At night, the demand for electricity supplied by a fission nuclear reactor decreases. How is the fission nuclear reaction controlled to avoid overproduction of electricity? The temperature of the reactor is lowered because high temperature and pressure are needed. The temperature of the reactor is raised because the reaction slows down at higher temperatures. The exposure between the fuel rods and a neutron-absorbing material is increased. The exposure between the fuel rods and a neutron-absorbing material is reduced.