# Can nuclear reactions be controlled?

In a nuclear reactor, boron control rods are used to absorb the flow of neutrons that are given off by the radioactive decay of the ${U}^{235}$ and this prevents them from colliding with other atomic nuclei and continuing the chain reaction.
If all the neutrons given off by the ${U}^{235}$ are absorbed, then the reaction will stop completely until the control rods are removed from the reactor.