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?

When electricity demand decreases, the reactor’s fission rate must be reduced. Increasing the exposure of the fuel rods to neutron-absorbing material means more neutrons are absorbed, so fewer neutrons trigger further fissions and the chain reaction slows. Thus, the correct choice is increasing exposure to neutron-absorbing material.

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