Maybe I don't understand properly, but I'm watching the video linked in a previous comment (1) and around the minute 9:30 professor White says that "what comes into the plant is actually deuterium and lithium".
It seems he is saying that you need only an initial quantity of Tritium and then Helium and Lithium is used to created Tritium again. I suppose that it's what you refer as "breeding". He explain it as it's not a big deal.
