Question

Which of the following are used as control rods in a nuclear reactor?
A.Cadmium rods
B.Graphite rods
C.Steel rods
D.All of these

Answer 1

Hint:We have to know that control rods are used in nuclear reactors to maintain the rate of fission of uranium or plutonium. Their compositions contain chemical elements like boron, silver, or indium, which have the ability to absorb several neutrons without fissioning themselves. Boron is a common neutron absorber.

Complete answer:
We know that the fission rate of plutonium (or) uranium is controlled by control rods. Controls rods are usually made of chemical elements like cadmium, boron, indium (or) silver. Compounds (or) alloys like high-boron steel, zirconium diboride, and titanium diboride. These elements have the ability to several neutrons without fissioning themselves. These elements contain various neutron capture cross sections for neutrons of different energies.
Control rods are inserted into the core of a nuclear reactor and are adjusted to regulate the rate of the nuclear chain reaction. The number of control rods inserted, and the distance at which they are inserted, influences the reactivity of the reactor. Control rods are partially removed from the core to permit the nuclear chain reaction to begin up and rise to the desired power level.
We can use cadmium rods as control rods because they have the ability to absorb neutrons without fissioning themselves.
Therefore, the option (A) is correct.

Note: We have to know that based on the energy spectrum of its neutrons, the design of each reactor could use different materials for control rod. Some other elements that could be used as control rods are boron, hafnium, samarium, terbium, erbium, thulium, ytterbium, and lutetium. Generally, certain rare-earth elements are excellent neutron absorbers.