What initiates the fission process in nuclear reactors?

The fission process in nuclear reactors is initiated when a neutron strikes a Uranium atom. This event is crucial because uranium isotopes, particularly Uranium-235, have a nucleus that can be split when it absorbs a neutron. Upon the neutron's impact, the Uranium nucleus becomes unstable and undergoes fission, splitting into two smaller nuclei and releasing a significant amount of energy, along with additional neutrons. These newly released neutrons can then go on to strike other Uranium atoms, creating a chain reaction that is essential for sustaining energy production in the reactor.

In contrast, protons do not initiate fission as they are positively charged and would repel the positively charged nucleus of a Uranium atom, making it highly unlikely for them to induce fission. Heat generated from previous fissions does not initiate the next fission event; instead, it is a byproduct of the reaction that contributes to the reactor's overall temperature and pressure management. A chemical reaction with water would not initiate fission either, as water's role in a nuclear reactor is primarily as a coolant and neutron moderator, not as an initiator of fission.