To be fair the two are rather different. A nuclear reactor works by fission. That is the rough splitting in two of an atom when it absorbs a neutron from a neutron emitting source. Depending upon the number of neutrons released and absorbed the rate of energy released can be almost zero with no neutrons being added to Hiroshima or Nagasaki levels when neutrons and a dense mass of uranium in one spot are targeted. Even an uncontrolled event as in Chernobyl only results in a meltdown because of distances and purity of the nuclear material. At any rate those reactions are all much faster, and release more energy than that of nuclear decay. U238 will decay to Pb206. A difference of 32 nucleons. Where nuclear fission results in the atom splitting roughly in half to an average weight nucleus of 118. You can see that would be much further down the chart and much closer to iron on this chart"
View attachment 85107
Pb206 would be slightly below 8Mev on the chart and fission would be at about 8.5 on that chart. with U235 close to 7.5. Nuclear fission would ideally occur over a period of decades where and have a binding energy per nucleon change of about 1 where radioactive decay would take billions of years and have a change of energy of only .5Mev. It is a bit like comparing evolution and abiogenesis. With the exception that it is a far simpler process and is very very well understood. For both.