The moderating material most commonly selected for nuclear reactors is___________________?
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Answer: E. graphite
Explanation
Graphite is widely used as a high-purity moderator due to its excellent moderating ratio and low neutron capture cross-section. Carbon atoms in high-density graphite effectively slow down fast fission neutrons through elastic scattering collisions. Nuclear-grade graphite must be exceptionally pure to prevent boron and other trace impurities from absorbing vital neutrons. A neutron moderator slows down fast neutrons to thermal velocities, increasing the probability of fission with uranium-235. Ideal moderating materials possess low atomic mass numbers, high scattering cross-sections, and minimal neutron absorption. Graphite has historically served alongside heavy water and ordinary light water as a premier commercial reactor moderator.
Option A (heavy water) is an excellent moderator but is more expensive and used primarily in specialized reactor designs. Option B is incorrect because construction concrete and bricks contain absorbing impurities unsuited for effective moderation. Options C and E are partially correct but incomplete since graphite alone is the specific material referenced in standard contexts.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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