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Q7 (CDS-II/2014) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Atomic and nuclear physics Answer Verified

Carbon or Graphite rods are used in atomic reactors as moderators for sustained nuclear chain reaction through nuclear fission process. In this process

Result
Your answer: —  Â·  Correct: C
Explanation

In a nuclear fission reactor, the process of moderation is essential for sustaining a chain reaction. When heavy isotopes like Uranium-235 undergo fission, they release high-energy 'fast' neutrons with kinetic energies typically around 2 MeV [3]. However, these fast neutrons are not easily absorbed by other fuel nuclei to trigger further fission. Carbon or graphite rods act as moderators by facilitating elastic collisions with these fast neutrons [1]. Through these collisions, the neutrons transfer their kinetic energy to the moderator atoms, effectively slowing them down until they reach 'thermal' energy levels [3]. These 'slow' or thermal neutrons have a much higher probability of being captured by the fuel atoms, thereby ensuring a continuous and controlled nuclear chain reaction [1]. Protons are not the target of this moderation process in atomic reactors.

Sources

  1. [1] https://www.sciencedirect.com/topics/immunology-and-microbiology/fission-neutron
  2. [3] https://www.osti.gov/servlets/purl/5603483
  3. [2] https://www.sciencedirect.com/topics/materials-science/moderator-material
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SIMILAR QUESTIONS

IAS · 2001 · Q106 Relevance score: 2.79

Consider the following statements : In a nuclear reactor, self-sustained chain reaction is possible, because I. more neutrons are released in each of the fission reactions. II. the neutrons immediately take part in the fission process. III. the fast neutrons are slowed down by Graphite. IV. every neutron realeased in the fission reaction initiates further fission. Which of these statements are correct ?

CAPF · 2010 · Q72 Relevance score: 1.18

Statement I : Heavy water is used as moderator in nuclear reactor. Statement I : Thermal neutrons are used for fission reaction in a reactor.

CDS-II · 2017 · Q60 Relevance score: 0.23

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?

NDA-I · 2009 · Q92 Relevance score: -0.17

Which one among the following is used as a moderator in nuclear reactors?