MCQ Detailed View

In nuclear reactors, the process of nuclear fission involves splitting heavy atomic nuclei such as uranium-235 or plutonium-239 into smaller fragments, releasing a large amount of energy. To maintain this process safely, it is necessary to control the rate of the chain reaction. This is where control rods play a vital role.

The material commonly used in control rods is cadmium. Cadmium has the ability to absorb excess neutrons without itself undergoing fission. Since neutrons are the particles that sustain the chain reaction, absorbing them slows down or even stops the reaction when required. By inserting or withdrawing the cadmium control rods from the reactor core, the fission process can be regulated with precision.

Here’s how the options compare:

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  Graphite is not used in control rods but instead acts as a moderator in some reactors. Its function is to slow down fast neutrons, making them more effective in sustaining the chain reaction.

  
  


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  Heavy water (D₂O) is also a moderator, not a control rod material. It slows down neutrons while allowing the chain reaction to continue efficiently.

  
  


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  Cadmium is the correct choice because it absorbs neutrons and directly controls the fission reaction. Other materials like boron and hafnium are also sometimes used in control rods for the same reason.

  
  

Thus, cadmium is crucial for reactor safety. Without control rods, the chain reaction could accelerate uncontrollably, leading to overheating and potentially dangerous situations.

In conclusion, the correct answer is Cadmium, as it is the primary material used in control rods to regulate nuclear fission in reactors.