Tritium is a heavy isotope of hydrogen having 1 each proton and electron, and 2 neutrons.
You asked, given that it has a half-life of 12.3 years, where does it come from?
Do we recycle it?
What about the future?
I particularly enjoyed researching these questions. The primary natural source is cosmic radiation striking nitrogen high in our atmosphere. In the same reaction that creates carbon-14, allowing us to use radiocarbon dating of formerly living tissue, tritium is the other product. (I am amazed.) This production is slow enough and the half-life is short enough that there is only a trace of natural tritium in the atmosphere. (Carbon-14 amounts to about one trillionth of all the carbon on Earth and is much more stable than tritium.)
Tritium can be produced in nuclear reactors by exposing isotopes of lithium and boron to neutrons. The actual reactions are described in Internet articles, but I won't pretend I can explain them.
A physicist friend of mine tells me that for the most part, the U.S. is not making new tritium, but rather recycling it from the stock left by decommissioning weapons. This supply is slipping away as we use it and as its half-life dictates. Jim said that there are several ideas for eventually replenishing our supply using particle accelerators or nuclear reactors.
My personal favorite tritium factoid: Willard F. Libby, one of my all-time heroes, the developer of radiocarbon dating, used tritium for dating the water in wine. I suppose most wine is too young for carbon-14 (Half life ~5730 years) dating. (The United States requires that wine be slightly radioactive, but that is a different discussion.)
