This section provides introductory information about tritium and its properties.

Environmental Sources

Tritium occurs naturally in the environment. Reactions between cosmic rays and upper atmosphere constituents produce tritium. The following are examples of these reactions.

Tritium becomes incorporated into water and falls to earth as rain. At an estimated production rate of 4 x 10⁶ Ci/Yr, a world steady state natural inventory of 70 x 10⁶ Ci results.

Man-made Sources

Numerous potential and actual sources of tritium production exist in the United States, the United Kingdom, France, and other countries. They include light-water reactors, heavy-water reactors, fuel reprocessing facilities, and production reactors. Light-water reactors produce between 500 and 1000 Ci/yr of tritium in their coolant for every 1000 MW(e) of power. Heavy-water reactors produce approximately 2 x 10⁶ Ci/yr of tritium in their coolant for every 1,000 MW(e) of power.

Atomic Weight/Hydrogen Isotopes

The atomic weights, symbols, and abundance of the three well-known isotopes of hydrogen are given in Table 2. are also known. However, because they decay in fractions of a single second, they are not extensively studied. Unless otherwise specified in this chapter, the term hydrogen includes protium, deuterium, and tritium. will be used to refer to protium; confusion with elemental hydrogen will be eliminated by spelling out the latter.