Heavy water
Hydrogen · Chemistry
Study notes
Why is D₂O used as a moderator in CANDU reactors? Step 1: Moderator must slow neutrons WITHOUT absorbing them. Step 2: D (deuterium) barely absorbs neutrons, unlike normal H which absorbs significantly. Step 3: D₂O slows neutrons efficiently through collisions (D is light). Step 4: Result: CANDU runs on natural (unenriched) uranium — D₂O's low absorption makes it possible!