RAS question
What is the role of control rods in a nuclear reactor?
Correct answer: (D) Absorb neutrons to control the fission rate.
Control rods in a nuclear reactor absorb neutrons in the reactor core to control the rate of fission and, therefore, reactor power.
Explanation
Control rods are the reactor's main way of controlling the fission chain reaction. The IAEA ARIS glossary defines a control rod as a rod, plate or tube used to absorb neutrons in the reactor core, helping control the number of fission events and the reactor's power. That is why inserting control rods slows the reaction and reduces power, while withdrawing them allows more neutrons to sustain fission and raises power. The usual absorber materials are boron, cadmium or hafnium, and the emergency logic is that in a SCRAM, all rods are fully inserted so neutron absorption rapidly shuts the reactor down.
Why the other options are wrong
- (A) Electricity is not produced directly by control rods; in a nuclear power plant, heat from the reactor is used to drive the turbine-generator system.
- (B) Cooling is the job of the coolant, whereas control rods regulate the reaction by absorbing neutrons in the core.
- (C) Heat comes from fission in the nuclear fuel, while control rods limit that process by reducing the neutrons available for further fission.
Concept
This tests the basic nuclear-reactor components part of Science and Technology: fuel, coolant, moderator and control rods have distinct functions. RAS repeatedly asks such component-function questions because they check conceptual clarity rather than memorised reactor names.