Understanding Steam Generating Heavy Water Reactors (SGHWR)

The question asks to identify a specific type of nuclear reactor based on its key components: the fuel used, the moderator, and the coolant.

Let's break down the characteristics provided:

• Fuel: UO₂ pellets enriched to 2.3%. This indicates low enrichment, typical for thermal reactors that use a moderator. Fast breeder reactors, for instance, use much higher enrichment or plutonium fuel and do not require a moderator.
• Moderator: D₂O (Heavy Water). A moderator is used to slow down fast neutrons produced by fission to thermal energies, making them more likely to cause further fission in the fuel. Heavy water is an excellent moderator.
• Coolant: Water. The coolant removes the heat generated by nuclear fission. In some reactor designs, the coolant also acts as the moderator.

Now let's examine the given options in light of these characteristics:

• Fast breeder reactor: These reactors do not use a moderator (they use fast neutrons). They also typically use highly enriched fuel or plutonium. This does not match the description of using D₂O as a moderator.
• Boiling water reactor (BWR): These reactors use light water (H₂O) as both the moderator and the coolant. The description specifies D₂O as the moderator, so this option is incorrect.
• Pressurised water reactor (PWR): Similar to BWRs, PWRs use light water (H₂O) as both the moderator and the coolant. The description specifies D₂O as the moderator, making this option incorrect.
• Steam generating heavy water reactor: This type of reactor specifically uses heavy water (D₂O) as the moderator but uses light water (H₂O) as the coolant. The coolant boils within the fuel channels to produce steam directly, which then drives turbines. This configuration perfectly matches the description: UO₂ fuel, D₂O moderator, and water coolant (light water in this case, used for steam generation).

Based on the analysis, the reactor type that uses UO₂ fuel enriched to 2.3%, D₂O as moderators, and water as coolant is the Steam Generating Heavy Water Reactor.