[claypool1]

There is no lost matter, the fission products account for most. Alpha radiation particles are basically helium atoms without any electrons, very heavy, and the rest is released as electrons, positrons, neutrons, and protons. There is no lost matter, it's all there fission does not break the laws of physics.

[rerevisionist]

Claypool1, the whole mystique of nuclear weapons is the idea that e=mc squared. There's supposed to be interconvertibility between mass and energy. All the calculations I've seen suppose there's a loss of mass, with energy released as per that formula. This is supposed to be a 'law of physics'.

If you take the view that 'nuclear energy' is simply energy released by rearranging particles in a nucleus, this is a different matter. Normal fires etc are supposed to involve only the electron arrangements, so that for example carbon on burning ends up with its electrons tangled up with those from oxygen atoms. It's a reasonable guess that nuclear rearrangements might generate more energy, but the amount could only be determined by experiment, or by accurate knowledge of the nucleus. They might turn out to be much less than the famous equation.

You seem unsure as to what the 'laws of physics' are believed to be.

[FirstClassSkeptic]

There is no lost matter,

That's what I think: There is no matter to energy conversion. At least, I can't see it proven in any experiment.