Block 4 Nuclear Science Practice Exam

Which reactor type is commonly called CANDU and uses heavy water as both coolant and moderator?

Candu Reactor Light Water Reactors Magnox Reactor AGR Reactor

Correct Answer:

Candu Reactor

Explanation:

Heavy water as both coolant and moderator is the defining feature of the CANDU design. Deuterium oxide (heavy water) moderates neutrons very effectively while absorbing far fewer neutrons than ordinary water, so the reactor can run on natural uranium without enrichment. This setup also allows online refueling, which is a practical advantage of CANDU reactors. The other options use different cooling/moderation schemes—light water as the moderator and coolant, or gas-cooled with graphite moderator—so they do not employ heavy water in both roles.

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