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?

[amp_mcq option1=”1 and 3″ option2=”2 and 3″ option3=”4 only” option4=”1 and 4″ correct=”option2″]

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.

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