Kalpakkam FBTR (Fast Breeder Test Reactor): which statement correctly identifies a core design choice about fertile material/coolant/fuel form?

Introduction / Context:
Fast breeder reactors (FBRs) aim to produce more fissile material than they consume by converting a fertile isotope in a surrounding blanket into a fissile one. India’s Fast Breeder Test Reactor (FBTR) at Kalpakkam is a classic reference point for such questions.

Given Data / Assumptions:

• FBTR is a fast-spectrum reactor (no moderator).
• Typical fast breeders use a fertile blanket of U-238 that breeds fissile Pu-239.
• Coolant in many FBRs is liquid sodium (not helium or water).

Concept / Approach:
In a fast reactor, slowing down neutrons is undesirable; hence no moderator is used and liquid metals (often sodium) serve as the coolant due to excellent heat transfer properties at low pressure. The fertile blanket commonly comprises U-238 to breed Pu-239 via neutron capture. Thorium-232 based breeding is a different design line (e.g., advanced heavy-water or molten-salt thorium concepts) and does not describe the FBTR at Kalpakkam.

Step-by-Step Solution:
Recall that FBTR is a fast reactor without moderator.Identify the blanket: U-238 → Pu-239 breeding.Note coolant: liquid sodium in standard FBR practice (not helium or water).Exclude options that contradict these fundamentals; select U-238 as the fertile material.

Verification / Alternative check:
Standard FBR design summaries cite U-238 blankets and sodium coolant for the Kalpakkam FBTR lineage.

Why Other Options Are Wrong:
Thorium blanket: not characteristic of FBTR.Helium coolant: not the chosen coolant for FBTR.Uranium ore as fuel: fuel is fabricated fissile material, not raw ore.Water as moderator/coolant: contradicts fast-spectrum design.

Common Pitfalls:
Mixing up thorium-based R&D lines with India’s sodium-cooled breeder programme, or assuming all reactors use water as coolant.

Final Answer:
Uses U-238 as the fertile material in the blanket