Difficulty: Easy
Correct Answer: It produces more fissile fuel than it consumes during operation (net breeding).
Explanation:
Introduction / Context:
Breeder reactors are designed to increase the amount of fissile material by converting fertile isotopes (such as U-238 or Th-232) into fissile isotopes (Pu-239 or U-233). Understanding their defining feature and the typical design choices helps clarify common misconceptions.
Given Data / Assumptions:
Concept / Approach:
The hallmark of a breeder reactor is a breeding ratio greater than one: it generates more fissile material than it consumes. To favor breeding in U-238, fast neutrons are advantageous; therefore, fast breeder reactors avoid moderators and often employ coolants with low neutron moderation, such as liquid sodium or lead-bismuth eutectic. Fuel choices commonly include plutonium-based or mixed-oxide fuels rather than requiring highly enriched U-235 exclusively.
Step-by-Step Solution:
Identify defining feature: net production of fissile fuel → breeding ratio > 1.Design implication: avoid moderators to maintain a fast spectrum.Coolant choice: liquid sodium is common due to excellent heat transfer and low moderation.Fuel flexibility: can utilize plutonium or MOX with fertile blankets, not strictly highly enriched U-235.
Verification / Alternative check:
Historical fast breeder projects and literature describe sodium-cooled fast reactors with breeding blankets producing Pu-239 from U-238, exemplifying the principle.
Why Other Options Are Wrong:
Moderators are generally avoided in fast breeders (so (b) is false). Statement (c) is the opposite of practice since sodium is widely used as coolant. Statement (d) is incorrect because many breeders use plutonium or MOX fuels.
Common Pitfalls:
Confusing moderators with coolants and assuming all reactors require thermal moderation; breeder designs often deliberately maintain a fast spectrum.
Final Answer:
It produces more fissile fuel than it consumes during operation (net breeding).
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