What is the primary coolant used in CANDU reactors?

The primary coolant used in CANDU reactors is heavy water, also known as D2O. This choice is correct because heavy water has several beneficial properties that make it well-suited for use in nuclear reactors, particularly in the CANDU design.

CANDU reactors utilize heavy water as both a moderator and coolant, which allows them to use natural uranium as fuel. The effective neutron moderation provided by heavy water allows for a slower neutron spectrum that is more effective in sustaining the nuclear reactions with natural uranium. Additionally, heavy water has a higher boiling point and greater thermal capacity than light water, which contributes to more efficient heat transfer and improved safety margins in the event of operational anomalies.

The choice of heavy water also enables CANDU reactors to maintain a higher efficiency in their thermodynamic cycles, leading to better overall performance compared to reactors that use light water or other coolants. Furthermore, CANDU reactors can be designed to utilize various fuels, which broadens their adaptability in different operational contexts.

This unique use of heavy water distinguishes CANDU reactors from other reactor designs, which primarily rely on light water or other cooling methods.