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Question
Why deuterium instead of ordinary hydrogen?
Ordinary hydrogen fuses far too slowly for a power plant — it takes the sun billions of years. Deuterium fuses readily at temperatures a reactor can reach.
The choice of deuterium over ordinary hydrogen is really about reaction rate — see deuterium, fusion cross-section & reactivity, and the main fusion reactions.
Questions & answers
Why not just fuse ordinary hydrogen like the sun?
The sun fuses ordinary hydrogen (protons), but that reaction is astronomically slow — it relies on a rare quantum process and the sun's immense size and gravity, taking billions of years to burn its fuel. No power plant could use it. Deuterium, a heavier hydrogen isotope, fuses far more readily at temperatures we can actually reach.
What makes deuterium better for fusion?
Its reactions (with helium-3 or with itself) have much higher reaction rates at achievable temperatures. Deuterium is also abundant — extracted from seawater — so fuel supply is easy.
Is deuterium radioactive or dangerous?
No. Deuterium is a stable, non-radioactive isotope of hydrogen, present naturally in all water. It's completely safe to handle.