Correct option is (a) Burner reactor
The explanation: Burner reactor is a type of reactor using U^235 as fuel. Enriched uranium is used to increase efficiency. To prolong the fission reaction, fast neutrons are slowed down with a moderator and the rate of reaction is adjusted by control rods which can absorb neutrons. Some neutrons react to form plutonium, but in smaller amounts than the original uranium, and produces only heat as a product.