Tritium is produced in light-water-cooled reactors as a product of ternary fission and by nuclear reactions with the coolant and with neutron-absorbing materials used for reactor control. Pressurized water reactors (PWRs) have greater amounts of tritium produced in or released into the coolant than boiling water reactors (BWRs). Consequently, tritium releases to the environment from PWRs [29 GBq/MW(e)-y (0.78 Ci/MW(e)-y)] are about 6½ times greater than from BWRs [4.4 GBq/MW(e)-y (0.12 Ci/MW(e)-y)]. Most of the tritium released from PWRs appears in the liquid effluent (about 85%), whereas 75% of the tritium released from BWRs is as airborne effluents. Radiation doses from these tritium releases are small; the average site collective (population) dose in 1981 was less than 0.002 person-sieverts per year (0.2 person-rem/ year). The total collective dose from all tritium releases was 0.08 person-sieverts (8 person-rem).