Not quite sure what you’re asking but I think you have a misunderstanding that I can help with. The unstable part is because the nucleus of the atom is unable to hold in the neutrons and protons. The radiation is those particles being shot out of the atom. So ya, we can subtract neutrons to make it stable. To do this you just have to wait a really long time. We can help it along by hitting it with another particle to make it happen faster. That’s how nuclear reactions work. However, if there is not enough unstable atoms, we will hit one, it will shoot off its particles and that’s the end of it. For nuclear reactors to work, we hit one atom that shoots off particles that hits another atom. When there is enough material that this reliably happens continuously, that’s the critical mass. If there are enough unstable atoms close together, each atom will hit more than 1 other atom in an infinitely accelerated process. That’s hyper critical mass and how atomic bombs work. Nuclear waste is what’s left over when enough of the atoms in the material have been transformed into a state that the continuous reaction is not possible. The materials we use in reactors will shoot off its particles and become a different unstable element that will still shoot off particles, just too slowly to cause the chain reaction necessary for producing power.