help me out. I'm a bit confused about how fusion (and fission for that matter) releases energy. Looking at a graph of binding energy per nucleon against mass number, fusion gives out energy up to iron (correct?). The thing that confuses me is that as two nuclei are fused to make a heavier nuclei, the binding energy per nucleon INCREASES. So if the binding energy of the product is greater than the binding energy of the two original nuclei, would that not require energy rather than release energy? So for example if there is more binding energy in a helium nucleus than in a dueterium nucleus and a tritum nucleus, energy energy would need to be input to increase that binding energy. So i'm not sure where i've gone wrong. It is probably very obvious to you, so please help!