3 1 H 3 2 He ¯ CHEMISTRY PARAMETERS DOE-HDBK-1015/2-93 Reactor Water Chemistry CH-03 Rev. 0 Page 24 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 10   Ci/yr of tritium 6 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.   H and  H are also known.  However, because they decay 4 5 1 1 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.    H 1 1 will be used to refer to protium; confusion with elemental hydrogen will be eliminated by spelling out the latter. TABLE 2 Hydrogen Isotopes Physical Common Name Abundance Mass Symbol Symbol (%) (amu) H H Protium 99.985 1.007825 1 1 H D Deuterium 0.015 2.01400 2 1 H T Tritium emitter* 3.01605 3 1 - * 12.32-years half-life Disintegration Tritium  decays  by  emitting  a  weak  beta  particle  together  with  an  antineutrino.    The product is helium-3.  Helium is a monatomic gas; therefore, the decay of 1 mole of T₂ yields 2 moles of helium.  This causes a pressure buildup in sealed vessels containing diatomic tritium gas (or HT or DT gas).  The following reaction is tritium disintegration.