In order to adequately control a chain reaction, it is necessary to have within the fissionable material a nonfissionable material. How does this material interact with neutrons

The non-fissile material, used in nuclear fission reactors, are able to absorb excess neutrons without undergoing fission itself. An example of these materials is Boron, Cadmium, and Indium used to make control rods. They control the number of neutrons in the nuclear reactor at any given moment hence consequently controlling the number of the nuclear chain reactions. This ensures the reactor's energy output can be controlled and also for safety reason so that the reactor does not overheat and explode.