Consider the following statements: 1. The chain reaction process is

Consider the following statements:

  • 1. The chain reaction process is used in nuclear bombs to release a vast amount of energy, but in nuclear reactors, there is no chain reaction.
  • 2. In a nuclear reactor, the reaction is controlled, while in nuclear bombs, the reaction is uncontrolled.
  • 3. In a nuclear reactor, all operating reactors are ‘critical’, while there is no question of ‘criticality’ in case of a nuclear bomb.
  • 4. Nuclear reactors do not use moderators, while nuclear bombs use them.

Which of the above statements about operational principles of a nuclear reactor and a nuclear bomb is/are correct?

1 and 3
2 and 3
4 only
1 and 4
This question was previously asked in
UPSC CDS-2 – 2017
Statement 2 is correct: Nuclear reactors operate under controlled chain reactions, while nuclear bombs involve uncontrolled chain reactions. Statement 3 is also considered correct in this context, highlighting the difference in operation: reactors maintain a controlled ‘critical’ state, while bombs rapidly achieve an uncontrolled ‘supercritical’ state, distinct from sustained critical operation.
The fundamental difference is control: a reactor controls the neutron population to sustain a steady chain reaction, while a bomb allows the neutron population to grow exponentially and uncontrollably.
Statement 1 is incorrect; both use chain reactions. Statement 4 is incorrect; nuclear reactors *do* use moderators (like water, heavy water, or graphite) to slow down neutrons, which is necessary for fission in materials like U-235, whereas nuclear bombs typically use fast neutrons and do not use moderators. Statement 3 is slightly awkwardly phrased, as criticality is essential to both, but the *way* criticality is achieved and maintained (controlled vs. uncontrolled, sustained vs. rapid) is different. Given the options, Statement 3 is intended to represent this difference in operational state relative to criticality.