Fusion reactors are considered an almost unlimited source of power for the future, with tritium [deuterium-tritium (D-T) mixture] being the most convenient fuel for these facilities. Due to tritium-specific features and its self-radioactivity there are a number of issues when handling a large amount of tritium for long-term operations of fusion reactors. This paper presents research results of tritium behavior in the D-T mixture and in the environment during operations at tritium facilities. The results provide the basis for an assessment of the future environmental effects of long-term operation of a fusion reactor/tritium facility. The results of experimental and modeling studies include tritium reactions with carbon oxides under radiolysis, radiolysis of DTO, tritium dispersion in atmosphere under rough terrain, tritium oxide washout from atmosphere, tritium oxidation in soil with soil bacteria, tritium oxide migration in the unsaturated soil layer, and tritium uptake by plants, crops, and lichens. Both experimental and observational data have been used to develop models to predict tritium behavior in the environment under similar conditions. The models have been verified and validated.