It is intended to use deuterium, an isotope of hydrogen, for commercial fusion when the time comes.
That and lithium. The only byproduct will be helium, of which one isotope that is expected to be produced in small quantities is slightly radioactive (half-life 12 years) and mildly poisonous in large quantities, but doesn't bio-accumulate the way things like mercury do.

Deuterium occurs in sea water at about 1 part per 6500, which doesn't sound like much but it means there is estimated to be enough in earth's oceans to meet our current energy consumption needs for the next 128 billion years. Yes, I said billion, not million.

That's why the EU spends 800 million euros a year on research into nuclear fusion, and rightly so.
(Vlad the Inhaler forgot his password, Wed 14 Jul 2010, 19:57, Reply)