Heat energy in fission reactions.

[Infrasound]

Where does most of the heat energy in fission reactions come from?

-Does it come from radiation emitted from particles leaving the nucleus?
-Does it come from those actual particles leaving the nucleus and hitting surrounding gases in the air, causing them to move and heat up?
-Something else?

 

[QuantumPion]

Most of the heat energy created by fission comes from the kinetic energy of the fission fragments (~97%). When a Uranium atom splits, the two pieces go flying off at very high speeds. They bounce into their neighboring atoms, giving them energy, and so forth. The increased movement of the atoms is heat.

In addition, some of the energy is carried away by the free neutrons released by fission, which travel some distance through the reactor. For example, in a light water reactor, these neutrons will leave the fuel and bounce around the water molecules in the coolant and lose most of their energy there.

On top of that, there are also gammas and betas which are released as secondary radiation, as well as neutrinos (these pass through the whole reactor and probably the rest of the Earth without interacting with anything). But these are a small amount compared to the fission fragment kinetic energy.