I'm fairly new to nuclear engineering. Basically two questions regarding nuclear fission. 1) Neutrons hit atomic nuclei of fuel in reactor which in turn causes atoms to decay until a stable atomic isotope is ultimately reached. However, surely the "stable" isotopes (and also those unstable isotopes which are now decaying) are themselves bombarded with more neutrons causing further decay and so on until there is nothing left but energy?? Or is it dependent on the (kinetic) energy of neutrons being large enough to overcome the binding energies of nuclei to cause fission? In other words, if the neutron energies are not sufficiently strong enough, then the isotopes (stable and unstable) will not decay (further) as the atomic nuclei binding energies are greater than the neutron (kinetic) energies. Is this so? The cladding surrounding nuclear fuel (usually zirconium), and also the liquid metal coolant (for liquid metal reactors and either sodium or lead being used) presumably do not decay (due to neutron bombardment) because their respective atomic nuclei binding energies are greater than the energy of the neutrons? Is that so? 2) Presumably isotopes that do decay, decay into almost every possible combination of isotope down the line of decay so that there could be literally hundreds of reactions occurring at any one moment? If so, how is the total energy of all these reactions calculated to determine the outputs of reactors?