Contamination mechanisms of air basin with tritium in venues of underground nuclear explosions at the former Semipalatinsk test site

► The basic mechanisms for tritium distribution in the air of nuclear testing sites were examined. ► We researched the distribution of tritium in the systems such as water-atmosphere, tunnel air-atmosphere, soil water-atmosphere and vegetation-atmosphere. ► An analytical calculation of tritium concentration in the atmosphere was performed. ► We experimentally obtained the dependence for predictive assessment of tritium concentrations in air as a function of tritium concentration in various sources.