Naturally occurring tritium is extremely rare on Earth, where trace amounts are formed by the interaction of the atmosphere with cosmic rays.It can be produced by irradiating lithium metal or lithium-bearing ceramic pebbles in a nuclear reactor.
Since it continually decays into helium-3, the total amount remaining was about 75 kg (165 lb) at the time of the report.
Tritium for American nuclear weapons was produced in special heavy water reactors at the Savannah River Site until their closures in 1988.
Even so, cleaning tritium from the moderator may be desirable after several years to reduce the risk of its escaping to the environment.
Ontario Power Generation's "Tritium Removal Facility" processes up to 2,500 tonnes (2,500 long tons; 2,800 short tons) of heavy water a year, and it separates out about 2.5 kg (5.5 lb) of tritium, making it available for other uses.
The release or recovery of tritium needs to be considered in the operation of nuclear reactors, especially in the reprocessing of nuclear fuels and in the storage of spent nuclear fuel.
The production of tritium is not a goal, but rather a side-effect.
Radioluminescent 1.8 curies (67 GBq) 6 by 0.2 inches (152.4 mm × 5.1 mm) tritium vials are thin, tritium-gas-filled glass vials whose inner surfaces are coated with a phosphor. Like the other isotopes of hydrogen, tritium is difficult to confine.
Rubber, plastic, and some kinds of steel are all somewhat permeable.
The same is true, albeit to a lesser extent, of deuterium.