Editing Scram (section)

===Decay heat===
{{Further|Decay heat}}
Not all of the heat in a nuclear reactor is generated by the chain reaction that a scram is designed to stop. For a reactor that is scrammed after holding a constant power level for an extended period (greater than 100 hrs), about 7% of the steady-state power will remain after initial shutdown due to fission product decay that cannot be stopped. For a reactor that has not had a constant power history, the exact percentage is determined by the concentrations and half-lives of the individual fission products in the core at the time of the scram.

The power produced by [[decay heat]] decreases as the fission products decay, but it is large enough that failure to remove decay heat may cause the reactor core temperature to rise to dangerous levels and has caused [[nuclear accidents]], including the nuclear accidents at [[Three Mile Island accident|Three Mile Island]] and [[Fukushima I nuclear accidents|Fukushima I]].