[dontwearitout]

The energy of neutrons isn't really analogous to the energy of atoms in chemical reactions, but absolutely affects the reaction dynamics. The "cross section", or interaction probability, is a strong function of neutron speed. In bombs the neutrons don't get a chance to slow down, but in reactors you try to reduce them to "room temperature" speeds using collisions with light, inert nuclei (the moderator). Here's a diagram showing the interaction probability vs. neutron speed for a few isotopes of uranium: https://tinyurl.com/u235-cross-section