Reply #37: You are 100% wrong. Nuclear decay in aggregate produces 200 billion times as much heat.

[Statistical]

SF events are very rare. Larger amount or not it produces negligible energy. Period. This is physics 101.

"Fission events release fifty times as much energy as decay events"
Yeah but 1 fission event vs trillion decay events. Which produces more energy. SF is very rare.

For each decay of U-235 http://en.wikipedia.org/wiki/Spontaneous_fission

0.000000007% of the time it will result in SF.
99.999999993% of the time it will result in decay.

So we even though fission produces 50x the energy it occurs one 14 trillionth as often so it produces negligble energy.

Come on I can't explain it an simpler than this:
Spontaneous Fission - 50x the energy. occurs 1/14 trillionth as often
Nuclear Decay - 1/50th the energy. occurs 14 trillion times as often.

SF produces a rounding error of energy. We can say that with absolute certainty. There is no mechanism to change the rate of SF either intentionally or not. You can't make it happen more often. Virtually all the heat from spent fuel comes from nuclear decay.

What makes fission powerful (in nuclear weapons and nuclear power) is the chain reaction. The ability to wait for a spontaneous fission to occur and use that neutron to FORCE a fission and use that neutron to FORCE two more fissions, etc. The Spontaneous fission is simply the "trigger". Without the chain reaction a nuclear reactor couldn't warm a cup of tea.