Heavy water is when deuterium and hydrogen get together and there is another neutron in hydrogen. It is naturally occurring. I don't remember what the percentage is, maybe 10% heavier than normal water. It's a natural kind of element. It's used to moderate, by which I mean to control, the nuclear reaction in a nuclear plant. That's the value of this heavy water. By itself, it's not radioactive. It is a naturally occurring thing. It's when a neutron is getting bombarded in this water that creates some of the radioactive elements.
Sorry, what was the second question you had?