I first learned about tritium in chemistry classes at about the age of 15.
indeed, tritium has been used in watches to make parts of the dial glow in the dark, and a particularly expensive one is the Hublot Big Bang MP-11, which will lighten your wallet to the tune of a cool $96,000 in the US.
A rather more sinister use of tritium is in the manufacture of nuclear weapons, where it's used to increase fission efficiency in plutonium cores. A fission core that produces a yield of, say, 50 Kt without tritium in the hollow centre, can be boosted as far as 500 Kt when the hollow centre is fully filled with tritium.
You can take this process further, and use your boosted plutonium core as the primary in a thermonuclear weapon, then fill the cavity around the lithium deuteride secondary with more tritium, to increase the fusion yield of the secondary. Enclose the lot in a depleted uranium bomb case, and you have a "dial a yield" weapon that can be selected at launch to have a yield of anything between, say, 250 Kt and 25 megatons. Build a three-stage version and you could push the yield to a whopping 100 megatons and beyond - a weapon that size would be enough on its own to destroy the whole of, say, Latvia, with just one bomb.
You can take it as read that nuclear weapon designers have even more frightening designs on the books, if ever they feel the need to deploy them.
However, if nuclear fusion for power generation becomes an engineering reality, tritium will find heavy use in fusion reactors used for power generation. Out of all the possible fusion reactions, deuterium-tritium fusion is the simplest to initiate and sustain, once you've solved the containment and heat dissipation issues. It also produces a fair amount of liberated energy, to the point where a successful fusion reactor could be kept running using just 50 Kg of deuterium-tritium mix for 20 years or so. Keeping the requisite plasma tamed once it's heated to 100 million degrees is, as you can imagine, not easy, and solving that problem is currently exercising a lot of scientific minds.
